Merge branch 'master' into Pale_Moon-release

# Conflicts:
#	application/palemoon/config/version.txt
#	security/manager/ssl/nsSTSPreloadList.errors
#	security/manager/ssl/nsSTSPreloadList.inc

107 files changed, 1162 insertions, 8609 deletions

diff --git a/js/src/builtin/Array.js b/js/src/builtin/Array.js
index 30e6fb35f..05fc41bc1 100644
--- a/js/src/builtin/Array.js
+++ b/js/src/builtin/Array.js
@@ -1073,6 +1073,114 @@ function ArrayConcat(arg1) {
     return A;
 }
 
+// https://tc39.github.io/proposal-flatMap/
+// January 4, 2019
+function ArrayFlatMap(mapperFunction/*, thisArg*/) {
+    // Step 1.
+    var O = ToObject(this);
+
+    // Step 2.
+    var sourceLen = ToLength(O.length);
+
+    // Step 3.
+    if (!IsCallable(mapperFunction))
+        ThrowTypeError(JSMSG_NOT_FUNCTION, DecompileArg(0, mapperFunction));
+
+    // Step 4.
+    var T = arguments.length > 1 ? arguments[1] : undefined;
+
+    // Step 5.
+    var A = ArraySpeciesCreate(O, 0);
+
+    // Step 6.
+    FlattenIntoArray(A, O, sourceLen, 0, 1, mapperFunction, T);
+
+    // Step 7.
+    return A;
+}
+
+// https://tc39.github.io/proposal-flatMap/
+// January 4, 2019
+function ArrayFlat(/* depth */) {
+     // Step 1.
+    var O = ToObject(this);
+
+    // Step 2.
+    var sourceLen = ToLength(O.length);
+
+    // Step 3.
+    var depthNum = 1;
+
+    // Step 4.
+    if (arguments.length > 0 && arguments[0] !== undefined)
+        depthNum = ToInteger(arguments[0]);
+
+    // Step 5.
+    var A = ArraySpeciesCreate(O, 0);
+
+    // Step 6.
+    FlattenIntoArray(A, O, sourceLen, 0, depthNum);
+
+    // Step 7.
+    return A;
+}
+
+// https://tc39.github.io/proposal-flatMap/
+// January 4, 2019
+function FlattenIntoArray(target, source, sourceLen, start, depth, mapperFunction, thisArg) {
+    // Step 1.
+    var targetIndex = start;
+
+    // Steps 2-3.
+    for (var sourceIndex = 0; sourceIndex < sourceLen; sourceIndex++) {
+        // Steps 3.a-c.
+        if (sourceIndex in source) {
+            // Step 3.c.i.
+            var element = source[sourceIndex];
+
+            if (mapperFunction) {
+                // Step 3.c.ii.1.
+                assert(arguments.length === 7, "thisArg is present");
+
+                // Step 3.c.ii.2.
+                element = callContentFunction(mapperFunction, thisArg, element, sourceIndex, source);
+            }
+
+            // Step 3.c.iii.
+            var shouldFlatten = false;
+
+            // Step 3.c.iv.
+            if (depth > 0) {
+                // Step 3.c.iv.1.
+                shouldFlatten = IsArray(element);
+            }
+
+            // Step 3.c.v.
+            if (shouldFlatten) {
+                // Step 3.c.v.1.
+                var elementLen = ToLength(element.length);
+
+                // Step 3.c.v.2.
+                // Recursive call to walk the depth.
+                targetIndex = FlattenIntoArray(target, element, elementLen, targetIndex, depth - 1);
+            } else {
+                // Step 3.c.vi.1.
+                if (targetIndex >= MAX_NUMERIC_INDEX)
+                    ThrowTypeError(JSMSG_TOO_LONG_ARRAY);
+
+                // Step 3.c.vi.2.
+                _DefineDataProperty(target, targetIndex, element);
+
+                // Step 3.c.vi.3.
+                targetIndex++;
+            }
+        }
+    }
+
+    // Step 4.
+    return targetIndex;
+}
+
 function ArrayStaticConcat(arr, arg1) {
     if (arguments.length < 1)
         ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'Array.concat');
diff --git a/js/src/builtin/AtomicsObject.cpp b/js/src/builtin/AtomicsObject.cpp
index 2551f3b7d..3de3f5f4c 100644
--- a/js/src/builtin/AtomicsObject.cpp
+++ b/js/src/builtin/AtomicsObject.cpp
@@ -834,7 +834,7 @@ js::atomics_wait(JSContext* cx, unsigned argc, Value* vp)
 }
 
 bool
-js::atomics_wake(JSContext* cx, unsigned argc, Value* vp)
+js::atomics_notify(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
     HandleValue objv = args.get(0);
@@ -874,7 +874,7 @@ js::atomics_wake(JSContext* cx, unsigned argc, Value* vp)
             iter = iter->lower_pri;
             if (c->offset != offset || !c->rt->fx.isWaiting())
                 continue;
-            c->rt->fx.wake(FutexRuntime::WakeExplicit);
+            c->rt->fx.notify(FutexRuntime::NotifyExplicit);
             ++woken;
             --count;
         } while (count > 0 && iter != waiters);
@@ -950,7 +950,7 @@ js::FutexRuntime::isWaiting()
     // When a worker is awoken for an interrupt it goes into state
     // WaitingNotifiedForInterrupt for a short time before it actually
     // wakes up and goes into WaitingInterrupted.  In those states the
-    // worker is still waiting, and if an explicit wake arrives the
+    // worker is still waiting, and if an explicit notify arrives the
     // worker transitions to Woken.  See further comments in
     // FutexRuntime::wait().
     return state_ == Waiting || state_ == WaitingInterrupted || state_ == WaitingNotifiedForInterrupt;
@@ -1029,14 +1029,14 @@ js::FutexRuntime::wait(JSContext* cx, js::UniqueLock<js::Mutex>& locked,
             //   should be woken when the interrupt handler returns.
             //   To that end, we flag the thread as interrupted around
             //   the interrupt and check state_ when the interrupt
-            //   handler returns.  A wake() call that reaches the
+            //   handler returns.  A notify() call that reaches the
             //   runtime during the interrupt sets state_ to Woken.
             //
             // - It is in principle possible for wait() to be
             //   reentered on the same thread/runtime and waiting on the
             //   same location and to yet again be interrupted and enter
             //   the interrupt handler.  In this case, it is important
-            //   that when another agent wakes waiters, all waiters using
+            //   that when another agent notifies waiters, all waiters using
             //   the same runtime on the same location are woken in LIFO
             //   order; FIFO may be the required order, but FIFO would
             //   fail to wake up the innermost call.  Interrupts are
@@ -1073,25 +1073,25 @@ finished:
 }
 
 void
-js::FutexRuntime::wake(WakeReason reason)
+js::FutexRuntime::notify(NotifyReason reason)
 {
     MOZ_ASSERT(isWaiting());
 
-    if ((state_ == WaitingInterrupted || state_ == WaitingNotifiedForInterrupt) && reason == WakeExplicit) {
+    if ((state_ == WaitingInterrupted || state_ == WaitingNotifiedForInterrupt) && reason == NotifyExplicit) {
         state_ = Woken;
         return;
     }
     switch (reason) {
-      case WakeExplicit:
+      case NotifyExplicit:
         state_ = Woken;
         break;
-      case WakeForJSInterrupt:
+      case NotifyForJSInterrupt:
         if (state_ == WaitingNotifiedForInterrupt)
             return;
         state_ = WaitingNotifiedForInterrupt;
         break;
       default:
-        MOZ_CRASH("bad WakeReason in FutexRuntime::wake()");
+        MOZ_CRASH("bad NotifyReason in FutexRuntime::notify()");
     }
     cond_->notify_all();
 }
@@ -1108,7 +1108,8 @@ const JSFunctionSpec AtomicsMethods[] = {
     JS_INLINABLE_FN("xor",                atomics_xor,                3,0, AtomicsXor),
     JS_INLINABLE_FN("isLockFree",         atomics_isLockFree,         1,0, AtomicsIsLockFree),
     JS_FN("wait",                         atomics_wait,               4,0),
-    JS_FN("wake",                         atomics_wake,               3,0),
+    JS_FN("notify",                       atomics_notify,             3,0),
+    JS_FN("wake",                         atomics_notify,             3,0), //Legacy name
     JS_FS_END
 };
 
diff --git a/js/src/builtin/AtomicsObject.h b/js/src/builtin/AtomicsObject.h
index adb6fb986..6511dc8bf 100644
--- a/js/src/builtin/AtomicsObject.h
+++ b/js/src/builtin/AtomicsObject.h
@@ -36,7 +36,7 @@ MOZ_MUST_USE bool atomics_or(JSContext* cx, unsigned argc, Value* vp);
 MOZ_MUST_USE bool atomics_xor(JSContext* cx, unsigned argc, Value* vp);
 MOZ_MUST_USE bool atomics_isLockFree(JSContext* cx, unsigned argc, Value* vp);
 MOZ_MUST_USE bool atomics_wait(JSContext* cx, unsigned argc, Value* vp);
-MOZ_MUST_USE bool atomics_wake(JSContext* cx, unsigned argc, Value* vp);
+MOZ_MUST_USE bool atomics_notify(JSContext* cx, unsigned argc, Value* vp);
 
 /* asm.js callouts */
 namespace wasm { class Instance; }
@@ -63,10 +63,10 @@ public:
     MOZ_MUST_USE bool initInstance();
     void destroyInstance();
 
-    // Parameters to wake().
-    enum WakeReason {
-        WakeExplicit,           // Being asked to wake up by another thread
-        WakeForJSInterrupt      // Interrupt requested
+    // Parameters to notify().
+    enum NotifyReason {
+        NotifyExplicit,           // Being asked to wake up by another thread
+        NotifyForJSInterrupt      // Interrupt requested
     };
 
     // Result code from wait().
@@ -83,29 +83,27 @@ public:
     // times allowed; specify mozilla::Nothing() for an indefinite
     // wait.
     //
-    // wait() will not wake up spuriously.  It will return true and
-    // set *result to a return code appropriate for
-    // Atomics.wait() on success, and return false on error.
+    // wait() will not wake up spuriously.
     MOZ_MUST_USE bool wait(JSContext* cx, js::UniqueLock<js::Mutex>& locked,
                            mozilla::Maybe<mozilla::TimeDuration>& timeout, WaitResult* result);
 
-    // Wake the thread represented by this Runtime.
+    // Notify the thread represented by this Runtime.
     //
     // The futex lock must be held around this call.  (The sleeping
-    // thread will not wake up until the caller of Atomics.wake()
+    // thread will not wake up until the caller of Atomics.notify()
     // releases the lock.)
     //
     // If the thread is not waiting then this method does nothing.
     //
     // If the thread is waiting in a call to wait() and the
-    // reason is WakeExplicit then the wait() call will return
+    // reason is NotifyExplicit then the wait() call will return
     // with Woken.
     //
     // If the thread is waiting in a call to wait() and the
-    // reason is WakeForJSInterrupt then the wait() will return
+    // reason is NotifyForJSInterrupt then the wait() will return
     // with WaitingNotifiedForInterrupt; in the latter case the caller
     // of wait() must handle the interrupt.
-    void wake(WakeReason reason);
+    void notify(NotifyReason reason);
 
     bool isWaiting();
 
@@ -128,7 +126,7 @@ public:
                                      //   interrupt handler
         WaitingInterrupted,          // We are waiting, but have been interrupted
                                      //   and are running the interrupt handler
-        Woken                        // Woken by a script call to Atomics.wake
+        Woken                        // Woken by a script call to Atomics.notify
     };
 
     // Condition variable that this runtime will wait on.
diff --git a/js/src/builtin/IntlTimeZoneData.h b/js/src/builtin/IntlTimeZoneData.h
index fa808c0b9..8f963ffbc 100644
--- a/js/src/builtin/IntlTimeZoneData.h
+++ b/js/src/builtin/IntlTimeZoneData.h
@@ -1,5 +1,5 @@
 // Generated by make_intl_data.py. DO NOT EDIT.
-// tzdata version = 2018e
+// tzdata version = 2019a
 
 #ifndef builtin_IntlTimeZoneData_h
 #define builtin_IntlTimeZoneData_h
diff --git a/js/src/builtin/ModuleObject.cpp b/js/src/builtin/ModuleObject.cpp
index 710c7a76c..c6bd2d300 100644
--- a/js/src/builtin/ModuleObject.cpp
+++ b/js/src/builtin/ModuleObject.cpp
@@ -947,7 +947,7 @@ ModuleObject::evaluate(JSContext* cx, HandleModuleObject self, MutableHandleValu
 ModuleObject::createNamespace(JSContext* cx, HandleModuleObject self, HandleObject exports)
 {
     MOZ_ASSERT(!self->namespace_());
-    MOZ_ASSERT(exports->is<ArrayObject>() || exports->is<UnboxedArrayObject>());
+    MOZ_ASSERT(exports->is<ArrayObject>());
 
     RootedModuleNamespaceObject ns(cx, ModuleNamespaceObject::create(cx, self));
     if (!ns)
diff --git a/js/src/builtin/String.js b/js/src/builtin/String.js
index e5b2ad552..f830b1aa2 100644
--- a/js/src/builtin/String.js
+++ b/js/src/builtin/String.js
@@ -828,16 +828,16 @@ function String_static_trim(string) {
     return callFunction(std_String_trim, string);
 }
 
-function String_static_trimLeft(string) {
+function String_static_trimStart(string) {
     if (arguments.length < 1)
-        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'String.trimLeft');
-    return callFunction(std_String_trimLeft, string);
+        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'String.trimStart');
+    return callFunction(std_String_trimStart, string);
 }
 
-function String_static_trimRight(string) {
+function String_static_trimEnd(string) {
     if (arguments.length < 1)
-        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'String.trimRight');
-    return callFunction(std_String_trimRight, string);
+        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'String.trimEnd');
+    return callFunction(std_String_trimEnd, string);
 }
 
 function String_static_toLocaleLowerCase(string) {
diff --git a/js/src/builtin/SymbolObject.cpp b/js/src/builtin/SymbolObject.cpp
index cf48402d6..ae38d5371 100644
--- a/js/src/builtin/SymbolObject.cpp
+++ b/js/src/builtin/SymbolObject.cpp
@@ -33,6 +33,7 @@ SymbolObject::create(JSContext* cx, JS::HandleSymbol symbol)
 }
 
 const JSPropertySpec SymbolObject::properties[] = {
+    JS_PSG("description", descriptionGetter, 0),
     JS_PS_END
 };
 
@@ -227,6 +228,34 @@ SymbolObject::toPrimitive(JSContext* cx, unsigned argc, Value* vp)
     return CallNonGenericMethod<IsSymbol, valueOf_impl>(cx, args);
 }
 
+// ES2019 Stage 4 Draft / November 28, 2018
+// Symbol description accessor
+// See: https://tc39.github.io/proposal-Symbol-description/
+bool
+SymbolObject::descriptionGetter_impl(JSContext* cx, const CallArgs& args)
+{
+    // Get symbol object pointer.
+    HandleValue thisv = args.thisv();
+    MOZ_ASSERT(IsSymbol(thisv));
+    Rooted<Symbol*> sym(cx, thisv.isSymbol()
+                            ? thisv.toSymbol()
+                            : thisv.toObject().as<SymbolObject>().unbox());
+
+    // Return the symbol's description if present, otherwise return undefined.
+    if (JSString* str = sym->description())
+        args.rval().setString(str);
+    else
+        args.rval().setUndefined();
+    return true;
+}
+
+bool
+SymbolObject::descriptionGetter(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return CallNonGenericMethod<IsSymbol, descriptionGetter_impl>(cx, args);
+}
+
 JSObject*
 js::InitSymbolClass(JSContext* cx, HandleObject obj)
 {
diff --git a/js/src/builtin/SymbolObject.h b/js/src/builtin/SymbolObject.h
index 0f204b494..e10b42d53 100644
--- a/js/src/builtin/SymbolObject.h
+++ b/js/src/builtin/SymbolObject.h
@@ -52,6 +52,10 @@ class SymbolObject : public NativeObject
     static MOZ_MUST_USE bool valueOf(JSContext* cx, unsigned argc, Value* vp);
     static MOZ_MUST_USE bool toPrimitive(JSContext* cx, unsigned argc, Value* vp);
 
+    // Properties defined on Symbol.prototype.
+    static MOZ_MUST_USE bool descriptionGetter_impl(JSContext* cx, const CallArgs& args);
+    static MOZ_MUST_USE bool descriptionGetter(JSContext* cx, unsigned argc, Value *vp);
+
     static const JSPropertySpec properties[];
     static const JSFunctionSpec methods[];
     static const JSFunctionSpec staticMethods[];
diff --git a/js/src/builtin/TypedObject.cpp b/js/src/builtin/TypedObject.cpp
index ae74f01bf..0dfc1123a 100644
--- a/js/src/builtin/TypedObject.cpp
+++ b/js/src/builtin/TypedObject.cpp
@@ -652,7 +652,7 @@ ArrayMetaTypeDescr::create(JSContext* cx,
     if (!CreateTraceList(cx, obj))
         return nullptr;
 
-    if (!cx->zone()->typeDescrObjects.put(obj)) {
+    if (!cx->zone()->addTypeDescrObject(cx, obj)) {
         ReportOutOfMemory(cx);
         return nullptr;
     }
@@ -993,8 +993,8 @@ StructMetaTypeDescr::create(JSContext* cx,
     if (!CreateTraceList(cx, descr))
         return nullptr;
 
-    if (!cx->zone()->typeDescrObjects.put(descr) ||
-        !cx->zone()->typeDescrObjects.put(fieldTypeVec))
+    if (!cx->zone()->addTypeDescrObject(cx, descr) ||
+        !cx->zone()->addTypeDescrObject(cx, fieldTypeVec))
     {
         ReportOutOfMemory(cx);
         return nullptr;
@@ -1165,10 +1165,8 @@ DefineSimpleTypeDescr(JSContext* cx,
     if (!CreateTraceList(cx, descr))
         return false;
 
-    if (!cx->zone()->typeDescrObjects.put(descr)) {
-        ReportOutOfMemory(cx);
+    if (!cx->zone()->addTypeDescrObject(cx, descr))
         return false;
-    }
 
     return true;
 }
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index c524184d6..7f9fa8a5d 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -6281,8 +6281,8 @@ ParseNode::getConstantValue(ExclusiveContext* cx, AllowConstantObjects allowObje
         }
         MOZ_ASSERT(idx == count);
 
-        JSObject* obj = ObjectGroup::newArrayObject(cx, values.begin(), values.length(),
-                                                    newKind, arrayKind);
+        ArrayObject* obj = ObjectGroup::newArrayObject(cx, values.begin(), values.length(),
+                                                       newKind, arrayKind);
         if (!obj)
             return false;
 
@@ -9192,7 +9192,7 @@ BytecodeEmitter::emitCallOrNew(ParseNode* pn)
                 return false;
         }
 
-        if (!emitArray(args, argc, JSOP_SPREADCALLARRAY))
+        if (!emitArray(args, argc))
             return false;
 
         if (optCodeEmitted) {
@@ -9683,11 +9683,11 @@ BytecodeEmitter::emitArrayLiteral(ParseNode* pn)
         }
     }
 
-    return emitArray(pn->pn_head, pn->pn_count, JSOP_NEWARRAY);
+    return emitArray(pn->pn_head, pn->pn_count);
 }
 
 bool
-BytecodeEmitter::emitArray(ParseNode* pn, uint32_t count, JSOp op)
+BytecodeEmitter::emitArray(ParseNode* pn, uint32_t count)
 {
 
     /*
@@ -9698,7 +9698,6 @@ BytecodeEmitter::emitArray(ParseNode* pn, uint32_t count, JSOp op)
      * to avoid dup'ing and popping the array as each element is added, as
      * JSOP_SETELEM/JSOP_SETPROP would do.
      */
-    MOZ_ASSERT(op == JSOP_NEWARRAY || op == JSOP_SPREADCALLARRAY);
 
     uint32_t nspread = 0;
     for (ParseNode* elt = pn; elt; elt = elt->pn_next) {
@@ -9719,7 +9718,7 @@ BytecodeEmitter::emitArray(ParseNode* pn, uint32_t count, JSOp op)
 
     // For arrays with spread, this is a very pessimistic allocation, the
     // minimum possible final size.
-    if (!emitUint32Operand(op, count - nspread))                    // ARRAY
+    if (!emitUint32Operand(JSOP_NEWARRAY, count - nspread))         // ARRAY
         return false;
 
     ParseNode* pn2 = pn;
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 814fa11d4..29050c846 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -521,7 +521,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     MOZ_MUST_USE bool emitAtomOp(ParseNode* pn, JSOp op);
 
     MOZ_MUST_USE bool emitArrayLiteral(ParseNode* pn);
-    MOZ_MUST_USE bool emitArray(ParseNode* pn, uint32_t count, JSOp op);
+    MOZ_MUST_USE bool emitArray(ParseNode* pn, uint32_t count);
     MOZ_MUST_USE bool emitArrayComp(ParseNode* pn);
 
     MOZ_MUST_USE bool emitInternedScopeOp(uint32_t index, JSOp op);
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index daacbb50b..3b7a0e612 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -2310,7 +2310,6 @@ Parser<FullParseHandler>::standaloneFunction(HandleFunction fun,
     if (!tokenStream.getToken(&tt))
         return null();
     if (asyncKind == AsyncFunction) {
-        MOZ_ASSERT(tt == TOK_ASYNC);
         if (!tokenStream.getToken(&tt))
             return null();
     }
diff --git a/js/src/gc/GCRuntime.h b/js/src/gc/GCRuntime.h
index 5c2576efd..f102e9ef0 100644
--- a/js/src/gc/GCRuntime.h
+++ b/js/src/gc/GCRuntime.h
@@ -900,7 +900,8 @@ class GCRuntime
 
     void requestMajorGC(JS::gcreason::Reason reason);
     SliceBudget defaultBudget(JS::gcreason::Reason reason, int64_t millis);
-    void budgetIncrementalGC(SliceBudget& budget, AutoLockForExclusiveAccess& lock);
+    void budgetIncrementalGC(JS::gcreason::Reason reason, SliceBudget& budget,
+                             AutoLockForExclusiveAccess& lock);
     void resetIncrementalGC(AbortReason reason, AutoLockForExclusiveAccess& lock);
 
     // Assert if the system state is such that we should never
@@ -915,6 +916,7 @@ class GCRuntime
     void collect(bool nonincrementalByAPI, SliceBudget budget, JS::gcreason::Reason reason) JS_HAZ_GC_CALL;
     MOZ_MUST_USE bool gcCycle(bool nonincrementalByAPI, SliceBudget& budget,
                               JS::gcreason::Reason reason);
+    bool shouldRepeatForDeadZone(JS::gcreason::Reason reason);
     void incrementalCollectSlice(SliceBudget& budget, JS::gcreason::Reason reason,
                                  AutoLockForExclusiveAccess& lock);
 
diff --git a/js/src/gc/Marking.cpp b/js/src/gc/Marking.cpp
index 3ea4c9d29..da3ef7d0d 100644
--- a/js/src/gc/Marking.cpp
+++ b/js/src/gc/Marking.cpp
@@ -18,6 +18,7 @@
 #include "builtin/ModuleObject.h"
 #include "gc/GCInternals.h"
 #include "gc/Policy.h"
+#include "gc/StoreBuffer-inl.h"
 #include "jit/IonCode.h"
 #include "js/SliceBudget.h"
 #include "vm/ArgumentsObject.h"
@@ -28,7 +29,6 @@
 #include "vm/Shape.h"
 #include "vm/Symbol.h"
 #include "vm/TypedArrayObject.h"
-#include "vm/UnboxedObject.h"
 #include "wasm/WasmJS.h"
 
 #include "jscompartmentinlines.h"
@@ -37,7 +37,6 @@
 
 #include "gc/Nursery-inl.h"
 #include "vm/String-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using namespace js;
 using namespace js::gc;
@@ -1395,14 +1394,6 @@ js::ObjectGroup::traceChildren(JSTracer* trc)
     if (maybePreliminaryObjects())
         maybePreliminaryObjects()->trace(trc);
 
-    if (maybeUnboxedLayout())
-        unboxedLayout().trace(trc);
-
-    if (ObjectGroup* unboxedGroup = maybeOriginalUnboxedGroup()) {
-        TraceManuallyBarrieredEdge(trc, &unboxedGroup, "group_original_unboxed_group");
-        setOriginalUnboxedGroup(unboxedGroup);
-    }
-
     if (JSObject* descr = maybeTypeDescr()) {
         TraceManuallyBarrieredEdge(trc, &descr, "group_type_descr");
         setTypeDescr(&descr->as<TypeDescr>());
@@ -1436,12 +1427,6 @@ js::GCMarker::lazilyMarkChildren(ObjectGroup* group)
     if (group->maybePreliminaryObjects())
         group->maybePreliminaryObjects()->trace(this);
 
-    if (group->maybeUnboxedLayout())
-        group->unboxedLayout().trace(this);
-
-    if (ObjectGroup* unboxedGroup = group->maybeOriginalUnboxedGroup())
-        traverseEdge(group, unboxedGroup);
-
     if (TypeDescr* descr = group->maybeTypeDescr())
         traverseEdge(group, static_cast<JSObject*>(descr));
 
@@ -1484,23 +1469,6 @@ CallTraceHook(Functor f, JSTracer* trc, JSObject* obj, CheckGeneration check, Ar
         return nullptr;
     }
 
-    if (clasp == &UnboxedPlainObject::class_) {
-        JSObject** pexpando = obj->as<UnboxedPlainObject>().addressOfExpando();
-        if (*pexpando)
-            f(pexpando, mozilla::Forward<Args>(args)...);
-
-        UnboxedPlainObject& unboxed = obj->as<UnboxedPlainObject>();
-        const UnboxedLayout& layout = check == CheckGeneration::DoChecks
-                                      ? unboxed.layout()
-                                      : unboxed.layoutDontCheckGeneration();
-        if (layout.traceList()) {
-            VisitTraceList(f, layout.traceList(), unboxed.data(),
-                           mozilla::Forward<Args>(args)...);
-        }
-
-        return nullptr;
-    }
-
     clasp->doTrace(trc, obj);
 
     if (!clasp->isNative())
@@ -2293,18 +2261,6 @@ static inline void
 TraceWholeCell(TenuringTracer& mover, JSObject* object)
 {
     mover.traceObject(object);
-
-    // Additionally trace the expando object attached to any unboxed plain
-    // objects. Baseline and Ion can write properties to the expando while
-    // only adding a post barrier to the owning unboxed object. Note that
-    // it isn't possible for a nursery unboxed object to have a tenured
-    // expando, so that adding a post barrier on the original object will
-    // capture any tenured->nursery edges in the expando as well.
-
-    if (object->is<UnboxedPlainObject>()) {
-        if (UnboxedExpandoObject* expando = object->as<UnboxedPlainObject>().maybeExpando())
-            expando->traceChildren(&mover);
-    }
 }
 
 static inline void
@@ -2548,8 +2504,6 @@ js::TenuringTracer::moveObjectToTenured(JSObject* dst, JSObject* src, AllocKind
         InlineTypedObject::objectMovedDuringMinorGC(this, dst, src);
     } else if (src->is<TypedArrayObject>()) {
         tenuredSize += TypedArrayObject::objectMovedDuringMinorGC(this, dst, src, dstKind);
-    } else if (src->is<UnboxedArrayObject>()) {
-        tenuredSize += UnboxedArrayObject::objectMovedDuringMinorGC(this, dst, src, dstKind);
     } else if (src->is<ArgumentsObject>()) {
         tenuredSize += ArgumentsObject::objectMovedDuringMinorGC(this, dst, src);
     } else if (src->is<ProxyObject>()) {
diff --git a/js/src/gc/RootMarking.cpp b/js/src/gc/RootMarking.cpp
index 93264084b..f5969bc1f 100644
--- a/js/src/gc/RootMarking.cpp
+++ b/js/src/gc/RootMarking.cpp
@@ -478,6 +478,7 @@ js::gc::GCRuntime::bufferGrayRoots()
     for (GCZonesIter zone(rt); !zone.done(); zone.next())
         MOZ_ASSERT(zone->gcGrayRoots.empty());
 
+    gcstats::AutoPhase ap(stats, gcstats::PHASE_BUFFER_GRAY_ROOTS);
 
     BufferGrayRootsTracer grayBufferer(rt);
     if (JSTraceDataOp op = grayRootTracer.op)
@@ -540,4 +541,3 @@ GCRuntime::resetBufferedGrayRoots() const
     for (GCZonesIter zone(rt); !zone.done(); zone.next())
         zone->gcGrayRoots.clearAndFree();
 }
-
diff --git a/js/src/gc/Tracer.cpp b/js/src/gc/Tracer.cpp
index 63cd9b08a..3416464dd 100644
--- a/js/src/gc/Tracer.cpp
+++ b/js/src/gc/Tracer.cpp
@@ -201,80 +201,15 @@ gc::TraceCycleCollectorChildren(JS::CallbackTracer* trc, Shape* shape)
     } while (shape);
 }
 
-// Object groups can point to other object groups via an UnboxedLayout or the
-// the original unboxed group link. There can potentially be deep or cyclic
-// chains of such groups to trace through without going through a thing that
-// participates in cycle collection. These need to be handled iteratively to
-// avoid blowing the stack when running the cycle collector's callback tracer.
-struct ObjectGroupCycleCollectorTracer : public JS::CallbackTracer
-{
-    explicit ObjectGroupCycleCollectorTracer(JS::CallbackTracer* innerTracer)
-        : JS::CallbackTracer(innerTracer->runtime(), DoNotTraceWeakMaps),
-          innerTracer(innerTracer)
-    {}
-
-    void onChild(const JS::GCCellPtr& thing) override;
-
-    JS::CallbackTracer* innerTracer;
-    Vector<ObjectGroup*, 4, SystemAllocPolicy> seen, worklist;
-};
-
-void
-ObjectGroupCycleCollectorTracer::onChild(const JS::GCCellPtr& thing)
-{
-    if (thing.is<BaseShape>()) {
-        // The CC does not care about BaseShapes, and no additional GC things
-        // will be reached by following this edge.
-        return;
-    }
-
-    if (thing.is<JSObject>() || thing.is<JSScript>()) {
-        // Invoke the inner cycle collector callback on this child. It will not
-        // recurse back into TraceChildren.
-        innerTracer->onChild(thing);
-        return;
-    }
-
-    if (thing.is<ObjectGroup>()) {
-        // If this group is required to be in an ObjectGroup chain, trace it
-        // via the provided worklist rather than continuing to recurse.
-        ObjectGroup& group = thing.as<ObjectGroup>();
-        if (group.maybeUnboxedLayout()) {
-            for (size_t i = 0; i < seen.length(); i++) {
-                if (seen[i] == &group)
-                    return;
-            }
-            if (seen.append(&group) && worklist.append(&group)) {
-                return;
-            } else {
-                // If append fails, keep tracing normally. The worst that will
-                // happen is we end up overrecursing.
-            }
-        }
-    }
-
-    TraceChildren(this, thing.asCell(), thing.kind());
-}
-
 void
 gc::TraceCycleCollectorChildren(JS::CallbackTracer* trc, ObjectGroup* group)
 {
     MOZ_ASSERT(trc->isCallbackTracer());
 
-    // Early return if this group is not required to be in an ObjectGroup chain.
-    if (!group->maybeUnboxedLayout())
-        return group->traceChildren(trc);
-
-    ObjectGroupCycleCollectorTracer groupTracer(trc->asCallbackTracer());
-    group->traceChildren(&groupTracer);
-
-    while (!groupTracer.worklist.empty()) {
-        ObjectGroup* innerGroup = groupTracer.worklist.popCopy();
-        innerGroup->traceChildren(&groupTracer);
-    }
+    group->traceChildren(trc);
 }
 
-
+
 /*** Traced Edge Printer *************************************************************************/
 
 static size_t
diff --git a/js/src/gc/Zone.cpp b/js/src/gc/Zone.cpp
index ed099341c..f0cdde012 100644
--- a/js/src/gc/Zone.cpp
+++ b/js/src/gc/Zone.cpp
@@ -370,6 +370,21 @@ Zone::fixupAfterMovingGC()
     fixupInitialShapeTable();
 }
 
+bool
+Zone::addTypeDescrObject(JSContext* cx, HandleObject obj)
+{
+    // Type descriptor objects are always tenured so we don't need post barriers
+    // on the set.
+    MOZ_ASSERT(!IsInsideNursery(obj));
+    
+    if (!typeDescrObjects.put(obj)) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    
+    return true;
+}
+    
 ZoneList::ZoneList()
   : head(nullptr), tail(nullptr)
 {}
diff --git a/js/src/gc/Zone.h b/js/src/gc/Zone.h
index 50d06319d..c8520ed55 100644
--- a/js/src/gc/Zone.h
+++ b/js/src/gc/Zone.h
@@ -349,10 +349,17 @@ struct Zone : public JS::shadow::Zone,
     // Keep track of all TypeDescr and related objects in this compartment.
     // This is used by the GC to trace them all first when compacting, since the
     // TypedObject trace hook may access these objects.
-    using TypeDescrObjectSet = js::GCHashSet<js::HeapPtr<JSObject*>,
-                                             js::MovableCellHasher<js::HeapPtr<JSObject*>>,
+	
+     //
+     // There are no barriers here - the set contains only tenured objects so no
+     // post-barrier is required, and these are weak references so no pre-barrier
+     // is required.
+     using TypeDescrObjectSet = js::GCHashSet<JSObject*,
+                                             js::MovableCellHasher<JSObject*>,
                                              js::SystemAllocPolicy>;
     JS::WeakCache<TypeDescrObjectSet> typeDescrObjects;
+	
+    bool addTypeDescrObject(JSContext* cx, HandleObject obj);
 
 
     // Malloc counter to measure memory pressure for GC scheduling. It runs from
diff --git a/js/src/jit-test/tests/basic/unboxed-object-clear-new-script.js b/js/src/jit-test/tests/basic/unboxed-object-clear-new-script.js
deleted file mode 100644
index f55456222..000000000
--- a/js/src/jit-test/tests/basic/unboxed-object-clear-new-script.js
+++ /dev/null
@@ -1,49 +0,0 @@
-
-function Foo(a, b) {
-    this.a = a;
-    this.b = b;
-}
-
-function invalidate_foo() {
-    var a = [];
-    var counter = 0;
-    for (var i = 0; i < 50; i++)
-        a.push(new Foo(i, i + 1));
-    Object.defineProperty(Foo.prototype, "a", {configurable: true, set: function() { counter++; }});
-    for (var i = 0; i < 50; i++)
-        a.push(new Foo(i, i + 1));
-    delete Foo.prototype.a;
-    var total = 0;
-    for (var i = 0; i < a.length; i++) {
-        assertEq('a' in a[i], i < 50);
-        total += a[i].b;
-    }
-    assertEq(total, 2550);
-    assertEq(counter, 50);
-}
-invalidate_foo();
-
-function Bar(a, b, fn) {
-    this.a = a;
-    if (b == 30)
-        Object.defineProperty(Bar.prototype, "b", {configurable: true, set: fn});
-    this.b = b;
-}
-
-function invalidate_bar() {
-    var a = [];
-    var counter = 0;
-    function fn() { counter++; }
-    for (var i = 0; i < 50; i++)
-        a.push(new Bar(i, i + 1, fn));
-    delete Bar.prototype.b;
-    var total = 0;
-    for (var i = 0; i < a.length; i++) {
-        assertEq('a' in a[i], true);
-        assertEq('b' in a[i], i < 29);
-        total += a[i].a;
-    }
-    assertEq(total, 1225);
-    assertEq(counter, 21);
-}
-invalidate_bar();
diff --git a/js/src/jit-test/tests/basic/unboxed-object-convert-to-native.js b/js/src/jit-test/tests/basic/unboxed-object-convert-to-native.js
deleted file mode 100644
index 691fe166c..000000000
--- a/js/src/jit-test/tests/basic/unboxed-object-convert-to-native.js
+++ /dev/null
@@ -1,47 +0,0 @@
-
-// Test various ways of converting an unboxed object to native.
-
-function Foo(a, b) {
-    this.a = a;
-    this.b = b;
-}
-
-var proxyObj = {
-  get: function(recipient, name) {
-    return recipient[name] + 2;
-  }
-};
-
-function f() {
-    var a = [];
-    for (var i = 0; i < 50; i++)
-        a.push(new Foo(i, i + 1));
-
-    var prop = "a";
-
-    i = 0;
-    for (; i < 5; i++)
-        a[i].c = i;
-    for (; i < 10; i++)
-        Object.defineProperty(a[i], 'c', {value: i});
-    for (; i < 15; i++)
-        a[i] = new Proxy(a[i], proxyObj);
-    for (; i < 20; i++)
-        a[i].a = 3.5;
-    for (; i < 25; i++)
-        delete a[i].b;
-    for (; i < 30; i++)
-        a[prop] = 4;
-
-    var total = 0;
-    for (i = 0; i < a.length; i++) {
-        if ('a' in a[i])
-            total += a[i].a;
-        if ('b' in a[i])
-            total += a[i].b;
-        if ('c' in a[i])
-            total += a[i].c;
-    }
-    assertEq(total, 2382.5);
-}
-f();
diff --git a/js/src/jit-test/tests/basic/unboxed-object-getelem.js b/js/src/jit-test/tests/basic/unboxed-object-getelem.js
deleted file mode 100644
index b30b8325a..000000000
--- a/js/src/jit-test/tests/basic/unboxed-object-getelem.js
+++ /dev/null
@@ -1,20 +0,0 @@
-
-function f() {
-    var propNames = ["a","b","c","d","e","f","g","h","i","j","x","y"];
-    var arr = [];
-    for (var i=0; i<64; i++)
-	arr.push({x:1, y:2});
-    for (var i=0; i<64; i++) {
-        // Make sure there are expandos with dynamic slots for each object.
-        for (var j = 0; j < propNames.length; j++)
-            arr[i][propNames[j]] = j;
-    }
-    var res = 0;
-    for (var i=0; i<100000; i++) {
-	var o = arr[i % 64];
-	var p = propNames[i % propNames.length];
-	res += o[p];
-    }
-    assertEq(res, 549984);
-}
-f();
diff --git a/js/src/jit-test/tests/basic/unboxed-object-set-property.js b/js/src/jit-test/tests/basic/unboxed-object-set-property.js
deleted file mode 100644
index fdcfcf6b2..000000000
--- a/js/src/jit-test/tests/basic/unboxed-object-set-property.js
+++ /dev/null
@@ -1,31 +0,0 @@
-
-// Use the correct receiver when non-native objects are prototypes of other objects.
-
-function Thing(a, b) {
-    this.a = a;
-    this.b = b;
-}
-
-function foo() {
-    var array = [];
-    for (var i = 0; i < 10000; i++)
-        array.push(new Thing(i, i + 1));
-
-    var proto = new Thing(1, 2);
-    var obj = Object.create(proto);
-
-    Object.defineProperty(Thing.prototype, "c", {set:function() { this.d = 0; }});
-    obj.c = 3;
-    assertEq(obj.c, undefined);
-    assertEq(obj.d, 0);
-    assertEq(obj.hasOwnProperty("d"), true);
-    assertEq(proto.d, undefined);
-    assertEq(proto.hasOwnProperty("d"), false);
-
-    obj.a = 3;
-    assertEq(obj.a, 3);
-    assertEq(proto.a, 1);
-    assertEq(obj.hasOwnProperty("a"), true);
-}
-
-foo();
diff --git a/js/src/jit-test/tests/basic/unboxed-property-enumeration.js b/js/src/jit-test/tests/basic/unboxed-property-enumeration.js
deleted file mode 100644
index 142d932dd..000000000
--- a/js/src/jit-test/tests/basic/unboxed-property-enumeration.js
+++ /dev/null
@@ -1,24 +0,0 @@
-function O() {
-    this.x = 1;
-    this.y = 2;
-}
-function testUnboxed() {
-    var arr = [];
-    for (var i=0; i<100; i++)
-	arr.push(new O);
-
-    var o = arr[arr.length-1];
-    o[0] = 0;
-    o[2] = 2;
-    var sym = Symbol();
-    o[sym] = 1;
-    o.z = 3;
-    Object.defineProperty(o, '3', {value:1,enumerable:false,configurable:false,writable:false});
-    o[4] = 4;
-
-    var props = Reflect.ownKeys(o);
-    assertEq(props[props.length-1], sym);
-
-    assertEq(Object.getOwnPropertyNames(o).join(""), "0234xyz");
-}
-testUnboxed();
diff --git a/js/src/jit-test/tests/ion/unboxed-objects-invalidate.js b/js/src/jit-test/tests/ion/unboxed-objects-invalidate.js
deleted file mode 100644
index 02e27614f..000000000
--- a/js/src/jit-test/tests/ion/unboxed-objects-invalidate.js
+++ /dev/null
@@ -1,16 +0,0 @@
-
-var a = [];
-for (var i = 0; i < 2000; i++)
-    a.push({f:i});
-
-function f() {
-    var total = 0;
-    for (var i = 0; i < a.length; i++)
-        total += a[i].f;
-    return total;
-}
-assertEq(f(), 1999000);
-
-var sub = Object.create(a[0]);
-
-assertEq(f(), 1999000);
diff --git a/js/src/jit/AliasAnalysisShared.cpp b/js/src/jit/AliasAnalysisShared.cpp
index 81c0fd067..0f0d4a66a 100644
--- a/js/src/jit/AliasAnalysisShared.cpp
+++ b/js/src/jit/AliasAnalysisShared.cpp
@@ -93,10 +93,6 @@ GetObject(const MDefinition* ins)
       case MDefinition::Op_Elements:
       case MDefinition::Op_MaybeCopyElementsForWrite:
       case MDefinition::Op_MaybeToDoubleElement:
-      case MDefinition::Op_UnboxedArrayLength:
-      case MDefinition::Op_UnboxedArrayInitializedLength:
-      case MDefinition::Op_IncrementUnboxedArrayInitializedLength:
-      case MDefinition::Op_SetUnboxedArrayInitializedLength:
       case MDefinition::Op_TypedArrayLength:
       case MDefinition::Op_SetTypedObjectOffset:
       case MDefinition::Op_SetDisjointTypedElements:
@@ -114,8 +110,6 @@ GetObject(const MDefinition* ins)
       case MDefinition::Op_GuardObjectGroup:
       case MDefinition::Op_GuardObjectIdentity:
       case MDefinition::Op_GuardClass:
-      case MDefinition::Op_GuardUnboxedExpando:
-      case MDefinition::Op_LoadUnboxedExpando:
       case MDefinition::Op_LoadSlot:
       case MDefinition::Op_StoreSlot:
       case MDefinition::Op_InArray:
diff --git a/js/src/jit/BaselineCacheIR.cpp b/js/src/jit/BaselineCacheIR.cpp
index bf96932d1..67c80473b 100644
--- a/js/src/jit/BaselineCacheIR.cpp
+++ b/js/src/jit/BaselineCacheIR.cpp
@@ -16,7 +16,7 @@ using namespace js;
 using namespace js::jit;
 
 // OperandLocation represents the location of an OperandId. The operand is
-// either in a register or on the stack, and is either boxed or unboxed.
+// either in a register or on the stack.
 class OperandLocation
 {
   public:
@@ -787,9 +787,6 @@ BaselineCacheIRCompiler::emitGuardClass()
       case GuardClassKind::Array:
         clasp = &ArrayObject::class_;
         break;
-      case GuardClassKind::UnboxedArray:
-        clasp = &UnboxedArrayObject::class_;
-        break;
       case GuardClassKind::MappedArguments:
         clasp = &MappedArgumentsObject::class_;
         break;
@@ -818,36 +815,6 @@ BaselineCacheIRCompiler::emitGuardSpecificObject()
 }
 
 bool
-BaselineCacheIRCompiler::emitGuardNoUnboxedExpando()
-{
-    Register obj = allocator.useRegister(masm, reader.objOperandId());
-
-    FailurePath* failure;
-    if (!addFailurePath(&failure))
-        return false;
-
-    Address expandoAddr(obj, UnboxedPlainObject::offsetOfExpando());
-    masm.branchPtr(Assembler::NotEqual, expandoAddr, ImmWord(0), failure->label());
-    return true;
-}
-
-bool
-BaselineCacheIRCompiler::emitGuardAndLoadUnboxedExpando()
-{
-    Register obj = allocator.useRegister(masm, reader.objOperandId());
-    Register output = allocator.defineRegister(masm, reader.objOperandId());
-
-    FailurePath* failure;
-    if (!addFailurePath(&failure))
-        return false;
-
-    Address expandoAddr(obj, UnboxedPlainObject::offsetOfExpando());
-    masm.loadPtr(expandoAddr, output);
-    masm.branchTestPtr(Assembler::Zero, output, output, failure->label());
-    return true;
-}
-
-bool
 BaselineCacheIRCompiler::emitLoadFixedSlotResult()
 {
     Register obj = allocator.useRegister(masm, reader.objOperandId());
@@ -874,26 +841,6 @@ BaselineCacheIRCompiler::emitLoadDynamicSlotResult()
 }
 
 bool
-BaselineCacheIRCompiler::emitLoadUnboxedPropertyResult()
-{
-    Register obj = allocator.useRegister(masm, reader.objOperandId());
-    AutoScratchRegister scratch(allocator, masm);
-
-    JSValueType fieldType = reader.valueType();
-
-    Address fieldOffset(stubAddress(reader.stubOffset()));
-    masm.load32(fieldOffset, scratch);
-    masm.loadUnboxedProperty(BaseIndex(obj, scratch, TimesOne), fieldType, R0);
-
-    if (fieldType == JSVAL_TYPE_OBJECT)
-        emitEnterTypeMonitorIC();
-    else
-        emitReturnFromIC();
-
-    return true;
-}
-
-bool
 BaselineCacheIRCompiler::emitGuardNoDetachedTypedObjects()
 {
     FailurePath* failure;
@@ -1004,19 +951,6 @@ BaselineCacheIRCompiler::emitLoadInt32ArrayLengthResult()
 }
 
 bool
-BaselineCacheIRCompiler::emitLoadUnboxedArrayLengthResult()
-{
-    Register obj = allocator.useRegister(masm, reader.objOperandId());
-    masm.load32(Address(obj, UnboxedArrayObject::offsetOfLength()), R0.scratchReg());
-    masm.tagValue(JSVAL_TYPE_INT32, R0.scratchReg(), R0);
-
-    // The int32 type was monitored when attaching the stub, so we can
-    // just return.
-    emitReturnFromIC();
-    return true;
-}
-
-bool
 BaselineCacheIRCompiler::emitLoadArgumentsObjectLengthResult()
 {
     Register obj = allocator.useRegister(masm, reader.objOperandId());
diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index 3fa5a80ed..6b64bfb44 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -2049,13 +2049,7 @@ BaselineCompiler::emit_JSOP_NEWARRAY()
     return true;
 }
 
-bool
-BaselineCompiler::emit_JSOP_SPREADCALLARRAY()
-{
-    return emit_JSOP_NEWARRAY();
-}
-
-typedef JSObject* (*NewArrayCopyOnWriteFn)(JSContext*, HandleArrayObject, gc::InitialHeap);
+typedef ArrayObject* (*NewArrayCopyOnWriteFn)(JSContext*, HandleArrayObject, gc::InitialHeap);
 const VMFunction jit::NewArrayCopyOnWriteInfo =
     FunctionInfo<NewArrayCopyOnWriteFn>(js::NewDenseCopyOnWriteArray, "NewDenseCopyOnWriteArray");
 
@@ -4136,14 +4130,14 @@ BaselineCompiler::emit_JSOP_REST()
 {
     frame.syncStack(0);
 
-    JSObject* templateObject =
+    ArrayObject* templateObject =
         ObjectGroup::newArrayObject(cx, nullptr, 0, TenuredObject,
                                     ObjectGroup::NewArrayKind::UnknownIndex);
     if (!templateObject)
         return false;
 
     // Call IC.
-    ICRest_Fallback::Compiler compiler(cx, &templateObject->as<ArrayObject>());
+    ICRest_Fallback::Compiler compiler(cx, templateObject);
     if (!emitOpIC(compiler.getStub(&stubSpace_)))
         return false;
 
diff --git a/js/src/jit/BaselineCompiler.h b/js/src/jit/BaselineCompiler.h
index 6b5bf009e..910a52980 100644
--- a/js/src/jit/BaselineCompiler.h
+++ b/js/src/jit/BaselineCompiler.h
@@ -100,7 +100,6 @@ namespace jit {
     _(JSOP_BITNOT)             \
     _(JSOP_NEG)                \
     _(JSOP_NEWARRAY)           \
-    _(JSOP_SPREADCALLARRAY)    \
     _(JSOP_NEWARRAY_COPYONWRITE) \
     _(JSOP_INITELEM_ARRAY)     \
     _(JSOP_NEWOBJECT)          \
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index 863c61161..d95d08edc 100644
--- a/js/src/jit/BaselineIC.cpp
+++ b/js/src/jit/BaselineIC.cpp
@@ -42,8 +42,8 @@
 #include "jit/shared/Lowering-shared-inl.h"
 #include "vm/EnvironmentObject-inl.h"
 #include "vm/Interpreter-inl.h"
+#include "vm/NativeObject-inl.h"
 #include "vm/StringObject-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using mozilla::DebugOnly;
 
@@ -732,11 +732,6 @@ LastPropertyForSetProp(JSObject* obj)
     if (obj->isNative())
         return obj->as<NativeObject>().lastProperty();
 
-    if (obj->is<UnboxedPlainObject>()) {
-        UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando();
-        return expando ? expando->lastProperty() : nullptr;
-    }
-
     return nullptr;
 }
 
@@ -1153,56 +1148,6 @@ TryAttachNativeOrUnboxedGetValueElemStub(JSContext* cx, HandleScript script, jsb
 
     ICStub* monitorStub = stub->fallbackMonitorStub()->firstMonitorStub();
 
-    if (obj->is<UnboxedPlainObject>() && holder == obj) {
-        const UnboxedLayout::Property* property = obj->as<UnboxedPlainObject>().layout().lookup(id);
-
-        // Once unboxed objects support symbol-keys, we need to change the following accordingly
-        MOZ_ASSERT_IF(!keyVal.isString(), !property);
-
-        if (property) {
-            if (!cx->runtime()->jitSupportsFloatingPoint)
-                return true;
-
-            RootedPropertyName name(cx, JSID_TO_ATOM(id)->asPropertyName());
-            ICGetElemNativeCompiler<PropertyName*> compiler(cx, ICStub::GetElem_UnboxedPropertyName,
-                                                            monitorStub, obj, holder,
-                                                            name,
-                                                            ICGetElemNativeStub::UnboxedProperty,
-                                                            needsAtomize, property->offset +
-                                                            UnboxedPlainObject::offsetOfData(),
-                                                            property->type);
-            ICStub* newStub = compiler.getStub(compiler.getStubSpace(script));
-            if (!newStub)
-                return false;
-
-            stub->addNewStub(newStub);
-            *attached = true;
-            return true;
-        }
-
-        Shape* shape = obj->as<UnboxedPlainObject>().maybeExpando()->lookup(cx, id);
-        if (!shape->hasDefaultGetter() || !shape->hasSlot())
-            return true;
-
-        bool isFixedSlot;
-        uint32_t offset;
-        GetFixedOrDynamicSlotOffset(shape, &isFixedSlot, &offset);
-
-        ICGetElemNativeStub::AccessType acctype =
-            isFixedSlot ? ICGetElemNativeStub::FixedSlot
-                        : ICGetElemNativeStub::DynamicSlot;
-        ICGetElemNativeCompiler<T> compiler(cx, getGetElemStubKind<T>(ICStub::GetElem_NativeSlotName),
-                                            monitorStub, obj, holder, key,
-                                            acctype, needsAtomize, offset);
-        ICStub* newStub = compiler.getStub(compiler.getStubSpace(script));
-        if (!newStub)
-            return false;
-
-        stub->addNewStub(newStub);
-        *attached = true;
-        return true;
-    }
-
     if (!holder->isNative())
         return true;
 
@@ -1366,7 +1311,7 @@ IsNativeDenseElementAccess(HandleObject obj, HandleValue key)
 static bool
 IsNativeOrUnboxedDenseElementAccess(HandleObject obj, HandleValue key)
 {
-    if (!obj->isNative() && !obj->is<UnboxedArrayObject>())
+    if (!obj->isNative())
         return false;
     if (key.isInt32() && key.toInt32() >= 0 && !obj->is<TypedArrayObject>())
         return true;
@@ -1450,7 +1395,7 @@ TryAttachGetElemStub(JSContext* cx, JSScript* script, jsbytecode* pc, ICGetElem_
     }
 
     // Check for NativeObject[id] and UnboxedPlainObject[id] shape-optimizable accesses.
-    if (obj->isNative() || obj->is<UnboxedPlainObject>()) {
+    if (obj->isNative()) {
         RootedScript rootedScript(cx, script);
         if (rhs.isString()) {
             if (!TryAttachNativeOrUnboxedGetValueElemStub<PropertyName*>(cx, rootedScript, pc, stub,
@@ -1470,20 +1415,6 @@ TryAttachGetElemStub(JSContext* cx, JSScript* script, jsbytecode* pc, ICGetElem_
         script = rootedScript;
     }
 
-    // Check for UnboxedArray[int] accesses.
-    if (obj->is<UnboxedArrayObject>() && rhs.isInt32() && rhs.toInt32() >= 0) {
-        JitSpew(JitSpew_BaselineIC, "  Generating GetElem(UnboxedArray[Int32]) stub");
-        ICGetElem_UnboxedArray::Compiler compiler(cx, stub->fallbackMonitorStub()->firstMonitorStub(),
-                                                  obj->group());
-        ICStub* unboxedStub = compiler.getStub(compiler.getStubSpace(script));
-        if (!unboxedStub)
-            return false;
-
-        stub->addNewStub(unboxedStub);
-        *attached = true;
-        return true;
-    }
-
     // Check for TypedArray[int] => Number and TypedObject[int] => Number accesses.
     if ((obj->is<TypedArrayObject>() || IsPrimitiveArrayTypedObject(obj)) &&
         rhs.isNumber() &&
@@ -1876,14 +1807,6 @@ ICGetElemNativeCompiler<T>::generateStubCode(MacroAssembler& masm)
     Register holderReg;
     if (obj_ == holder_) {
         holderReg = objReg;
-
-        if (obj_->is<UnboxedPlainObject>() && acctype_ != ICGetElemNativeStub::UnboxedProperty) {
-            // The property will be loaded off the unboxed expando.
-            masm.push(R1.scratchReg());
-            popR1 = true;
-            holderReg = R1.scratchReg();
-            masm.loadPtr(Address(objReg, UnboxedPlainObject::offsetOfExpando()), holderReg);
-        }
     } else {
         // Shape guard holder.
         if (regs.empty()) {
@@ -1934,13 +1857,6 @@ ICGetElemNativeCompiler<T>::generateStubCode(MacroAssembler& masm)
         if (popR1)
             masm.addToStackPtr(ImmWord(sizeof(size_t)));
 
-    } else if (acctype_ == ICGetElemNativeStub::UnboxedProperty) {
-        masm.load32(Address(ICStubReg, ICGetElemNativeSlotStub<T>::offsetOfOffset()),
-                    scratchReg);
-        masm.loadUnboxedProperty(BaseIndex(objReg, scratchReg, TimesOne), unboxedType_,
-                                 TypedOrValueRegister(R0));
-        if (popR1)
-            masm.addToStackPtr(ImmWord(sizeof(size_t)));
     } else {
         MOZ_ASSERT(acctype_ == ICGetElemNativeStub::NativeGetter ||
                    acctype_ == ICGetElemNativeStub::ScriptedGetter);
@@ -2090,56 +2006,6 @@ ICGetElem_Dense::Compiler::generateStubCode(MacroAssembler& masm)
 }
 
 //
-// GetElem_UnboxedArray
-//
-
-bool
-ICGetElem_UnboxedArray::Compiler::generateStubCode(MacroAssembler& masm)
-{
-    MOZ_ASSERT(engine_ == Engine::Baseline);
-
-    Label failure;
-    masm.branchTestObject(Assembler::NotEqual, R0, &failure);
-    masm.branchTestInt32(Assembler::NotEqual, R1, &failure);
-
-    AllocatableGeneralRegisterSet regs(availableGeneralRegs(2));
-    Register scratchReg = regs.takeAny();
-
-    // Unbox R0 and group guard.
-    Register obj = masm.extractObject(R0, ExtractTemp0);
-    masm.loadPtr(Address(ICStubReg, ICGetElem_UnboxedArray::offsetOfGroup()), scratchReg);
-    masm.branchTestObjGroup(Assembler::NotEqual, obj, scratchReg, &failure);
-
-    // Unbox key.
-    Register key = masm.extractInt32(R1, ExtractTemp1);
-
-    // Bounds check.
-    masm.load32(Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()),
-                scratchReg);
-    masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), scratchReg);
-    masm.branch32(Assembler::BelowOrEqual, scratchReg, key, &failure);
-
-    // Load obj->elements.
-    masm.loadPtr(Address(obj, UnboxedArrayObject::offsetOfElements()), scratchReg);
-
-    // Load value.
-    size_t width = UnboxedTypeSize(elementType_);
-    BaseIndex addr(scratchReg, key, ScaleFromElemWidth(width));
-    masm.loadUnboxedProperty(addr, elementType_, R0);
-
-    // Only monitor the result if its type might change.
-    if (elementType_ == JSVAL_TYPE_OBJECT)
-        EmitEnterTypeMonitorIC(masm);
-    else
-        EmitReturnFromIC(masm);
-
-    // Failure case - jump to next stub
-    masm.bind(&failure);
-    EmitStubGuardFailure(masm);
-    return true;
-}
-
-//
 // GetElem_TypedArray
 //
 
@@ -2437,8 +2303,8 @@ CanOptimizeDenseOrUnboxedArraySetElem(JSObject* obj, uint32_t index,
                                       Shape* oldShape, uint32_t oldCapacity, uint32_t oldInitLength,
                                       bool* isAddingCaseOut, size_t* protoDepthOut)
 {
-    uint32_t initLength = GetAnyBoxedOrUnboxedInitializedLength(obj);
-    uint32_t capacity = GetAnyBoxedOrUnboxedCapacity(obj);
+    uint32_t initLength = obj->as<NativeObject>().getDenseInitializedLength();
+    uint32_t capacity = obj->as<NativeObject>().getDenseCapacity();
 
     *isAddingCaseOut = false;
     *protoDepthOut = 0;
@@ -2447,10 +2313,6 @@ CanOptimizeDenseOrUnboxedArraySetElem(JSObject* obj, uint32_t index,
     if (initLength < oldInitLength || capacity < oldCapacity)
         return false;
 
-    // Unboxed arrays need to be able to emit floating point code.
-    if (obj->is<UnboxedArrayObject>() && !obj->runtimeFromMainThread()->jitSupportsFloatingPoint)
-        return false;
-
     Shape* shape = obj->maybeShape();
 
     // Cannot optimize if the shape changed.
@@ -2532,8 +2394,8 @@ DoSetElemFallback(JSContext* cx, BaselineFrame* frame, ICSetElem_Fallback* stub_
     uint32_t oldCapacity = 0;
     uint32_t oldInitLength = 0;
     if (index.isInt32() && index.toInt32() >= 0) {
-        oldCapacity = GetAnyBoxedOrUnboxedCapacity(obj);
-        oldInitLength = GetAnyBoxedOrUnboxedInitializedLength(obj);
+        oldCapacity = obj->as<NativeObject>().getDenseCapacity();
+        oldInitLength = obj->as<NativeObject>().getDenseInitializedLength();
     }
 
     if (op == JSOP_INITELEM || op == JSOP_INITHIDDENELEM) {
@@ -2741,18 +2603,6 @@ BaselineScript::noteArrayWriteHole(uint32_t pcOffset)
 // SetElem_DenseOrUnboxedArray
 //
 
-template <typename T>
-void
-EmitUnboxedPreBarrierForBaseline(MacroAssembler &masm, T address, JSValueType type)
-{
-    if (type == JSVAL_TYPE_OBJECT)
-        EmitPreBarrier(masm, address, MIRType::Object);
-    else if (type == JSVAL_TYPE_STRING)
-        EmitPreBarrier(masm, address, MIRType::String);
-    else
-        MOZ_ASSERT(!UnboxedTypeNeedsPreBarrier(type));
-}
-
 bool
 ICSetElem_DenseOrUnboxedArray::Compiler::generateStubCode(MacroAssembler& masm)
 {
@@ -2871,29 +2721,6 @@ ICSetElem_DenseOrUnboxedArray::Compiler::generateStubCode(MacroAssembler& masm)
         masm.loadValue(valueAddr, tmpVal);
         EmitPreBarrier(masm, element, MIRType::Value);
         masm.storeValue(tmpVal, element);
-    } else {
-        // Set element on an unboxed array.
-
-        // Bounds check.
-        Address initLength(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-        masm.load32(initLength, scratchReg);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), scratchReg);
-        masm.branch32(Assembler::BelowOrEqual, scratchReg, key, &failure);
-
-        // Load obj->elements.
-        masm.loadPtr(Address(obj, UnboxedArrayObject::offsetOfElements()), scratchReg);
-
-        // Compute the address being written to.
-        BaseIndex address(scratchReg, key, ScaleFromElemWidth(UnboxedTypeSize(unboxedType_)));
-
-        EmitUnboxedPreBarrierForBaseline(masm, address, unboxedType_);
-
-        Address valueAddr(masm.getStackPointer(), ICStackValueOffset + sizeof(Value));
-        masm.Push(R0);
-        masm.loadValue(valueAddr, R0);
-        masm.storeUnboxedProperty(address, unboxedType_,
-                                  ConstantOrRegister(TypedOrValueRegister(R0)), &failurePopR0);
-        masm.Pop(R0);
     }
 
     EmitReturnFromIC(masm);
@@ -3087,40 +2914,6 @@ ICSetElemDenseOrUnboxedArrayAddCompiler::generateStubCode(MacroAssembler& masm)
         BaseIndex element(scratchReg, key, TimesEight);
         masm.loadValue(valueAddr, tmpVal);
         masm.storeValue(tmpVal, element);
-    } else {
-        // Adding element to an unboxed array.
-
-        // Bounds check (key == initLength)
-        Address initLengthAddr(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-        masm.load32(initLengthAddr, scratchReg);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), scratchReg);
-        masm.branch32(Assembler::NotEqual, scratchReg, key, &failure);
-
-        // Capacity check.
-        masm.checkUnboxedArrayCapacity(obj, RegisterOrInt32Constant(key), scratchReg, &failure);
-
-        // Load obj->elements.
-        masm.loadPtr(Address(obj, UnboxedArrayObject::offsetOfElements()), scratchReg);
-
-        // Write the value first, since this can fail. No need for pre-barrier
-        // since we're not overwriting an old value.
-        masm.Push(R0);
-        Address valueAddr(masm.getStackPointer(), ICStackValueOffset + sizeof(Value));
-        masm.loadValue(valueAddr, R0);
-        BaseIndex address(scratchReg, key, ScaleFromElemWidth(UnboxedTypeSize(unboxedType_)));
-        masm.storeUnboxedProperty(address, unboxedType_,
-                                  ConstantOrRegister(TypedOrValueRegister(R0)), &failurePopR0);
-        masm.Pop(R0);
-
-        // Increment initialized length.
-        masm.add32(Imm32(1), initLengthAddr);
-
-        // If length is now <= key, increment length.
-        Address lengthAddr(obj, UnboxedArrayObject::offsetOfLength());
-        Label skipIncrementLength;
-        masm.branch32(Assembler::Above, lengthAddr, key, &skipIncrementLength);
-        masm.add32(Imm32(1), lengthAddr);
-        masm.bind(&skipIncrementLength);
     }
 
     EmitReturnFromIC(masm);
@@ -4256,18 +4049,7 @@ TryAttachSetValuePropStub(JSContext* cx, HandleScript script, jsbytecode* pc, IC
         return true;
 
     if (!obj->isNative()) {
-        if (obj->is<UnboxedPlainObject>()) {
-            UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando();
-            if (expando) {
-                shape = expando->lookup(cx, name);
-                if (!shape)
-                    return true;
-            } else {
-                return true;
-            }
-        } else {
-            return true;
-        }
+        return true;
     }
 
     size_t chainDepth;
@@ -4418,40 +4200,6 @@ TryAttachSetAccessorPropStub(JSContext* cx, HandleScript script, jsbytecode* pc,
 }
 
 static bool
-TryAttachUnboxedSetPropStub(JSContext* cx, HandleScript script,
-                            ICSetProp_Fallback* stub, HandleId id,
-                            HandleObject obj, HandleValue rhs, bool* attached)
-{
-    MOZ_ASSERT(!*attached);
-
-    if (!cx->runtime()->jitSupportsFloatingPoint)
-        return true;
-
-    if (!obj->is<UnboxedPlainObject>())
-        return true;
-
-    const UnboxedLayout::Property* property = obj->as<UnboxedPlainObject>().layout().lookup(id);
-    if (!property)
-        return true;
-
-    ICSetProp_Unboxed::Compiler compiler(cx, obj->group(),
-                                         property->offset + UnboxedPlainObject::offsetOfData(),
-                                         property->type);
-    ICUpdatedStub* newStub = compiler.getStub(compiler.getStubSpace(script));
-    if (!newStub)
-        return false;
-    if (compiler.needsUpdateStubs() && !newStub->addUpdateStubForValue(cx, script, obj, id, rhs))
-        return false;
-
-    stub->addNewStub(newStub);
-
-    StripPreliminaryObjectStubs(cx, stub);
-
-    *attached = true;
-    return true;
-}
-
-static bool
 TryAttachTypedObjectSetPropStub(JSContext* cx, HandleScript script,
                                 ICSetProp_Fallback* stub, HandleId id,
                                 HandleObject obj, HandleValue rhs, bool* attached)
@@ -4534,12 +4282,6 @@ DoSetPropFallback(JSContext* cx, BaselineFrame* frame, ICSetProp_Fallback* stub_
         return false;
     RootedReceiverGuard oldGuard(cx, ReceiverGuard(obj));
 
-    if (obj->is<UnboxedPlainObject>()) {
-        MOZ_ASSERT(!oldShape);
-        if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando())
-            oldShape = expando->lastProperty();
-    }
-
     bool attached = false;
     // There are some reasons we can fail to attach a stub that are temporary.
     // We want to avoid calling noteUnoptimizableAccess() if the reason we
@@ -4612,15 +4354,6 @@ DoSetPropFallback(JSContext* cx, BaselineFrame* frame, ICSetProp_Fallback* stub_
 
     if (!attached &&
         lhs.isObject() &&
-        !TryAttachUnboxedSetPropStub(cx, script, stub, id, obj, rhs, &attached))
-    {
-        return false;
-    }
-    if (attached)
-        return true;
-
-    if (!attached &&
-        lhs.isObject() &&
         !TryAttachTypedObjectSetPropStub(cx, script, stub, id, obj, rhs, &attached))
     {
         return false;
@@ -4703,20 +4436,7 @@ GuardGroupAndShapeMaybeUnboxedExpando(MacroAssembler& masm, JSObject* obj,
 
     // Guard against shape or expando shape.
     masm.loadPtr(Address(ICStubReg, offsetOfShape), scratch);
-    if (obj->is<UnboxedPlainObject>()) {
-        Address expandoAddress(object, UnboxedPlainObject::offsetOfExpando());
-        masm.branchPtr(Assembler::Equal, expandoAddress, ImmWord(0), failure);
-        Label done;
-        masm.push(object);
-        masm.loadPtr(expandoAddress, object);
-        masm.branchTestObjShape(Assembler::Equal, object, scratch, &done);
-        masm.pop(object);
-        masm.jump(failure);
-        masm.bind(&done);
-        masm.pop(object);
-    } else {
-        masm.branchTestObjShape(Assembler::NotEqual, object, scratch, failure);
-    }
+    masm.branchTestObjShape(Assembler::NotEqual, object, scratch, failure);
 }
 
 bool
@@ -4755,13 +4475,7 @@ ICSetProp_Native::Compiler::generateStubCode(MacroAssembler& masm)
     regs.takeUnchecked(objReg);
 
     Register holderReg;
-    if (obj_->is<UnboxedPlainObject>()) {
-        // We are loading off the expando object, so use that for the holder.
-        holderReg = regs.takeAny();
-        masm.loadPtr(Address(objReg, UnboxedPlainObject::offsetOfExpando()), holderReg);
-        if (!isFixedSlot_)
-            masm.loadPtr(Address(holderReg, NativeObject::offsetOfSlots()), holderReg);
-    } else if (isFixedSlot_) {
+    if (isFixedSlot_) {
         holderReg = objReg;
     } else {
         holderReg = regs.takeAny();
@@ -4898,31 +4612,17 @@ ICSetPropNativeAddCompiler::generateStubCode(MacroAssembler& masm)
     regs.add(R0);
     regs.takeUnchecked(objReg);
 
-    if (obj_->is<UnboxedPlainObject>()) {
-        holderReg = regs.takeAny();
-        masm.loadPtr(Address(objReg, UnboxedPlainObject::offsetOfExpando()), holderReg);
-
-        // Write the expando object's new shape.
-        Address shapeAddr(holderReg, ShapedObject::offsetOfShape());
-        EmitPreBarrier(masm, shapeAddr, MIRType::Shape);
-        masm.loadPtr(Address(ICStubReg, ICSetProp_NativeAdd::offsetOfNewShape()), scratch);
-        masm.storePtr(scratch, shapeAddr);
+    // Write the object's new shape.
+    Address shapeAddr(objReg, ShapedObject::offsetOfShape());
+    EmitPreBarrier(masm, shapeAddr, MIRType::Shape);
+    masm.loadPtr(Address(ICStubReg, ICSetProp_NativeAdd::offsetOfNewShape()), scratch);
+    masm.storePtr(scratch, shapeAddr);
 
-        if (!isFixedSlot_)
-            masm.loadPtr(Address(holderReg, NativeObject::offsetOfSlots()), holderReg);
+    if (isFixedSlot_) {
+        holderReg = objReg;
     } else {
-        // Write the object's new shape.
-        Address shapeAddr(objReg, ShapedObject::offsetOfShape());
-        EmitPreBarrier(masm, shapeAddr, MIRType::Shape);
-        masm.loadPtr(Address(ICStubReg, ICSetProp_NativeAdd::offsetOfNewShape()), scratch);
-        masm.storePtr(scratch, shapeAddr);
-
-        if (isFixedSlot_) {
-            holderReg = objReg;
-        } else {
-            holderReg = regs.takeAny();
-            masm.loadPtr(Address(objReg, NativeObject::offsetOfSlots()), holderReg);
-        }
+        holderReg = regs.takeAny();
+        masm.loadPtr(Address(objReg, NativeObject::offsetOfSlots()), holderReg);
     }
 
     // Perform the store.  No write barrier required since this is a new
@@ -4954,70 +4654,6 @@ ICSetPropNativeAddCompiler::generateStubCode(MacroAssembler& masm)
 }
 
 bool
-ICSetProp_Unboxed::Compiler::generateStubCode(MacroAssembler& masm)
-{
-    MOZ_ASSERT(engine_ == Engine::Baseline);
-
-    Label failure;
-
-    // Guard input is an object.
-    masm.branchTestObject(Assembler::NotEqual, R0, &failure);
-
-    AllocatableGeneralRegisterSet regs(availableGeneralRegs(2));
-    Register scratch = regs.takeAny();
-
-    // Unbox and group guard.
-    Register object = masm.extractObject(R0, ExtractTemp0);
-    masm.loadPtr(Address(ICStubReg, ICSetProp_Unboxed::offsetOfGroup()), scratch);
-    masm.branchPtr(Assembler::NotEqual, Address(object, JSObject::offsetOfGroup()), scratch,
-                   &failure);
-
-    if (needsUpdateStubs()) {
-        // Stow both R0 and R1 (object and value).
-        EmitStowICValues(masm, 2);
-
-        // Move RHS into R0 for TypeUpdate check.
-        masm.moveValue(R1, R0);
-
-        // Call the type update stub.
-        if (!callTypeUpdateIC(masm, sizeof(Value)))
-            return false;
-
-        // Unstow R0 and R1 (object and key)
-        EmitUnstowICValues(masm, 2);
-
-        // The TypeUpdate IC may have smashed object. Rederive it.
-        masm.unboxObject(R0, object);
-
-        // Trigger post barriers here on the values being written. Fields which
-        // objects can be written to also need update stubs.
-        LiveGeneralRegisterSet saveRegs;
-        saveRegs.add(R0);
-        saveRegs.add(R1);
-        saveRegs.addUnchecked(object);
-        saveRegs.add(ICStubReg);
-        emitPostWriteBarrierSlot(masm, object, R1, scratch, saveRegs);
-    }
-
-    // Compute the address being written to.
-    masm.load32(Address(ICStubReg, ICSetProp_Unboxed::offsetOfFieldOffset()), scratch);
-    BaseIndex address(object, scratch, TimesOne);
-
-    EmitUnboxedPreBarrierForBaseline(masm, address, fieldType_);
-    masm.storeUnboxedProperty(address, fieldType_,
-                              ConstantOrRegister(TypedOrValueRegister(R1)), &failure);
-
-    // The RHS has to be in R0.
-    masm.moveValue(R1, R0);
-
-    EmitReturnFromIC(masm);
-
-    masm.bind(&failure);
-    EmitStubGuardFailure(masm);
-    return true;
-}
-
-bool
 ICSetProp_TypedObject::Compiler::generateStubCode(MacroAssembler& masm)
 {
     MOZ_ASSERT(engine_ == Engine::Baseline);
@@ -5490,13 +5126,6 @@ GetTemplateObjectForSimd(JSContext* cx, JSFunction* target, MutableHandleObject
     return true;
 }
 
-static void
-EnsureArrayGroupAnalyzed(JSContext* cx, JSObject* obj)
-{
-    if (PreliminaryObjectArrayWithTemplate* objects = obj->group()->maybePreliminaryObjects())
-        objects->maybeAnalyze(cx, obj->group(), /* forceAnalyze = */ true);
-}
-
 static bool
 GetTemplateObjectForNative(JSContext* cx, HandleFunction target, const CallArgs& args,
                            MutableHandleObject res, bool* skipAttach)
@@ -5528,10 +5157,7 @@ GetTemplateObjectForNative(JSContext* cx, HandleFunction target, const CallArgs&
             // With this and other array templates, analyze the group so that
             // we don't end up with a template whose structure might change later.
             res.set(NewFullyAllocatedArrayForCallingAllocationSite(cx, count, TenuredObject));
-            if (!res)
-                return false;
-            EnsureArrayGroupAnalyzed(cx, res);
-            return true;
+            return !!res;
         }
     }
 
@@ -5557,10 +5183,7 @@ GetTemplateObjectForNative(JSContext* cx, HandleFunction target, const CallArgs&
                 }
                 res.set(NewFullyAllocatedArrayTryReuseGroup(cx, &args.thisv().toObject(), 0,
                                                             TenuredObject));
-                if (!res)
-                    return false;
-                EnsureArrayGroupAnalyzed(cx, res);
-                return true;
+                return !!res;
             }
         }
     }
@@ -5577,10 +5200,7 @@ GetTemplateObjectForNative(JSContext* cx, HandleFunction target, const CallArgs&
         }
 
         res.set(NewFullyAllocatedArrayForCallingAllocationSite(cx, 0, TenuredObject));
-        if (!res)
-            return false;
-        EnsureArrayGroupAnalyzed(cx, res);
-        return true;
+        return !!res;
     }
 
     if (native == StringConstructor) {
@@ -5793,7 +5413,7 @@ TryAttachCallStub(JSContext* cx, ICCall_Fallback* stub, HandleScript script, jsb
             if (!thisObject)
                 return false;
 
-            if (thisObject->is<PlainObject>() || thisObject->is<UnboxedPlainObject>())
+            if (thisObject->is<PlainObject>())
                 templateObject = thisObject;
         }
 
@@ -5887,15 +5507,24 @@ TryAttachCallStub(JSContext* cx, ICCall_Fallback* stub, HandleScript script, jsb
 }
 
 static bool
-CopyArray(JSContext* cx, HandleObject obj, MutableHandleValue result)
+CopyArray(JSContext* cx, HandleArrayObject arr, MutableHandleValue result)
 {
-    uint32_t length = GetAnyBoxedOrUnboxedArrayLength(obj);
-    JSObject* nobj = NewFullyAllocatedArrayTryReuseGroup(cx, obj, length, TenuredObject);
+    uint32_t length = arr->length();
+    ArrayObject* nobj = NewFullyAllocatedArrayTryReuseGroup(cx, arr, length, TenuredObject);
     if (!nobj)
         return false;
-    EnsureArrayGroupAnalyzed(cx, nobj);
-    CopyAnyBoxedOrUnboxedDenseElements(cx, nobj, obj, 0, 0, length);
-
+    
+    MOZ_ASSERT(arr->isNative());
+    MOZ_ASSERT(nobj->isNative());
+    MOZ_ASSERT(nobj->as<NativeObject>().getDenseInitializedLength() == 0);
+    MOZ_ASSERT(arr->as<NativeObject>().getDenseInitializedLength() >= length);
+    MOZ_ASSERT(nobj->as<NativeObject>().getDenseCapacity() >= length);
+
+    nobj->as<NativeObject>().setDenseInitializedLength(length);
+
+    const Value* vp = arr->as<NativeObject>().getDenseElements();
+    nobj->as<NativeObject>().initDenseElements(0, vp, length);
+    
     result.setObject(*nobj);
     return true;
 }
@@ -5926,26 +5555,22 @@ TryAttachStringSplit(JSContext* cx, ICCall_Fallback* stub, HandleScript script,
     RootedValue arr(cx);
 
     // Copy the array before storing in stub.
-    if (!CopyArray(cx, obj, &arr))
+    if (!CopyArray(cx, obj.as<ArrayObject>(), &arr))
         return false;
 
     // Atomize all elements of the array.
-    RootedObject arrObj(cx, &arr.toObject());
-    uint32_t initLength = GetAnyBoxedOrUnboxedArrayLength(arrObj);
+    RootedArrayObject arrObj(cx, &arr.toObject().as<ArrayObject>());
+    uint32_t initLength = arrObj->length();
     for (uint32_t i = 0; i < initLength; i++) {
-        JSAtom* str = js::AtomizeString(cx, GetAnyBoxedOrUnboxedDenseElement(arrObj, i).toString());
+        JSAtom* str = js::AtomizeString(cx, arrObj->getDenseElement(i).toString());
         if (!str)
             return false;
 
-        if (!SetAnyBoxedOrUnboxedDenseElement(cx, arrObj, i, StringValue(str))) {
-            // The value could not be stored to an unboxed dense element.
-            return true;
-        }
+        arrObj->setDenseElementWithType(cx, i, StringValue(str));
     }
 
     ICCall_StringSplit::Compiler compiler(cx, stub->fallbackMonitorStub()->firstMonitorStub(),
-                                          script->pcToOffset(pc), str, sep,
-                                          arr);
+                                          script->pcToOffset(pc), str, sep, arrObj);
     ICStub* newStub = compiler.getStub(compiler.getStubSpace(script));
     if (!newStub)
         return false;
@@ -6830,7 +6455,7 @@ ICCallScriptedCompiler::generateStubCode(MacroAssembler& masm)
     return true;
 }
 
-typedef bool (*CopyArrayFn)(JSContext*, HandleObject, MutableHandleValue);
+typedef bool (*CopyArrayFn)(JSContext*, HandleArrayObject, MutableHandleValue);
 static const VMFunction CopyArrayInfo = FunctionInfo<CopyArrayFn>(CopyArray, "CopyArray");
 
 bool
@@ -8301,19 +7926,6 @@ ICGetElem_Dense::Clone(JSContext* cx, ICStubSpace* space, ICStub* firstMonitorSt
     return New<ICGetElem_Dense>(cx, space, other.jitCode(), firstMonitorStub, other.shape_);
 }
 
-ICGetElem_UnboxedArray::ICGetElem_UnboxedArray(JitCode* stubCode, ICStub* firstMonitorStub,
-                                               ObjectGroup *group)
-  : ICMonitoredStub(GetElem_UnboxedArray, stubCode, firstMonitorStub),
-    group_(group)
-{ }
-
-/* static */ ICGetElem_UnboxedArray*
-ICGetElem_UnboxedArray::Clone(JSContext* cx, ICStubSpace* space, ICStub* firstMonitorStub,
-                              ICGetElem_UnboxedArray& other)
-{
-    return New<ICGetElem_UnboxedArray>(cx, space, other.jitCode(), firstMonitorStub, other.group_);
-}
-
 ICGetElem_TypedArray::ICGetElem_TypedArray(JitCode* stubCode, Shape* shape, Scalar::Type type)
   : ICStub(GetElem_TypedArray, stubCode),
     shape_(shape)
@@ -8689,8 +8301,8 @@ static bool DoRestFallback(JSContext* cx, BaselineFrame* frame, ICRest_Fallback*
     unsigned numRest = numActuals > numFormals ? numActuals - numFormals : 0;
     Value* rest = frame->argv() + numFormals;
 
-    JSObject* obj = ObjectGroup::newArrayObject(cx, rest, numRest, GenericObject,
-                                                ObjectGroup::NewArrayKind::UnknownIndex);
+    ArrayObject* obj = ObjectGroup::newArrayObject(cx, rest, numRest, GenericObject,
+                                                   ObjectGroup::NewArrayKind::UnknownIndex);
     if (!obj)
         return false;
     res.setObject(*obj);
diff --git a/js/src/jit/BaselineIC.h b/js/src/jit/BaselineIC.h
index a57556d99..98f0e1c59 100644
--- a/js/src/jit/BaselineIC.h
+++ b/js/src/jit/BaselineIC.h
@@ -22,7 +22,6 @@
 #include "jit/SharedICRegisters.h"
 #include "js/GCVector.h"
 #include "vm/ArrayObject.h"
-#include "vm/UnboxedObject.h"
 
 namespace js {
 namespace jit {
@@ -892,54 +891,6 @@ class ICGetElem_Dense : public ICMonitoredStub
     };
 };
 
-class ICGetElem_UnboxedArray : public ICMonitoredStub
-{
-    friend class ICStubSpace;
-
-    GCPtrObjectGroup group_;
-
-    ICGetElem_UnboxedArray(JitCode* stubCode, ICStub* firstMonitorStub, ObjectGroup* group);
-
-  public:
-    static ICGetElem_UnboxedArray* Clone(JSContext* cx, ICStubSpace* space,
-                                         ICStub* firstMonitorStub, ICGetElem_UnboxedArray& other);
-
-    static size_t offsetOfGroup() {
-        return offsetof(ICGetElem_UnboxedArray, group_);
-    }
-
-    GCPtrObjectGroup& group() {
-        return group_;
-    }
-
-    class Compiler : public ICStubCompiler {
-      ICStub* firstMonitorStub_;
-      RootedObjectGroup group_;
-      JSValueType elementType_;
-
-      protected:
-        MOZ_MUST_USE bool generateStubCode(MacroAssembler& masm);
-
-        virtual int32_t getKey() const {
-            return static_cast<int32_t>(engine_) |
-                  (static_cast<int32_t>(kind) << 1) |
-                  (static_cast<int32_t>(elementType_) << 17);
-        }
-
-      public:
-        Compiler(JSContext* cx, ICStub* firstMonitorStub, ObjectGroup* group)
-          : ICStubCompiler(cx, ICStub::GetElem_UnboxedArray, Engine::Baseline),
-            firstMonitorStub_(firstMonitorStub),
-            group_(cx, group),
-            elementType_(group->unboxedLayoutDontCheckGeneration().elementType())
-        {}
-
-        ICStub* getStub(ICStubSpace* space) {
-            return newStub<ICGetElem_UnboxedArray>(space, getStubCode(), firstMonitorStub_, group_);
-        }
-    };
-};
-
 // Accesses scalar elements of a typed array or typed object.
 class ICGetElem_TypedArray : public ICStub
 {
@@ -1115,9 +1066,7 @@ class ICSetElem_DenseOrUnboxedArray : public ICUpdatedStub
           : ICStubCompiler(cx, ICStub::SetElem_DenseOrUnboxedArray, Engine::Baseline),
             shape_(cx, shape),
             group_(cx, group),
-            unboxedType_(shape
-                         ? JSVAL_TYPE_MAGIC
-                         : group->unboxedLayoutDontCheckGeneration().elementType())
+            unboxedType_(JSVAL_TYPE_MAGIC)
         {}
 
         ICUpdatedStub* getStub(ICStubSpace* space) {
@@ -1225,9 +1174,7 @@ class ICSetElemDenseOrUnboxedArrayAddCompiler : public ICStubCompiler {
         : ICStubCompiler(cx, ICStub::SetElem_DenseOrUnboxedArrayAdd, Engine::Baseline),
           obj_(cx, obj),
           protoChainDepth_(protoChainDepth),
-          unboxedType_(obj->is<UnboxedArrayObject>()
-                       ? obj->as<UnboxedArrayObject>().elementType()
-                       : JSVAL_TYPE_MAGIC)
+          unboxedType_(JSVAL_TYPE_MAGIC)
     {}
 
     template <size_t ProtoChainDepth>
@@ -1875,8 +1822,7 @@ class ICSetProp_Native : public ICUpdatedStub
         virtual int32_t getKey() const {
             return static_cast<int32_t>(engine_) |
                   (static_cast<int32_t>(kind) << 1) |
-                  (static_cast<int32_t>(isFixedSlot_) << 17) |
-                  (static_cast<int32_t>(obj_->is<UnboxedPlainObject>()) << 18);
+                  (static_cast<int32_t>(isFixedSlot_) << 17);
         }
 
         MOZ_MUST_USE bool generateStubCode(MacroAssembler& masm);
@@ -1981,7 +1927,6 @@ class ICSetPropNativeAddCompiler : public ICStubCompiler
         return static_cast<int32_t>(engine_) |
               (static_cast<int32_t>(kind) << 1) |
               (static_cast<int32_t>(isFixedSlot_) << 17) |
-              (static_cast<int32_t>(obj_->is<UnboxedPlainObject>()) << 18) |
               (static_cast<int32_t>(protoChainDepth_) << 19);
     }
 
@@ -2006,10 +1951,7 @@ class ICSetPropNativeAddCompiler : public ICStubCompiler
             newGroup = nullptr;
 
         RootedShape newShape(cx);
-        if (obj_->isNative())
-            newShape = obj_->as<NativeObject>().lastProperty();
-        else
-            newShape = obj_->as<UnboxedPlainObject>().maybeExpando()->lastProperty();
+        newShape = obj_->as<NativeObject>().lastProperty();
 
         return newStub<ICSetProp_NativeAddImpl<ProtoChainDepth>>(
             space, getStubCode(), oldGroup_, shapes, newShape, newGroup, offset_);
@@ -2870,10 +2812,10 @@ class ICCall_StringSplit : public ICMonitoredStub
     uint32_t pcOffset_;
     GCPtrString expectedStr_;
     GCPtrString expectedSep_;
-    GCPtrObject templateObject_;
+    GCPtrArrayObject templateObject_;
 
     ICCall_StringSplit(JitCode* stubCode, ICStub* firstMonitorStub, uint32_t pcOffset, JSString* str,
-                       JSString* sep, JSObject* templateObject)
+                       JSString* sep, ArrayObject* templateObject)
       : ICMonitoredStub(ICStub::Call_StringSplit, stubCode, firstMonitorStub),
         pcOffset_(pcOffset), expectedStr_(str), expectedSep_(sep),
         templateObject_(templateObject)
@@ -2900,7 +2842,7 @@ class ICCall_StringSplit : public ICMonitoredStub
         return expectedSep_;
     }
 
-    GCPtrObject& templateObject() {
+    GCPtrArrayObject& templateObject() {
         return templateObject_;
     }
 
@@ -2910,7 +2852,7 @@ class ICCall_StringSplit : public ICMonitoredStub
         uint32_t pcOffset_;
         RootedString expectedStr_;
         RootedString expectedSep_;
-        RootedObject templateObject_;
+        RootedArrayObject templateObject_;
 
         MOZ_MUST_USE bool generateStubCode(MacroAssembler& masm);
 
@@ -2921,13 +2863,13 @@ class ICCall_StringSplit : public ICMonitoredStub
 
       public:
         Compiler(JSContext* cx, ICStub* firstMonitorStub, uint32_t pcOffset, HandleString str,
-                 HandleString sep, HandleValue templateObject)
+                 HandleString sep, HandleArrayObject templateObject)
           : ICCallStubCompiler(cx, ICStub::Call_StringSplit),
             firstMonitorStub_(firstMonitorStub),
             pcOffset_(pcOffset),
             expectedStr_(cx, str),
             expectedSep_(cx, sep),
-            templateObject_(cx, &templateObject.toObject())
+            templateObject_(cx, templateObject)
         { }
 
         ICStub* getStub(ICStubSpace* space) {
diff --git a/js/src/jit/BaselineInspector.cpp b/js/src/jit/BaselineInspector.cpp
index c9e09bed7..3b852debf 100644
--- a/js/src/jit/BaselineInspector.cpp
+++ b/js/src/jit/BaselineInspector.cpp
@@ -96,32 +96,19 @@ VectorAppendNoDuplicate(S& list, T value)
 
 static bool
 AddReceiver(const ReceiverGuard& receiver,
-            BaselineInspector::ReceiverVector& receivers,
-            BaselineInspector::ObjectGroupVector& convertUnboxedGroups)
+            BaselineInspector::ReceiverVector& receivers)
 {
-    if (receiver.group && receiver.group->maybeUnboxedLayout()) {
-        if (receiver.group->unboxedLayout().nativeGroup())
-            return VectorAppendNoDuplicate(convertUnboxedGroups, receiver.group);
-    }
     return VectorAppendNoDuplicate(receivers, receiver);
 }
 
 static bool
 GetCacheIRReceiverForNativeReadSlot(ICCacheIR_Monitored* stub, ReceiverGuard* receiver)
 {
-    // We match either:
+    // We match:
     //
     //   GuardIsObject 0
     //   GuardShape 0
     //   LoadFixedSlotResult 0 or LoadDynamicSlotResult 0
-    //
-    // or
-    //
-    //   GuardIsObject 0
-    //   GuardGroup 0
-    //   1: GuardAndLoadUnboxedExpando 0
-    //   GuardShape 1
-    //   LoadFixedSlotResult 1 or LoadDynamicSlotResult 1
 
     *receiver = ReceiverGuard();
     CacheIRReader reader(stub->stubInfo());
@@ -130,14 +117,6 @@ GetCacheIRReceiverForNativeReadSlot(ICCacheIR_Monitored* stub, ReceiverGuard* re
     if (!reader.matchOp(CacheOp::GuardIsObject, objId))
         return false;
 
-    if (reader.matchOp(CacheOp::GuardGroup, objId)) {
-        receiver->group = stub->stubInfo()->getStubField<ObjectGroup*>(stub, reader.stubOffset());
-
-        if (!reader.matchOp(CacheOp::GuardAndLoadUnboxedExpando, objId))
-            return false;
-        objId = reader.objOperandId();
-    }
-
     if (reader.matchOp(CacheOp::GuardShape, objId)) {
         receiver->shape = stub->stubInfo()->getStubField<Shape*>(stub, reader.stubOffset());
         return reader.matchOpEither(CacheOp::LoadFixedSlotResult, CacheOp::LoadDynamicSlotResult);
@@ -146,40 +125,13 @@ GetCacheIRReceiverForNativeReadSlot(ICCacheIR_Monitored* stub, ReceiverGuard* re
     return false;
 }
 
-static bool
-GetCacheIRReceiverForUnboxedProperty(ICCacheIR_Monitored* stub, ReceiverGuard* receiver)
-{
-    // We match:
-    //
-    //   GuardIsObject 0
-    //   GuardGroup 0
-    //   LoadUnboxedPropertyResult 0 ..
-
-    *receiver = ReceiverGuard();
-    CacheIRReader reader(stub->stubInfo());
-
-    ObjOperandId objId = ObjOperandId(0);
-    if (!reader.matchOp(CacheOp::GuardIsObject, objId))
-        return false;
-
-    if (!reader.matchOp(CacheOp::GuardGroup, objId))
-        return false;
-    receiver->group = stub->stubInfo()->getStubField<ObjectGroup*>(stub, reader.stubOffset());
-
-    return reader.matchOp(CacheOp::LoadUnboxedPropertyResult, objId);
-}
-
 bool
-BaselineInspector::maybeInfoForPropertyOp(jsbytecode* pc, ReceiverVector& receivers,
-                                          ObjectGroupVector& convertUnboxedGroups)
+BaselineInspector::maybeInfoForPropertyOp(jsbytecode* pc, ReceiverVector& receivers)
 {
     // Return a list of the receivers seen by the baseline IC for the current
     // op. Empty lists indicate no receivers are known, or there was an
-    // uncacheable access. convertUnboxedGroups is used for unboxed object
-    // groups which have been seen, but have had instances converted to native
-    // objects and should be eagerly converted by Ion.
+    // uncacheable access.
     MOZ_ASSERT(receivers.empty());
-    MOZ_ASSERT(convertUnboxedGroups.empty());
 
     if (!hasBaselineScript())
         return true;
@@ -191,8 +143,7 @@ BaselineInspector::maybeInfoForPropertyOp(jsbytecode* pc, ReceiverVector& receiv
     while (stub->next()) {
         ReceiverGuard receiver;
         if (stub->isCacheIR_Monitored()) {
-            if (!GetCacheIRReceiverForNativeReadSlot(stub->toCacheIR_Monitored(), &receiver) &&
-                !GetCacheIRReceiverForUnboxedProperty(stub->toCacheIR_Monitored(), &receiver))
+            if (!GetCacheIRReceiverForNativeReadSlot(stub->toCacheIR_Monitored(), &receiver))
             {
                 receivers.clear();
                 return true;
@@ -200,14 +151,12 @@ BaselineInspector::maybeInfoForPropertyOp(jsbytecode* pc, ReceiverVector& receiv
         } else if (stub->isSetProp_Native()) {
             receiver = ReceiverGuard(stub->toSetProp_Native()->group(),
                                      stub->toSetProp_Native()->shape());
-        } else if (stub->isSetProp_Unboxed()) {
-            receiver = ReceiverGuard(stub->toSetProp_Unboxed()->group(), nullptr);
         } else {
             receivers.clear();
             return true;
         }
 
-        if (!AddReceiver(receiver, receivers, convertUnboxedGroups))
+        if (!AddReceiver(receiver, receivers))
             return false;
 
         stub = stub->next();
@@ -589,7 +538,7 @@ BaselineInspector::getTemplateObjectForNative(jsbytecode* pc, Native native)
 
 bool
 BaselineInspector::isOptimizableCallStringSplit(jsbytecode* pc, JSString** strOut, JSString** sepOut,
-                                                JSObject** objOut)
+                                                ArrayObject** objOut)
 {
     if (!hasBaselineScript())
         return false;
@@ -700,14 +649,12 @@ bool
 BaselineInspector::commonGetPropFunction(jsbytecode* pc, JSObject** holder, Shape** holderShape,
                                          JSFunction** commonGetter, Shape** globalShape,
                                          bool* isOwnProperty,
-                                         ReceiverVector& receivers,
-                                         ObjectGroupVector& convertUnboxedGroups)
+                                         ReceiverVector& receivers)
 {
     if (!hasBaselineScript())
         return false;
 
     MOZ_ASSERT(receivers.empty());
-    MOZ_ASSERT(convertUnboxedGroups.empty());
 
     *holder = nullptr;
     const ICEntry& entry = icEntryFromPC(pc);
@@ -719,7 +666,7 @@ BaselineInspector::commonGetPropFunction(jsbytecode* pc, JSObject** holder, Shap
         {
             ICGetPropCallGetter* nstub = static_cast<ICGetPropCallGetter*>(stub);
             bool isOwn = nstub->isOwnGetter();
-            if (!isOwn && !AddReceiver(nstub->receiverGuard(), receivers, convertUnboxedGroups))
+            if (!isOwn && !AddReceiver(nstub->receiverGuard(), receivers))
                 return false;
 
             if (!*holder) {
@@ -751,21 +698,19 @@ BaselineInspector::commonGetPropFunction(jsbytecode* pc, JSObject** holder, Shap
     if (!*holder)
         return false;
 
-    MOZ_ASSERT(*isOwnProperty == (receivers.empty() && convertUnboxedGroups.empty()));
+    MOZ_ASSERT(*isOwnProperty == (receivers.empty()));
     return true;
 }
 
 bool
 BaselineInspector::commonSetPropFunction(jsbytecode* pc, JSObject** holder, Shape** holderShape,
                                          JSFunction** commonSetter, bool* isOwnProperty,
-                                         ReceiverVector& receivers,
-                                         ObjectGroupVector& convertUnboxedGroups)
+                                         ReceiverVector& receivers)
 {
     if (!hasBaselineScript())
         return false;
 
     MOZ_ASSERT(receivers.empty());
-    MOZ_ASSERT(convertUnboxedGroups.empty());
 
     *holder = nullptr;
     const ICEntry& entry = icEntryFromPC(pc);
@@ -774,7 +719,7 @@ BaselineInspector::commonSetPropFunction(jsbytecode* pc, JSObject** holder, Shap
         if (stub->isSetProp_CallScripted() || stub->isSetProp_CallNative()) {
             ICSetPropCallSetter* nstub = static_cast<ICSetPropCallSetter*>(stub);
             bool isOwn = nstub->isOwnSetter();
-            if (!isOwn && !AddReceiver(nstub->receiverGuard(), receivers, convertUnboxedGroups))
+            if (!isOwn && !AddReceiver(nstub->receiverGuard(), receivers))
                 return false;
 
             if (!*holder) {
diff --git a/js/src/jit/BaselineInspector.h b/js/src/jit/BaselineInspector.h
index 961df18aa..1ed4b5547 100644
--- a/js/src/jit/BaselineInspector.h
+++ b/js/src/jit/BaselineInspector.h
@@ -95,8 +95,7 @@ class BaselineInspector
   public:
     typedef Vector<ReceiverGuard, 4, JitAllocPolicy> ReceiverVector;
     typedef Vector<ObjectGroup*, 4, JitAllocPolicy> ObjectGroupVector;
-    MOZ_MUST_USE bool maybeInfoForPropertyOp(jsbytecode* pc, ReceiverVector& receivers,
-                                             ObjectGroupVector& convertUnboxedGroups);
+    MOZ_MUST_USE bool maybeInfoForPropertyOp(jsbytecode* pc, ReceiverVector& receivers);
 
     SetElemICInspector setElemICInspector(jsbytecode* pc) {
         return makeICInspector<SetElemICInspector>(pc, ICStub::SetElem_Fallback);
@@ -114,7 +113,7 @@ class BaselineInspector
     bool hasSeenNonStringIterMore(jsbytecode* pc);
 
     MOZ_MUST_USE bool isOptimizableCallStringSplit(jsbytecode* pc, JSString** strOut,
-                                                   JSString** sepOut, JSObject** objOut);
+                                                   JSString** sepOut, ArrayObject** objOut);
     JSObject* getTemplateObject(jsbytecode* pc);
     JSObject* getTemplateObjectForNative(jsbytecode* pc, Native native);
     JSObject* getTemplateObjectForClassHook(jsbytecode* pc, const Class* clasp);
@@ -131,12 +130,10 @@ class BaselineInspector
 
     MOZ_MUST_USE bool commonGetPropFunction(jsbytecode* pc, JSObject** holder, Shape** holderShape,
                                             JSFunction** commonGetter, Shape** globalShape,
-                                            bool* isOwnProperty, ReceiverVector& receivers,
-                                            ObjectGroupVector& convertUnboxedGroups);
+                                            bool* isOwnProperty, ReceiverVector& receivers);
     MOZ_MUST_USE bool commonSetPropFunction(jsbytecode* pc, JSObject** holder, Shape** holderShape,
                                             JSFunction** commonSetter, bool* isOwnProperty,
-                                            ReceiverVector& receivers,
-                                            ObjectGroupVector& convertUnboxedGroups);
+                                            ReceiverVector& receivers);
 
     MOZ_MUST_USE bool instanceOfData(jsbytecode* pc, Shape** shape, uint32_t* slot,
                                      JSObject** prototypeObject);
diff --git a/js/src/jit/CacheIR.cpp b/js/src/jit/CacheIR.cpp
index f1061af70..d184ea40c 100644
--- a/js/src/jit/CacheIR.cpp
+++ b/js/src/jit/CacheIR.cpp
@@ -10,8 +10,7 @@
 #include "jit/IonCaches.h"
 
 #include "jsobjinlines.h"
-
-#include "vm/UnboxedObject-inl.h"
+#include "vm/NativeObject-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -60,10 +59,6 @@ GetPropIRGenerator::tryAttachStub(Maybe<CacheIRWriter>& writer)
             return false;
         if (!emitted_ && !tryAttachNative(*writer, obj, objId))
             return false;
-        if (!emitted_ && !tryAttachUnboxed(*writer, obj, objId))
-            return false;
-        if (!emitted_ && !tryAttachUnboxedExpando(*writer, obj, objId))
-            return false;
         if (!emitted_ && !tryAttachTypedObject(*writer, obj, objId))
             return false;
         if (!emitted_ && !tryAttachModuleNamespace(*writer, obj, objId))
@@ -163,19 +158,9 @@ GeneratePrototypeGuards(CacheIRWriter& writer, JSObject* obj, JSObject* holder,
 }
 
 static void
-TestMatchingReceiver(CacheIRWriter& writer, JSObject* obj, Shape* shape, ObjOperandId objId,
-                     Maybe<ObjOperandId>* expandoId)
+TestMatchingReceiver(CacheIRWriter& writer, JSObject* obj, Shape* shape, ObjOperandId objId)
 {
-    if (obj->is<UnboxedPlainObject>()) {
-        writer.guardGroup(objId, obj->group());
-
-        if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando()) {
-            expandoId->emplace(writer.guardAndLoadUnboxedExpando(objId));
-            writer.guardShape(expandoId->ref(), expando->lastProperty());
-        } else {
-            writer.guardNoUnboxedExpando(objId);
-        }
-    } else if (obj->is<UnboxedArrayObject>() || obj->is<TypedObject>()) {
+    if (obj->is<TypedObject>()) {
         writer.guardGroup(objId, obj->group());
     } else {
         Shape* shape = obj->maybeShape();
@@ -188,8 +173,7 @@ static void
 EmitReadSlotResult(CacheIRWriter& writer, JSObject* obj, JSObject* holder,
                    Shape* shape, ObjOperandId objId)
 {
-    Maybe<ObjOperandId> expandoId;
-    TestMatchingReceiver(writer, obj, shape, objId, &expandoId);
+    TestMatchingReceiver(writer, obj, shape, objId);
 
     ObjOperandId holderId;
     if (obj != holder) {
@@ -212,9 +196,6 @@ EmitReadSlotResult(CacheIRWriter& writer, JSObject* obj, JSObject* holder,
                 lastObjId = protoId;
             }
         }
-    } else if (obj->is<UnboxedPlainObject>()) {
-        holder = obj->as<UnboxedPlainObject>().maybeExpando();
-        holderId = *expandoId;
     } else {
         holderId = objId;
     }
@@ -266,51 +247,6 @@ GetPropIRGenerator::tryAttachNative(CacheIRWriter& writer, HandleObject obj, Obj
 }
 
 bool
-GetPropIRGenerator::tryAttachUnboxed(CacheIRWriter& writer, HandleObject obj, ObjOperandId objId)
-{
-    MOZ_ASSERT(!emitted_);
-
-    if (!obj->is<UnboxedPlainObject>())
-        return true;
-
-    const UnboxedLayout::Property* property = obj->as<UnboxedPlainObject>().layout().lookup(name_);
-    if (!property)
-        return true;
-
-    if (!cx_->runtime()->jitSupportsFloatingPoint)
-        return true;
-
-    writer.guardGroup(objId, obj->group());
-    writer.loadUnboxedPropertyResult(objId, property->type,
-                                     UnboxedPlainObject::offsetOfData() + property->offset);
-    emitted_ = true;
-    preliminaryObjectAction_ = PreliminaryObjectAction::Unlink;
-    return true;
-}
-
-bool
-GetPropIRGenerator::tryAttachUnboxedExpando(CacheIRWriter& writer, HandleObject obj, ObjOperandId objId)
-{
-    MOZ_ASSERT(!emitted_);
-
-    if (!obj->is<UnboxedPlainObject>())
-        return true;
-
-    UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando();
-    if (!expando)
-        return true;
-
-    Shape* shape = expando->lookup(cx_, NameToId(name_));
-    if (!shape || !shape->hasDefaultGetter() || !shape->hasSlot())
-        return true;
-
-    emitted_ = true;
-
-    EmitReadSlotResult(writer, obj, obj, shape, objId);
-    return true;
-}
-
-bool
 GetPropIRGenerator::tryAttachTypedObject(CacheIRWriter& writer, HandleObject obj, ObjOperandId objId)
 {
     MOZ_ASSERT(!emitted_);
@@ -368,13 +304,6 @@ GetPropIRGenerator::tryAttachObjectLength(CacheIRWriter& writer, HandleObject ob
         return true;
     }
 
-    if (obj->is<UnboxedArrayObject>()) {
-        writer.guardClass(objId, GuardClassKind::UnboxedArray);
-        writer.loadUnboxedArrayLengthResult(objId);
-        emitted_ = true;
-        return true;
-    }
-
     if (obj->is<ArgumentsObject>() && !obj->as<ArgumentsObject>().hasOverriddenLength()) {
         if (obj->is<MappedArgumentsObject>()) {
             writer.guardClass(objId, GuardClassKind::MappedArguments);
diff --git a/js/src/jit/CacheIR.h b/js/src/jit/CacheIR.h
index 51e55f48b..ae55cfebb 100644
--- a/js/src/jit/CacheIR.h
+++ b/js/src/jit/CacheIR.h
@@ -87,16 +87,12 @@ class ObjOperandId : public OperandId
     _(GuardClass)                         \
     _(GuardSpecificObject)                \
     _(GuardNoDetachedTypedObjects)        \
-    _(GuardNoUnboxedExpando)              \
-    _(GuardAndLoadUnboxedExpando)         \
     _(LoadObject)                         \
     _(LoadProto)                          \
     _(LoadFixedSlotResult)                \
     _(LoadDynamicSlotResult)              \
-    _(LoadUnboxedPropertyResult)          \
     _(LoadTypedObjectResult)              \
     _(LoadInt32ArrayLengthResult)         \
-    _(LoadUnboxedArrayLengthResult)       \
     _(LoadArgumentsObjectLengthResult)    \
     _(LoadUndefinedResult)
 
@@ -128,7 +124,6 @@ struct StubField {
 enum class GuardClassKind
 {
     Array,
-    UnboxedArray,
     MappedArguments,
     UnmappedArguments,
 };
@@ -276,15 +271,6 @@ class MOZ_RAII CacheIRWriter
     void guardNoDetachedTypedObjects() {
         writeOp(CacheOp::GuardNoDetachedTypedObjects);
     }
-    void guardNoUnboxedExpando(ObjOperandId obj) {
-        writeOpWithOperandId(CacheOp::GuardNoUnboxedExpando, obj);
-    }
-    ObjOperandId guardAndLoadUnboxedExpando(ObjOperandId obj) {
-        ObjOperandId res(nextOperandId_++);
-        writeOpWithOperandId(CacheOp::GuardAndLoadUnboxedExpando, obj);
-        writeOperandId(res);
-        return res;
-    }
 
     ObjOperandId loadObject(JSObject* obj) {
         ObjOperandId res(nextOperandId_++);
@@ -310,11 +296,6 @@ class MOZ_RAII CacheIRWriter
         writeOpWithOperandId(CacheOp::LoadDynamicSlotResult, obj);
         addStubWord(offset, StubField::GCType::NoGCThing);
     }
-    void loadUnboxedPropertyResult(ObjOperandId obj, JSValueType type, size_t offset) {
-        writeOpWithOperandId(CacheOp::LoadUnboxedPropertyResult, obj);
-        buffer_.writeByte(uint32_t(type));
-        addStubWord(offset, StubField::GCType::NoGCThing);
-    }
     void loadTypedObjectResult(ObjOperandId obj, uint32_t offset, TypedThingLayout layout,
                                uint32_t typeDescr) {
         MOZ_ASSERT(uint32_t(layout) <= UINT8_MAX);
@@ -327,9 +308,6 @@ class MOZ_RAII CacheIRWriter
     void loadInt32ArrayLengthResult(ObjOperandId obj) {
         writeOpWithOperandId(CacheOp::LoadInt32ArrayLengthResult, obj);
     }
-    void loadUnboxedArrayLengthResult(ObjOperandId obj) {
-        writeOpWithOperandId(CacheOp::LoadUnboxedArrayLengthResult, obj);
-    }
     void loadArgumentsObjectLengthResult(ObjOperandId obj) {
         writeOpWithOperandId(CacheOp::LoadArgumentsObjectLengthResult, obj);
     }
@@ -411,9 +389,6 @@ class MOZ_RAII GetPropIRGenerator
     PreliminaryObjectAction preliminaryObjectAction_;
 
     MOZ_MUST_USE bool tryAttachNative(CacheIRWriter& writer, HandleObject obj, ObjOperandId objId);
-    MOZ_MUST_USE bool tryAttachUnboxed(CacheIRWriter& writer, HandleObject obj, ObjOperandId objId);
-    MOZ_MUST_USE bool tryAttachUnboxedExpando(CacheIRWriter& writer, HandleObject obj,
-                                              ObjOperandId objId);
     MOZ_MUST_USE bool tryAttachTypedObject(CacheIRWriter& writer, HandleObject obj,
                                            ObjOperandId objId);
     MOZ_MUST_USE bool tryAttachObjectLength(CacheIRWriter& writer, HandleObject obj,
diff --git a/js/src/jit/CodeGenerator.cpp b/js/src/jit/CodeGenerator.cpp
index 16d026092..fcb711237 100644
--- a/js/src/jit/CodeGenerator.cpp
+++ b/js/src/jit/CodeGenerator.cpp
@@ -25,6 +25,7 @@
 #include "builtin/Eval.h"
 #include "builtin/TypedObject.h"
 #include "gc/Nursery.h"
+#include "gc/StoreBuffer-inl.h"
 #include "irregexp/NativeRegExpMacroAssembler.h"
 #include "jit/AtomicOperations.h"
 #include "jit/BaselineCompiler.h"
@@ -3027,19 +3028,10 @@ CodeGenerator::visitStoreSlotV(LStoreSlotV* lir)
 
 static void
 GuardReceiver(MacroAssembler& masm, const ReceiverGuard& guard,
-              Register obj, Register scratch, Label* miss, bool checkNullExpando)
+              Register obj, Register scratch, Label* miss)
 {
     if (guard.group) {
         masm.branchTestObjGroup(Assembler::NotEqual, obj, guard.group, miss);
-
-        Address expandoAddress(obj, UnboxedPlainObject::offsetOfExpando());
-        if (guard.shape) {
-            masm.loadPtr(expandoAddress, scratch);
-            masm.branchPtr(Assembler::Equal, scratch, ImmWord(0), miss);
-            masm.branchTestObjShape(Assembler::NotEqual, scratch, guard.shape, miss);
-        } else if (checkNullExpando) {
-            masm.branchPtr(Assembler::NotEqual, expandoAddress, ImmWord(0), miss);
-        }
     } else {
         masm.branchTestObjShape(Assembler::NotEqual, obj, guard.shape, miss);
     }
@@ -3058,13 +3050,11 @@ CodeGenerator::emitGetPropertyPolymorphic(LInstruction* ins, Register obj, Regis
 
         Label next;
         masm.comment("GuardReceiver");
-        GuardReceiver(masm, receiver, obj, scratch, &next, /* checkNullExpando = */ false);
+        GuardReceiver(masm, receiver, obj, scratch, &next);
 
         if (receiver.shape) {
             masm.comment("loadTypedOrValue");
-            // If this is an unboxed expando access, GuardReceiver loaded the
-            // expando object into scratch.
-            Register target = receiver.group ? scratch : obj;
+            Register target = obj;
 
             Shape* shape = mir->shape(i);
             if (shape->slot() < shape->numFixedSlots()) {
@@ -3077,13 +3067,6 @@ CodeGenerator::emitGetPropertyPolymorphic(LInstruction* ins, Register obj, Regis
                 masm.loadPtr(Address(target, NativeObject::offsetOfSlots()), scratch);
                 masm.loadTypedOrValue(Address(scratch, offset), output);
             }
-        } else {
-            masm.comment("loadUnboxedProperty");
-            const UnboxedLayout::Property* property =
-                receiver.group->unboxedLayout().lookup(mir->name());
-            Address propertyAddr(obj, UnboxedPlainObject::offsetOfData() + property->offset);
-
-            masm.loadUnboxedProperty(propertyAddr, property->type, output);
         }
 
         if (i == mir->numReceivers() - 1) {
@@ -3124,8 +3107,6 @@ EmitUnboxedPreBarrier(MacroAssembler &masm, T address, JSValueType type)
         masm.patchableCallPreBarrier(address, MIRType::Object);
     else if (type == JSVAL_TYPE_STRING)
         masm.patchableCallPreBarrier(address, MIRType::String);
-    else
-        MOZ_ASSERT(!UnboxedTypeNeedsPreBarrier(type));
 }
 
 void
@@ -3139,12 +3120,10 @@ CodeGenerator::emitSetPropertyPolymorphic(LInstruction* ins, Register obj, Regis
         ReceiverGuard receiver = mir->receiver(i);
 
         Label next;
-        GuardReceiver(masm, receiver, obj, scratch, &next, /* checkNullExpando = */ false);
+        GuardReceiver(masm, receiver, obj, scratch, &next);
 
         if (receiver.shape) {
-            // If this is an unboxed expando access, GuardReceiver loaded the
-            // expando object into scratch.
-            Register target = receiver.group ? scratch : obj;
+            Register target = obj;
 
             Shape* shape = mir->shape(i);
             if (shape->slot() < shape->numFixedSlots()) {
@@ -3161,13 +3140,6 @@ CodeGenerator::emitSetPropertyPolymorphic(LInstruction* ins, Register obj, Regis
                     emitPreBarrier(addr);
                 masm.storeConstantOrRegister(value, addr);
             }
-        } else {
-            const UnboxedLayout::Property* property =
-                receiver.group->unboxedLayout().lookup(mir->name());
-            Address propertyAddr(obj, UnboxedPlainObject::offsetOfData() + property->offset);
-
-            EmitUnboxedPreBarrier(masm, propertyAddr, property->type);
-            masm.storeUnboxedProperty(propertyAddr, property->type, value, nullptr);
         }
 
         if (i == mir->numReceivers() - 1) {
@@ -3208,9 +3180,7 @@ CodeGenerator::visitSetPropertyPolymorphicT(LSetPropertyPolymorphicT* ins)
 void
 CodeGenerator::visitElements(LElements* lir)
 {
-    Address elements(ToRegister(lir->object()),
-                     lir->mir()->unboxed() ? UnboxedArrayObject::offsetOfElements()
-                                           : NativeObject::offsetOfElements());
+    Address elements(ToRegister(lir->object()), NativeObject::offsetOfElements());
     masm.loadPtr(elements, ToRegister(lir->output()));
 }
 
@@ -3319,7 +3289,7 @@ CodeGenerator::visitGuardReceiverPolymorphic(LGuardReceiverPolymorphic* lir)
         const ReceiverGuard& receiver = mir->receiver(i);
 
         Label next;
-        GuardReceiver(masm, receiver, obj, temp, &next, /* checkNullExpando = */ true);
+        GuardReceiver(masm, receiver, obj, temp, &next);
 
         if (i == mir->numReceivers() - 1) {
             bailoutFrom(&next, lir->snapshot());
@@ -3333,27 +3303,6 @@ CodeGenerator::visitGuardReceiverPolymorphic(LGuardReceiverPolymorphic* lir)
 }
 
 void
-CodeGenerator::visitGuardUnboxedExpando(LGuardUnboxedExpando* lir)
-{
-    Label miss;
-
-    Register obj = ToRegister(lir->object());
-    masm.branchPtr(lir->mir()->requireExpando() ? Assembler::Equal : Assembler::NotEqual,
-                   Address(obj, UnboxedPlainObject::offsetOfExpando()), ImmWord(0), &miss);
-
-    bailoutFrom(&miss, lir->snapshot());
-}
-
-void
-CodeGenerator::visitLoadUnboxedExpando(LLoadUnboxedExpando* lir)
-{
-    Register obj = ToRegister(lir->object());
-    Register result = ToRegister(lir->getDef(0));
-
-    masm.loadPtr(Address(obj, UnboxedPlainObject::offsetOfExpando()), result);
-}
-
-void
 CodeGenerator::visitTypeBarrierV(LTypeBarrierV* lir)
 {
     ValueOperand operand = ToValue(lir, LTypeBarrierV::Input);
@@ -5217,11 +5166,11 @@ static JSObject*
 NewArrayWithGroup(JSContext* cx, uint32_t length, HandleObjectGroup group,
                   bool convertDoubleElements)
 {
-    JSObject* res = NewFullyAllocatedArrayTryUseGroup(cx, group, length);
+    ArrayObject* res = NewFullyAllocatedArrayTryUseGroup(cx, group, length);
     if (!res)
         return nullptr;
     if (convertDoubleElements)
-        res->as<ArrayObject>().setShouldConvertDoubleElements();
+        res->setShouldConvertDoubleElements();
     return res;
 }
 
@@ -5367,7 +5316,7 @@ CodeGenerator::visitNewArrayCopyOnWrite(LNewArrayCopyOnWrite* lir)
     masm.bind(ool->rejoin());
 }
 
-typedef JSObject* (*ArrayConstructorOneArgFn)(JSContext*, HandleObjectGroup, int32_t length);
+typedef ArrayObject* (*ArrayConstructorOneArgFn)(JSContext*, HandleObjectGroup, int32_t length);
 static const VMFunction ArrayConstructorOneArgInfo =
     FunctionInfo<ArrayConstructorOneArgFn>(ArrayConstructorOneArg, "ArrayConstructorOneArg");
 
@@ -5387,21 +5336,11 @@ CodeGenerator::visitNewArrayDynamicLength(LNewArrayDynamicLength* lir)
 
     bool canInline = true;
     size_t inlineLength = 0;
-    if (templateObject->is<ArrayObject>()) {
-        if (templateObject->as<ArrayObject>().hasFixedElements()) {
-            size_t numSlots = gc::GetGCKindSlots(templateObject->asTenured().getAllocKind());
-            inlineLength = numSlots - ObjectElements::VALUES_PER_HEADER;
-        } else {
-            canInline = false;
-        }
+    if (templateObject->as<ArrayObject>().hasFixedElements()) {
+        size_t numSlots = gc::GetGCKindSlots(templateObject->asTenured().getAllocKind());
+        inlineLength = numSlots - ObjectElements::VALUES_PER_HEADER;
     } else {
-        if (templateObject->as<UnboxedArrayObject>().hasInlineElements()) {
-            size_t nbytes =
-                templateObject->tenuredSizeOfThis() - UnboxedArrayObject::offsetOfInlineElements();
-            inlineLength = nbytes / templateObject->as<UnboxedArrayObject>().elementSize();
-        } else {
-            canInline = false;
-        }
+        canInline = false;
     }
 
     if (canInline) {
@@ -7823,7 +7762,7 @@ CodeGenerator::visitSinCos(LSinCos *lir)
     masm.freeStack(sizeof(double) * 2);
 }
 
-typedef JSObject* (*StringSplitFn)(JSContext*, HandleObjectGroup, HandleString, HandleString, uint32_t);
+typedef ArrayObject* (*StringSplitFn)(JSContext*, HandleObjectGroup, HandleString, HandleString, uint32_t);
 static const VMFunction StringSplitInfo =
     FunctionInfo<StringSplitFn>(js::str_split_string, "str_split_string");
 
@@ -7858,49 +7797,6 @@ CodeGenerator::visitSetInitializedLength(LSetInitializedLength* lir)
 }
 
 void
-CodeGenerator::visitUnboxedArrayLength(LUnboxedArrayLength* lir)
-{
-    Register obj = ToRegister(lir->object());
-    Register result = ToRegister(lir->output());
-    masm.load32(Address(obj, UnboxedArrayObject::offsetOfLength()), result);
-}
-
-void
-CodeGenerator::visitUnboxedArrayInitializedLength(LUnboxedArrayInitializedLength* lir)
-{
-    Register obj = ToRegister(lir->object());
-    Register result = ToRegister(lir->output());
-    masm.load32(Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()), result);
-    masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), result);
-}
-
-void
-CodeGenerator::visitIncrementUnboxedArrayInitializedLength(LIncrementUnboxedArrayInitializedLength* lir)
-{
-    Register obj = ToRegister(lir->object());
-    masm.add32(Imm32(1), Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()));
-}
-
-void
-CodeGenerator::visitSetUnboxedArrayInitializedLength(LSetUnboxedArrayInitializedLength* lir)
-{
-    Register obj = ToRegister(lir->object());
-    RegisterOrInt32Constant key = ToRegisterOrInt32Constant(lir->length());
-    Register temp = ToRegister(lir->temp());
-
-    Address initLengthAddr(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-    masm.load32(initLengthAddr, temp);
-    masm.and32(Imm32(UnboxedArrayObject::CapacityMask), temp);
-
-    if (key.isRegister())
-        masm.or32(key.reg(), temp);
-    else
-        masm.or32(Imm32(key.constant()), temp);
-
-    masm.store32(temp, initLengthAddr);
-}
-
-void
 CodeGenerator::visitNotO(LNotO* lir)
 {
     MOZ_ASSERT(lir->mir()->operandMightEmulateUndefined(),
@@ -8196,46 +8092,19 @@ CodeGenerator::emitStoreElementHoleT(T* lir)
     OutOfLineStoreElementHole* ool = new(alloc()) OutOfLineStoreElementHole(lir);
     addOutOfLineCode(ool, lir->mir());
 
-    Register obj = ToRegister(lir->object());
     Register elements = ToRegister(lir->elements());
     const LAllocation* index = lir->index();
     RegisterOrInt32Constant key = ToRegisterOrInt32Constant(index);
 
-    JSValueType unboxedType = lir->mir()->unboxedType();
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        Address initLength(elements, ObjectElements::offsetOfInitializedLength());
-        masm.branch32(Assembler::BelowOrEqual, initLength, key, ool->entry());
+    Address initLength(elements, ObjectElements::offsetOfInitializedLength());
+    masm.branch32(Assembler::BelowOrEqual, initLength, key, ool->entry());
 
-        if (lir->mir()->needsBarrier())
-            emitPreBarrier(elements, index, 0);
-
-        masm.bind(ool->rejoinStore());
-        emitStoreElementTyped(lir->value(), lir->mir()->value()->type(), lir->mir()->elementType(),
-                              elements, index, 0);
-    } else {
-        Register temp = ToRegister(lir->getTemp(0));
-        Address initLength(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-        masm.load32(initLength, temp);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), temp);
-        masm.branch32(Assembler::BelowOrEqual, temp, key, ool->entry());
-
-        ConstantOrRegister v = ToConstantOrRegister(lir->value(), lir->mir()->value()->type());
-
-        if (index->isConstant()) {
-            Address address(elements, ToInt32(index) * UnboxedTypeSize(unboxedType));
-            EmitUnboxedPreBarrier(masm, address, unboxedType);
-
-            masm.bind(ool->rejoinStore());
-            masm.storeUnboxedProperty(address, unboxedType, v, nullptr);
-        } else {
-            BaseIndex address(elements, ToRegister(index),
-                              ScaleFromElemWidth(UnboxedTypeSize(unboxedType)));
-            EmitUnboxedPreBarrier(masm, address, unboxedType);
+    if (lir->mir()->needsBarrier())
+        emitPreBarrier(elements, index, 0);
 
-            masm.bind(ool->rejoinStore());
-            masm.storeUnboxedProperty(address, unboxedType, v, nullptr);
-        }
-    }
+    masm.bind(ool->rejoinStore());
+    emitStoreElementTyped(lir->value(), lir->mir()->value()->type(), lir->mir()->elementType(),
+                          elements, index, 0);
 
     masm.bind(ool->rejoin());
 }
@@ -8255,47 +8124,22 @@ CodeGenerator::emitStoreElementHoleV(T* lir)
     OutOfLineStoreElementHole* ool = new(alloc()) OutOfLineStoreElementHole(lir);
     addOutOfLineCode(ool, lir->mir());
 
-    Register obj = ToRegister(lir->object());
     Register elements = ToRegister(lir->elements());
     const LAllocation* index = lir->index();
     const ValueOperand value = ToValue(lir, T::Value);
     RegisterOrInt32Constant key = ToRegisterOrInt32Constant(index);
 
-    JSValueType unboxedType = lir->mir()->unboxedType();
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        Address initLength(elements, ObjectElements::offsetOfInitializedLength());
-        masm.branch32(Assembler::BelowOrEqual, initLength, key, ool->entry());
-
-        if (lir->mir()->needsBarrier())
-            emitPreBarrier(elements, index, 0);
+    Address initLength(elements, ObjectElements::offsetOfInitializedLength());
+    masm.branch32(Assembler::BelowOrEqual, initLength, key, ool->entry());
 
-        masm.bind(ool->rejoinStore());
-        if (index->isConstant())
-            masm.storeValue(value, Address(elements, ToInt32(index) * sizeof(js::Value)));
-        else
-            masm.storeValue(value, BaseIndex(elements, ToRegister(index), TimesEight));
-    } else {
-        Register temp = ToRegister(lir->getTemp(0));
-        Address initLength(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-        masm.load32(initLength, temp);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), temp);
-        masm.branch32(Assembler::BelowOrEqual, temp, key, ool->entry());
-
-        if (index->isConstant()) {
-            Address address(elements, ToInt32(index) * UnboxedTypeSize(unboxedType));
-            EmitUnboxedPreBarrier(masm, address, unboxedType);
-
-            masm.bind(ool->rejoinStore());
-            masm.storeUnboxedProperty(address, unboxedType, ConstantOrRegister(value), nullptr);
-        } else {
-            BaseIndex address(elements, ToRegister(index),
-                              ScaleFromElemWidth(UnboxedTypeSize(unboxedType)));
-            EmitUnboxedPreBarrier(masm, address, unboxedType);
+    if (lir->mir()->needsBarrier())
+        emitPreBarrier(elements, index, 0);
 
-            masm.bind(ool->rejoinStore());
-            masm.storeUnboxedProperty(address, unboxedType, ConstantOrRegister(value), nullptr);
-        }
-    }
+    masm.bind(ool->rejoinStore());
+    if (index->isConstant())
+        masm.storeValue(value, Address(elements, ToInt32(index) * sizeof(js::Value)));
+    else
+        masm.storeValue(value, BaseIndex(elements, ToRegister(index), TimesEight));
 
     masm.bind(ool->rejoin());
 }
@@ -8366,11 +8210,10 @@ CodeGenerator::visitFallibleStoreElementV(LFallibleStoreElementV* lir)
     masm.bind(&isFrozen);
 }
 
-typedef bool (*SetDenseOrUnboxedArrayElementFn)(JSContext*, HandleObject, int32_t,
-                                                HandleValue, bool strict);
-static const VMFunction SetDenseOrUnboxedArrayElementInfo =
-    FunctionInfo<SetDenseOrUnboxedArrayElementFn>(SetDenseOrUnboxedArrayElement,
-                                                  "SetDenseOrUnboxedArrayElement");
+typedef bool (*SetDenseElementFn)(JSContext*, HandleNativeObject, int32_t, HandleValue,
+                                  bool strict);
+static const VMFunction SetDenseElementInfo =
+    FunctionInfo<SetDenseElementFn>(jit::SetDenseElement, "SetDenseElement");
 
 void
 CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
@@ -8380,8 +8223,6 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
     const LAllocation* index;
     MIRType valueType;
     ConstantOrRegister value;
-    JSValueType unboxedType;
-    LDefinition *temp = nullptr;
 
     if (ins->isStoreElementHoleV()) {
         LStoreElementHoleV* store = ins->toStoreElementHoleV();
@@ -8390,8 +8231,6 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
         index = store->index();
         valueType = store->mir()->value()->type();
         value = TypedOrValueRegister(ToValue(store, LStoreElementHoleV::Value));
-        unboxedType = store->mir()->unboxedType();
-        temp = store->getTemp(0);
     } else if (ins->isFallibleStoreElementV()) {
         LFallibleStoreElementV* store = ins->toFallibleStoreElementV();
         object = ToRegister(store->object());
@@ -8399,8 +8238,6 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
         index = store->index();
         valueType = store->mir()->value()->type();
         value = TypedOrValueRegister(ToValue(store, LFallibleStoreElementV::Value));
-        unboxedType = store->mir()->unboxedType();
-        temp = store->getTemp(0);
     } else if (ins->isStoreElementHoleT()) {
         LStoreElementHoleT* store = ins->toStoreElementHoleT();
         object = ToRegister(store->object());
@@ -8411,8 +8248,6 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
             value = ConstantOrRegister(store->value()->toConstant()->toJSValue());
         else
             value = TypedOrValueRegister(valueType, ToAnyRegister(store->value()));
-        unboxedType = store->mir()->unboxedType();
-        temp = store->getTemp(0);
     } else { // ins->isFallibleStoreElementT()
         LFallibleStoreElementT* store = ins->toFallibleStoreElementT();
         object = ToRegister(store->object());
@@ -8423,8 +8258,6 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
             value = ConstantOrRegister(store->value()->toConstant()->toJSValue());
         else
             value = TypedOrValueRegister(valueType, ToAnyRegister(store->value()));
-        unboxedType = store->mir()->unboxedType();
-        temp = store->getTemp(0);
     }
 
     RegisterOrInt32Constant key = ToRegisterOrInt32Constant(index);
@@ -8435,54 +8268,32 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
     Label callStub;
 #if defined(JS_CODEGEN_MIPS32) || defined(JS_CODEGEN_MIPS64)
     // Had to reimplement for MIPS because there are no flags.
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        Address initLength(elements, ObjectElements::offsetOfInitializedLength());
-        masm.branch32(Assembler::NotEqual, initLength, key, &callStub);
-    } else {
-        Address initLength(object, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-        masm.load32(initLength, ToRegister(temp));
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), ToRegister(temp));
-        masm.branch32(Assembler::NotEqual, ToRegister(temp), key, &callStub);
-    }
+    Address initLength(elements, ObjectElements::offsetOfInitializedLength());
+    masm.branch32(Assembler::NotEqual, initLength, key, &callStub);
 #else
     masm.j(Assembler::NotEqual, &callStub);
 #endif
 
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        // Check array capacity.
-        masm.branch32(Assembler::BelowOrEqual, Address(elements, ObjectElements::offsetOfCapacity()),
-                      key, &callStub);
+    // Check array capacity.
+    masm.branch32(Assembler::BelowOrEqual, Address(elements, ObjectElements::offsetOfCapacity()),
+                  key, &callStub);
 
-        // Update initialized length. The capacity guard above ensures this won't overflow,
-        // due to MAX_DENSE_ELEMENTS_COUNT.
-        masm.inc32(&key);
-        masm.store32(key, Address(elements, ObjectElements::offsetOfInitializedLength()));
-
-        // Update length if length < initializedLength.
-        Label dontUpdate;
-        masm.branch32(Assembler::AboveOrEqual, Address(elements, ObjectElements::offsetOfLength()),
-                      key, &dontUpdate);
-        masm.store32(key, Address(elements, ObjectElements::offsetOfLength()));
-        masm.bind(&dontUpdate);
-
-        masm.dec32(&key);
-    } else {
-        // Check array capacity.
-        masm.checkUnboxedArrayCapacity(object, key, ToRegister(temp), &callStub);
+    // Update initialized length. The capacity guard above ensures this won't overflow,
+    // due to MAX_DENSE_ELEMENTS_COUNT.
+    masm.inc32(&key);
+    masm.store32(key, Address(elements, ObjectElements::offsetOfInitializedLength()));
 
-        // Update initialized length.
-        masm.add32(Imm32(1), Address(object, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()));
+    // Update length if length < initializedLength.
+    Label dontUpdate;
+    masm.branch32(Assembler::AboveOrEqual, Address(elements, ObjectElements::offsetOfLength()),
+                  key, &dontUpdate);
+    masm.store32(key, Address(elements, ObjectElements::offsetOfLength()));
+    masm.bind(&dontUpdate);
 
-        // Update length if length < initializedLength.
-        Address lengthAddr(object, UnboxedArrayObject::offsetOfLength());
-        Label dontUpdate;
-        masm.branch32(Assembler::Above, lengthAddr, key, &dontUpdate);
-        masm.add32(Imm32(1), lengthAddr);
-        masm.bind(&dontUpdate);
-    }
+    masm.dec32(&key);
 
     if ((ins->isStoreElementHoleT() || ins->isFallibleStoreElementT()) &&
-        unboxedType == JSVAL_TYPE_MAGIC && valueType != MIRType::Double)
+        valueType != MIRType::Double)
     {
         // The inline path for StoreElementHoleT and FallibleStoreElementT does not always store
         // the type tag, so we do the store on the OOL path. We use MIRType::None for the element
@@ -8511,7 +8322,7 @@ CodeGenerator::visitOutOfLineStoreElementHole(OutOfLineStoreElementHole* ool)
     else
         pushArg(ToRegister(index));
     pushArg(object);
-    callVM(SetDenseOrUnboxedArrayElementInfo, ins);
+    callVM(SetDenseElementInfo, ins);
 
     restoreLive(ins);
     masm.jump(ool->rejoin());
@@ -8568,29 +8379,6 @@ CodeGenerator::visitStoreUnboxedPointer(LStoreUnboxedPointer* lir)
     }
 }
 
-typedef bool (*ConvertUnboxedObjectToNativeFn)(JSContext*, JSObject*);
-static const VMFunction ConvertUnboxedPlainObjectToNativeInfo =
-    FunctionInfo<ConvertUnboxedObjectToNativeFn>(UnboxedPlainObject::convertToNative,
-                                                 "UnboxedPlainObject::convertToNative");
-static const VMFunction ConvertUnboxedArrayObjectToNativeInfo =
-    FunctionInfo<ConvertUnboxedObjectToNativeFn>(UnboxedArrayObject::convertToNative,
-                                                 "UnboxedArrayObject::convertToNative");
-
-void
-CodeGenerator::visitConvertUnboxedObjectToNative(LConvertUnboxedObjectToNative* lir)
-{
-    Register object = ToRegister(lir->getOperand(0));
-
-    OutOfLineCode* ool = oolCallVM(lir->mir()->group()->unboxedLayoutDontCheckGeneration().isArray()
-                                   ? ConvertUnboxedArrayObjectToNativeInfo
-                                   : ConvertUnboxedPlainObjectToNativeInfo,
-                                   lir, ArgList(object), StoreNothing());
-
-    masm.branchPtr(Assembler::Equal, Address(object, JSObject::offsetOfGroup()),
-                   ImmGCPtr(lir->mir()->group()), ool->entry());
-    masm.bind(ool->rejoin());
-}
-
 typedef bool (*ArrayPopShiftFn)(JSContext*, HandleObject, MutableHandleValue);
 static const VMFunction ArrayPopDenseInfo =
     FunctionInfo<ArrayPopShiftFn>(jit::ArrayPopDense, "ArrayPopDense");
@@ -8615,20 +8403,11 @@ CodeGenerator::emitArrayPopShift(LInstruction* lir, const MArrayPopShift* mir, R
 
     // Load elements and length, and VM call if length != initializedLength.
     RegisterOrInt32Constant key = RegisterOrInt32Constant(lengthTemp);
-    if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
-        masm.loadPtr(Address(obj, NativeObject::offsetOfElements()), elementsTemp);
-        masm.load32(Address(elementsTemp, ObjectElements::offsetOfLength()), lengthTemp);
+    masm.loadPtr(Address(obj, NativeObject::offsetOfElements()), elementsTemp);
+    masm.load32(Address(elementsTemp, ObjectElements::offsetOfLength()), lengthTemp);
 
-        Address initLength(elementsTemp, ObjectElements::offsetOfInitializedLength());
-        masm.branch32(Assembler::NotEqual, initLength, key, ool->entry());
-    } else {
-        masm.loadPtr(Address(obj, UnboxedArrayObject::offsetOfElements()), elementsTemp);
-        masm.load32(Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()), lengthTemp);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), lengthTemp);
-
-        Address lengthAddr(obj, UnboxedArrayObject::offsetOfLength());
-        masm.branch32(Assembler::NotEqual, lengthAddr, key, ool->entry());
-    }
+    Address initLength(elementsTemp, ObjectElements::offsetOfInitializedLength());
+    masm.branch32(Assembler::NotEqual, initLength, key, ool->entry());
 
     // Test for length != 0. On zero length either take a VM call or generate
     // an undefined value, depending on whether the call is known to produce
@@ -8640,13 +8419,10 @@ CodeGenerator::emitArrayPopShift(LInstruction* lir, const MArrayPopShift* mir, R
 
         // According to the spec we need to set the length 0 (which is already 0).
         // This is observable when the array length is made non-writable.
-        // Handle this case in the OOL. When freezing an unboxed array it is converted
-        // to an normal array.
-        if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
-            Address elementFlags(elementsTemp, ObjectElements::offsetOfFlags());
-            Imm32 bit(ObjectElements::NONWRITABLE_ARRAY_LENGTH);
-            masm.branchTest32(Assembler::NonZero, elementFlags, bit, ool->entry());
-        }
+        // Handle this case in the OOL.
+        Address elementFlags(elementsTemp, ObjectElements::offsetOfFlags());
+        Imm32 bit(ObjectElements::NONWRITABLE_ARRAY_LENGTH);
+        masm.branchTest32(Assembler::NonZero, elementFlags, bit, ool->entry());
 
         masm.moveValue(UndefinedValue(), out.valueReg());
         masm.jump(&done);
@@ -8658,41 +8434,25 @@ CodeGenerator::emitArrayPopShift(LInstruction* lir, const MArrayPopShift* mir, R
     masm.dec32(&key);
 
     if (mir->mode() == MArrayPopShift::Pop) {
-        if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
-            BaseIndex addr(elementsTemp, lengthTemp, TimesEight);
-            masm.loadElementTypedOrValue(addr, out, mir->needsHoleCheck(), ool->entry());
-        } else {
-            size_t elemSize = UnboxedTypeSize(mir->unboxedType());
-            BaseIndex addr(elementsTemp, lengthTemp, ScaleFromElemWidth(elemSize));
-            masm.loadUnboxedProperty(addr, mir->unboxedType(), out);
-        }
+        BaseIndex addr(elementsTemp, lengthTemp, TimesEight);
+        masm.loadElementTypedOrValue(addr, out, mir->needsHoleCheck(), ool->entry());
     } else {
         MOZ_ASSERT(mir->mode() == MArrayPopShift::Shift);
         Address addr(elementsTemp, 0);
-        if (mir->unboxedType() == JSVAL_TYPE_MAGIC)
-            masm.loadElementTypedOrValue(addr, out, mir->needsHoleCheck(), ool->entry());
-        else
-            masm.loadUnboxedProperty(addr, mir->unboxedType(), out);
+        masm.loadElementTypedOrValue(addr, out, mir->needsHoleCheck(), ool->entry());
     }
 
-    if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
-        // Handle the failure case when the array length is non-writable in the
-        // OOL path.  (Unlike in the adding-an-element cases, we can't rely on the
-        // capacity <= length invariant for such arrays to avoid an explicit
-        // check.)
-        Address elementFlags(elementsTemp, ObjectElements::offsetOfFlags());
-        Imm32 bit(ObjectElements::NONWRITABLE_ARRAY_LENGTH);
-        masm.branchTest32(Assembler::NonZero, elementFlags, bit, ool->entry());
+    // Handle the failure case when the array length is non-writable in the
+    // OOL path.  (Unlike in the adding-an-element cases, we can't rely on the
+    // capacity <= length invariant for such arrays to avoid an explicit
+    // check.)
+    Address elementFlags(elementsTemp, ObjectElements::offsetOfFlags());
+    Imm32 bit(ObjectElements::NONWRITABLE_ARRAY_LENGTH);
+    masm.branchTest32(Assembler::NonZero, elementFlags, bit, ool->entry());
 
-        // Now adjust length and initializedLength.
-        masm.store32(lengthTemp, Address(elementsTemp, ObjectElements::offsetOfLength()));
-        masm.store32(lengthTemp, Address(elementsTemp, ObjectElements::offsetOfInitializedLength()));
-    } else {
-        // Unboxed arrays always have writable lengths. Adjust length and
-        // initializedLength.
-        masm.store32(lengthTemp, Address(obj, UnboxedArrayObject::offsetOfLength()));
-        masm.add32(Imm32(-1), Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()));
-    }
+    // Now adjust length and initializedLength.
+    masm.store32(lengthTemp, Address(elementsTemp, ObjectElements::offsetOfLength()));
+    masm.store32(lengthTemp, Address(elementsTemp, ObjectElements::offsetOfInitializedLength()));
 
     if (mir->mode() == MArrayPopShift::Shift) {
         // Don't save the temp registers.
@@ -8731,7 +8491,7 @@ CodeGenerator::visitArrayPopShiftT(LArrayPopShiftT* lir)
     emitArrayPopShift(lir, lir->mir(), obj, elements, length, out);
 }
 
-typedef bool (*ArrayPushDenseFn)(JSContext*, HandleObject, HandleValue, uint32_t*);
+typedef bool (*ArrayPushDenseFn)(JSContext*, HandleArrayObject, HandleValue, uint32_t*);
 static const VMFunction ArrayPushDenseInfo =
     FunctionInfo<ArrayPushDenseFn>(jit::ArrayPushDense, "ArrayPushDense");
 
@@ -8742,50 +8502,27 @@ CodeGenerator::emitArrayPush(LInstruction* lir, const MArrayPush* mir, Register
     OutOfLineCode* ool = oolCallVM(ArrayPushDenseInfo, lir, ArgList(obj, value), StoreRegisterTo(length));
 
     RegisterOrInt32Constant key = RegisterOrInt32Constant(length);
-    if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
-        // Load elements and length.
-        masm.loadPtr(Address(obj, NativeObject::offsetOfElements()), elementsTemp);
-        masm.load32(Address(elementsTemp, ObjectElements::offsetOfLength()), length);
 
-        // Guard length == initializedLength.
-        Address initLength(elementsTemp, ObjectElements::offsetOfInitializedLength());
-        masm.branch32(Assembler::NotEqual, initLength, key, ool->entry());
+    // Load elements and length.
+    masm.loadPtr(Address(obj, NativeObject::offsetOfElements()), elementsTemp);
+    masm.load32(Address(elementsTemp, ObjectElements::offsetOfLength()), length);
 
-        // Guard length < capacity.
-        Address capacity(elementsTemp, ObjectElements::offsetOfCapacity());
-        masm.branch32(Assembler::BelowOrEqual, capacity, key, ool->entry());
+    // Guard length == initializedLength.
+    Address initLength(elementsTemp, ObjectElements::offsetOfInitializedLength());
+    masm.branch32(Assembler::NotEqual, initLength, key, ool->entry());
 
-        // Do the store.
-        masm.storeConstantOrRegister(value, BaseIndex(elementsTemp, length, TimesEight));
-    } else {
-        // Load initialized length.
-        masm.load32(Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()), length);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), length);
+    // Guard length < capacity.
+    Address capacity(elementsTemp, ObjectElements::offsetOfCapacity());
+    masm.branch32(Assembler::BelowOrEqual, capacity, key, ool->entry());
 
-        // Guard length == initializedLength.
-        Address lengthAddr(obj, UnboxedArrayObject::offsetOfLength());
-        masm.branch32(Assembler::NotEqual, lengthAddr, key, ool->entry());
-
-        // Guard length < capacity.
-        masm.checkUnboxedArrayCapacity(obj, key, elementsTemp, ool->entry());
-
-        // Load elements and do the store.
-        masm.loadPtr(Address(obj, UnboxedArrayObject::offsetOfElements()), elementsTemp);
-        size_t elemSize = UnboxedTypeSize(mir->unboxedType());
-        BaseIndex addr(elementsTemp, length, ScaleFromElemWidth(elemSize));
-        masm.storeUnboxedProperty(addr, mir->unboxedType(), value, nullptr);
-    }
+    // Do the store.
+    masm.storeConstantOrRegister(value, BaseIndex(elementsTemp, length, TimesEight));
 
     masm.inc32(&key);
 
     // Update length and initialized length.
-    if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
-        masm.store32(length, Address(elementsTemp, ObjectElements::offsetOfLength()));
-        masm.store32(length, Address(elementsTemp, ObjectElements::offsetOfInitializedLength()));
-    } else {
-        masm.store32(length, Address(obj, UnboxedArrayObject::offsetOfLength()));
-        masm.add32(Imm32(1), Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()));
-    }
+    masm.store32(length, Address(elementsTemp, ObjectElements::offsetOfLength()));
+    masm.store32(length, Address(elementsTemp, ObjectElements::offsetOfInitializedLength()));
 
     masm.bind(ool->rejoin());
 }
@@ -8934,11 +8671,11 @@ CodeGenerator::visitIteratorStartO(LIteratorStartO* lir)
     masm.loadPtr(Address(niTemp, offsetof(NativeIterator, guard_array)), temp2);
 
     // Compare object with the first receiver guard. The last iterator can only
-    // match for native objects and unboxed objects.
+    // match for native objects.
     {
         Address groupAddr(temp2, offsetof(ReceiverGuard, group));
         Address shapeAddr(temp2, offsetof(ReceiverGuard, shape));
-        Label guardDone, shapeMismatch, noExpando;
+        Label guardDone, shapeMismatch;
         masm.loadObjShape(obj, temp1);
         masm.branchPtr(Assembler::NotEqual, shapeAddr, temp1, &shapeMismatch);
 
@@ -8950,12 +8687,6 @@ CodeGenerator::visitIteratorStartO(LIteratorStartO* lir)
         masm.bind(&shapeMismatch);
         masm.loadObjGroup(obj, temp1);
         masm.branchPtr(Assembler::NotEqual, groupAddr, temp1, ool->entry());
-        masm.loadPtr(Address(obj, UnboxedPlainObject::offsetOfExpando()), temp1);
-        masm.branchTestPtr(Assembler::Zero, temp1, temp1, &noExpando);
-        branchIfNotEmptyObjectElements(temp1, ool->entry());
-        masm.loadObjShape(temp1, temp1);
-        masm.bind(&noExpando);
-        masm.branchPtr(Assembler::NotEqual, shapeAddr, temp1, ool->entry());
         masm.bind(&guardDone);
     }
 
@@ -10590,22 +10321,11 @@ CodeGenerator::visitLoadElementHole(LLoadElementHole* lir)
     else
         masm.branch32(Assembler::BelowOrEqual, initLength, ToRegister(lir->index()), &undefined);
 
-    if (mir->unboxedType() != JSVAL_TYPE_MAGIC) {
-        size_t width = UnboxedTypeSize(mir->unboxedType());
-        if (lir->index()->isConstant()) {
-            Address addr(elements, ToInt32(lir->index()) * width);
-            masm.loadUnboxedProperty(addr, mir->unboxedType(), out);
-        } else {
-            BaseIndex addr(elements, ToRegister(lir->index()), ScaleFromElemWidth(width));
-            masm.loadUnboxedProperty(addr, mir->unboxedType(), out);
-        }
+    if (lir->index()->isConstant()) {
+        NativeObject::elementsSizeMustNotOverflow();
+        masm.loadValue(Address(elements, ToInt32(lir->index()) * sizeof(Value)), out);
     } else {
-        if (lir->index()->isConstant()) {
-            NativeObject::elementsSizeMustNotOverflow();
-            masm.loadValue(Address(elements, ToInt32(lir->index()) * sizeof(Value)), out);
-        } else {
-            masm.loadValue(BaseObjectElementIndex(elements, ToRegister(lir->index())), out);
-        }
+        masm.loadValue(BaseObjectElementIndex(elements, ToRegister(lir->index())), out);
     }
 
     // If a hole check is needed, and the value wasn't a hole, we're done.
@@ -10983,7 +10703,7 @@ CodeGenerator::visitInArray(LInArray* lir)
         }
 
         masm.branch32(Assembler::BelowOrEqual, initLength, Imm32(index), failedInitLength);
-        if (mir->needsHoleCheck() && mir->unboxedType() == JSVAL_TYPE_MAGIC) {
+        if (mir->needsHoleCheck()) {
             NativeObject::elementsSizeMustNotOverflow();
             Address address = Address(elements, index * sizeof(Value));
             masm.branchTestMagic(Assembler::Equal, address, &falseBranch);
@@ -10996,7 +10716,7 @@ CodeGenerator::visitInArray(LInArray* lir)
             failedInitLength = &negativeIntCheck;
 
         masm.branch32(Assembler::BelowOrEqual, initLength, index, failedInitLength);
-        if (mir->needsHoleCheck() && mir->unboxedType() == JSVAL_TYPE_MAGIC) {
+        if (mir->needsHoleCheck()) {
             BaseIndex address = BaseIndex(elements, ToRegister(lir->index()), TimesEight);
             masm.branchTestMagic(Assembler::Equal, address, &falseBranch);
         }
diff --git a/js/src/jit/CodeGenerator.h b/js/src/jit/CodeGenerator.h
index b226f6cc9..b5f170d84 100644
--- a/js/src/jit/CodeGenerator.h
+++ b/js/src/jit/CodeGenerator.h
@@ -148,8 +148,6 @@ class CodeGenerator final : public CodeGeneratorSpecific
     void visitMaybeCopyElementsForWrite(LMaybeCopyElementsForWrite* lir);
     void visitGuardObjectIdentity(LGuardObjectIdentity* guard);
     void visitGuardReceiverPolymorphic(LGuardReceiverPolymorphic* lir);
-    void visitGuardUnboxedExpando(LGuardUnboxedExpando* lir);
-    void visitLoadUnboxedExpando(LLoadUnboxedExpando* lir);
     void visitTypeBarrierV(LTypeBarrierV* lir);
     void visitTypeBarrierO(LTypeBarrierO* lir);
     void visitMonitorTypes(LMonitorTypes* lir);
@@ -236,10 +234,6 @@ class CodeGenerator final : public CodeGeneratorSpecific
     void visitSubstr(LSubstr* lir);
     void visitInitializedLength(LInitializedLength* lir);
     void visitSetInitializedLength(LSetInitializedLength* lir);
-    void visitUnboxedArrayLength(LUnboxedArrayLength* lir);
-    void visitUnboxedArrayInitializedLength(LUnboxedArrayInitializedLength* lir);
-    void visitIncrementUnboxedArrayInitializedLength(LIncrementUnboxedArrayInitializedLength* lir);
-    void visitSetUnboxedArrayInitializedLength(LSetUnboxedArrayInitializedLength* lir);
     void visitNotO(LNotO* ins);
     void visitNotV(LNotV* ins);
     void visitBoundsCheck(LBoundsCheck* lir);
@@ -310,7 +304,6 @@ class CodeGenerator final : public CodeGeneratorSpecific
     void visitFallibleStoreElementV(LFallibleStoreElementV* lir);
     void visitFallibleStoreElementT(LFallibleStoreElementT* lir);
     void visitStoreUnboxedPointer(LStoreUnboxedPointer* lir);
-    void visitConvertUnboxedObjectToNative(LConvertUnboxedObjectToNative* lir);
     void emitArrayPopShift(LInstruction* lir, const MArrayPopShift* mir, Register obj,
                            Register elementsTemp, Register lengthTemp, TypedOrValueRegister out);
     void visitArrayPopShiftV(LArrayPopShiftV* lir);
diff --git a/js/src/jit/IonAnalysis.cpp b/js/src/jit/IonAnalysis.cpp
index d255c32a8..41c71c9c3 100644
--- a/js/src/jit/IonAnalysis.cpp
+++ b/js/src/jit/IonAnalysis.cpp
@@ -3515,8 +3515,6 @@ PassthroughOperand(MDefinition* def)
         return def->toConvertElementsToDoubles()->elements();
     if (def->isMaybeCopyElementsForWrite())
         return def->toMaybeCopyElementsForWrite()->object();
-    if (def->isConvertUnboxedObjectToNative())
-        return def->toConvertUnboxedObjectToNative()->object();
     return nullptr;
 }
 
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index 54d05cac4..a54a58add 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -32,7 +32,6 @@
 #include "vm/EnvironmentObject-inl.h"
 #include "vm/NativeObject-inl.h"
 #include "vm/ObjectGroup-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -2219,6 +2218,8 @@ IonBuilder::inspectOpcode(JSOp op)
         // update that stale value.
 #endif
       default:
+	    // Any unused opcodes and JSOP_LIMIT will end up here without having
+        // to explicitly specify
         break;
     }
 
@@ -6392,7 +6393,7 @@ IonBuilder::createThisScriptedSingleton(JSFunction* target, MDefinition* callee)
     JSObject* templateObject = inspector->getTemplateObject(pc);
     if (!templateObject)
         return nullptr;
-    if (!templateObject->is<PlainObject>() && !templateObject->is<UnboxedPlainObject>())
+    if (!templateObject->is<PlainObject>())
         return nullptr;
     if (templateObject->staticPrototype() != proto)
         return nullptr;
@@ -6429,7 +6430,7 @@ IonBuilder::createThisScriptedBaseline(MDefinition* callee)
     JSObject* templateObject = inspector->getTemplateObject(pc);
     if (!templateObject)
         return nullptr;
-    if (!templateObject->is<PlainObject>() && !templateObject->is<UnboxedPlainObject>())
+    if (!templateObject->is<PlainObject>())
         return nullptr;
 
     Shape* shape = target->lookupPure(compartment->runtime()->names().prototype);
@@ -7337,12 +7338,6 @@ IonBuilder::newArrayTryTemplateObject(bool* emitted, JSObject* templateObject, u
     if (!templateObject)
         return true;
 
-    if (templateObject->is<UnboxedArrayObject>()) {
-        MOZ_ASSERT(templateObject->as<UnboxedArrayObject>().capacity() >= length);
-        if (!templateObject->as<UnboxedArrayObject>().hasInlineElements())
-            return true;
-    }
-
     MOZ_ASSERT(length <= NativeObject::MAX_DENSE_ELEMENTS_COUNT);
 
     size_t arraySlots =
@@ -7598,7 +7593,6 @@ IonBuilder::jsop_initelem_array()
     // intializer, and that arrays are marked as non-packed when writing holes
     // to them during initialization.
     bool needStub = false;
-    JSValueType unboxedType = JSVAL_TYPE_MAGIC;
     if (shouldAbortOnPreliminaryGroups(obj)) {
         needStub = true;
     } else if (!obj->resultTypeSet() ||
@@ -7609,12 +7603,6 @@ IonBuilder::jsop_initelem_array()
     } else {
         MOZ_ASSERT(obj->resultTypeSet()->getObjectCount() == 1);
         TypeSet::ObjectKey* initializer = obj->resultTypeSet()->getObject(0);
-        if (initializer->clasp() == &UnboxedArrayObject::class_) {
-            if (initializer->group()->unboxedLayout().nativeGroup())
-                needStub = true;
-            else
-                unboxedType = initializer->group()->unboxedLayout().elementType();
-        }
         if (value->type() == MIRType::MagicHole) {
             if (!initializer->hasFlags(constraints(), OBJECT_FLAG_NON_PACKED))
                 needStub = true;
@@ -7634,60 +7622,46 @@ IonBuilder::jsop_initelem_array()
         return resumeAfter(store);
     }
 
-    return initializeArrayElement(obj, index, value, unboxedType, /* addResumePoint = */ true);
+    return initializeArrayElement(obj, index, value, /* addResumePoint = */ true);
 }
 
 bool
 IonBuilder::initializeArrayElement(MDefinition* obj, size_t index, MDefinition* value,
-                                   JSValueType unboxedType,
                                    bool addResumePointAndIncrementInitializedLength)
 {
     MConstant* id = MConstant::New(alloc(), Int32Value(index));
     current->add(id);
 
     // Get the elements vector.
-    MElements* elements = MElements::New(alloc(), obj, unboxedType != JSVAL_TYPE_MAGIC);
+    MElements* elements = MElements::New(alloc(), obj);
     current->add(elements);
 
-    if (unboxedType != JSVAL_TYPE_MAGIC) {
-        // Note: storeUnboxedValue takes care of any post barriers on the value.
-        storeUnboxedValue(obj, elements, 0, id, unboxedType, value, /* preBarrier = */ false);
-
-        if (addResumePointAndIncrementInitializedLength) {
-            MInstruction* increment = MIncrementUnboxedArrayInitializedLength::New(alloc(), obj);
-            current->add(increment);
-
-            if (!resumeAfter(increment))
-                return false;
-        }
-    } else {
-        if (NeedsPostBarrier(value))
-            current->add(MPostWriteBarrier::New(alloc(), obj, value));
+    if (NeedsPostBarrier(value))
+        current->add(MPostWriteBarrier::New(alloc(), obj, value));
 
-        if ((obj->isNewArray() && obj->toNewArray()->convertDoubleElements()) ||
-            (obj->isNullarySharedStub() &&
-            obj->resultTypeSet()->convertDoubleElements(constraints()) == TemporaryTypeSet::AlwaysConvertToDoubles))
-        {
-            MInstruction* valueDouble = MToDouble::New(alloc(), value);
-            current->add(valueDouble);
-            value = valueDouble;
-        }
+    if ((obj->isNewArray() && obj->toNewArray()->convertDoubleElements()) ||
+        (obj->isNullarySharedStub() &&
+        obj->resultTypeSet()->convertDoubleElements(constraints()) == TemporaryTypeSet::AlwaysConvertToDoubles))
+    {
+        MInstruction* valueDouble = MToDouble::New(alloc(), value);
+        current->add(valueDouble);
+        value = valueDouble;
+    }
 
-        // Store the value.
-        MStoreElement* store = MStoreElement::New(alloc(), elements, id, value,
+    // Store the value.
+    MStoreElement* store = MStoreElement::New(alloc(), elements, id, value,
                                                   /* needsHoleCheck = */ false);
-        current->add(store);
+    current->add(store);
 
-        if (addResumePointAndIncrementInitializedLength) {
-            // Update the initialized length. (The template object for this
-            // array has the array's ultimate length, so the length field is
-            // already correct: no updating needed.)
-            MSetInitializedLength* initLength = MSetInitializedLength::New(alloc(), elements, id);
-            current->add(initLength);
+    if (addResumePointAndIncrementInitializedLength) {
+        // Update the initialized length. (The template object for this
+        // array has the array's ultimate length, so the length field is
+        // already correct: no updating needed.)
+        MSetInitializedLength* initLength = MSetInitializedLength::New(alloc(), elements, id);
+        current->add(initLength);
 
-            if (!resumeAfter(initLength))
-                return false;
-        }
+        if (!resumeAfter(initLength))
+            return false;
     }
 
     return true;
@@ -7718,8 +7692,6 @@ IonBuilder::jsop_initprop(PropertyName* name)
             if (templateObject->is<PlainObject>()) {
                 if (!templateObject->as<PlainObject>().containsPure(name))
                     useSlowPath = true;
-            } else {
-                MOZ_ASSERT(templateObject->as<UnboxedPlainObject>().layout().lookup(name));
             }
         } else {
             useSlowPath = true;
@@ -8178,9 +8150,7 @@ IonBuilder::maybeMarkEmpty(MDefinition* ins)
 static bool
 ClassHasEffectlessLookup(const Class* clasp)
 {
-    return (clasp == &UnboxedPlainObject::class_) ||
-           (clasp == &UnboxedArrayObject::class_) ||
-           IsTypedObjectClass(clasp) ||
+    return IsTypedObjectClass(clasp) ||
            (clasp->isNative() && !clasp->getOpsLookupProperty());
 }
 
@@ -9012,8 +8982,6 @@ IonBuilder::jsop_getelem()
     }
 
     obj = maybeUnboxForPropertyAccess(obj);
-    if (obj->type() == MIRType::Object)
-        obj = convertUnboxedObjects(obj);
 
     bool emitted = false;
 
@@ -9458,12 +9426,9 @@ IonBuilder::getElemTryDense(bool* emitted, MDefinition* obj, MDefinition* index)
 {
     MOZ_ASSERT(*emitted == false);
 
-    JSValueType unboxedType = UnboxedArrayElementType(constraints(), obj, index);
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        if (!ElementAccessIsDenseNative(constraints(), obj, index)) {
-            trackOptimizationOutcome(TrackedOutcome::AccessNotDense);
-            return true;
-        }
+    if (!ElementAccessIsDenseNative(constraints(), obj, index)) {
+        trackOptimizationOutcome(TrackedOutcome::AccessNotDense);
+        return true;
     }
 
     // Don't generate a fast path if there have been bounds check failures
@@ -9480,7 +9445,7 @@ IonBuilder::getElemTryDense(bool* emitted, MDefinition* obj, MDefinition* index)
         return true;
     }
 
-    if (!jsop_getelem_dense(obj, index, unboxedType))
+    if (!jsop_getelem_dense(obj, index))
         return false;
 
     trackOptimizationSuccess();
@@ -9832,7 +9797,7 @@ IonBuilder::computeHeapType(const TemporaryTypeSet* objTypes, const jsid id)
 }
 
 bool
-IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index, JSValueType unboxedType)
+IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index)
 {
     TemporaryTypeSet* types = bytecodeTypes(pc);
 
@@ -9856,7 +9821,7 @@ IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index, JSValueType
         !ElementAccessHasExtraIndexedProperty(this, obj);
 
     MIRType knownType = MIRType::Value;
-    if (unboxedType == JSVAL_TYPE_MAGIC && barrier == BarrierKind::NoBarrier)
+    if (barrier == BarrierKind::NoBarrier)
         knownType = GetElemKnownType(needsHoleCheck, types);
 
     // Ensure index is an integer.
@@ -9865,13 +9830,13 @@ IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index, JSValueType
     index = idInt32;
 
     // Get the elements vector.
-    MInstruction* elements = MElements::New(alloc(), obj, unboxedType != JSVAL_TYPE_MAGIC);
+    MInstruction* elements = MElements::New(alloc(), obj);
     current->add(elements);
 
     // Note: to help GVN, use the original MElements instruction and not
     // MConvertElementsToDoubles as operand. This is fine because converting
     // elements to double does not change the initialized length.
-    MInstruction* initLength = initializedLength(obj, elements, unboxedType);
+    MInstruction* initLength = initializedLength(obj, elements);
 
     // If we can load the element as a definite double, make sure to check that
     // the array has been converted to homogenous doubles first.
@@ -9887,7 +9852,6 @@ IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index, JSValueType
     }
 
     bool loadDouble =
-        unboxedType == JSVAL_TYPE_MAGIC &&
         barrier == BarrierKind::NoBarrier &&
         loopDepth_ &&
         inBounds &&
@@ -9906,18 +9870,13 @@ IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index, JSValueType
         // hoisting.
         index = addBoundsCheck(index, initLength);
 
-        if (unboxedType != JSVAL_TYPE_MAGIC) {
-            load = loadUnboxedValue(elements, 0, index, unboxedType, barrier, types);
-        } else {
-            load = MLoadElement::New(alloc(), elements, index, needsHoleCheck, loadDouble);
-            current->add(load);
-        }
+        load = MLoadElement::New(alloc(), elements, index, needsHoleCheck, loadDouble);
+        current->add(load);
     } else {
         // This load may return undefined, so assume that we *can* read holes,
         // or that we can read out-of-bounds accesses. In this case, the bounds
         // check is part of the opcode.
-        load = MLoadElementHole::New(alloc(), elements, index, initLength,
-                                     unboxedType, needsHoleCheck);
+        load = MLoadElementHole::New(alloc(), elements, index, initLength, needsHoleCheck);
         current->add(load);
 
         // If maybeUndefined was true, the typeset must have undefined, and
@@ -9927,8 +9886,7 @@ IonBuilder::jsop_getelem_dense(MDefinition* obj, MDefinition* index, JSValueType
     }
 
     if (knownType != MIRType::Value) {
-        if (unboxedType == JSVAL_TYPE_MAGIC)
-            load->setResultType(knownType);
+        load->setResultType(knownType);
         load->setResultTypeSet(types);
     }
 
@@ -10137,7 +10095,7 @@ IonBuilder::jsop_setelem()
 
     MDefinition* value = current->pop();
     MDefinition* index = current->pop();
-    MDefinition* object = convertUnboxedObjects(current->pop());
+    MDefinition* object = current->pop();
 
     trackTypeInfo(TrackedTypeSite::Receiver, object->type(), object->resultTypeSet());
     trackTypeInfo(TrackedTypeSite::Index, index->type(), index->resultTypeSet());
@@ -10375,12 +10333,9 @@ IonBuilder::setElemTryDense(bool* emitted, MDefinition* object,
 {
     MOZ_ASSERT(*emitted == false);
 
-    JSValueType unboxedType = UnboxedArrayElementType(constraints(), object, index);
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        if (!ElementAccessIsDenseNative(constraints(), object, index)) {
-            trackOptimizationOutcome(TrackedOutcome::AccessNotDense);
-            return true;
-        }
+    if (!ElementAccessIsDenseNative(constraints(), object, index)) {
+        trackOptimizationOutcome(TrackedOutcome::AccessNotDense);
+        return true;
     }
 
     if (PropertyWriteNeedsTypeBarrier(alloc(), constraints(), current,
@@ -10414,7 +10369,7 @@ IonBuilder::setElemTryDense(bool* emitted, MDefinition* object,
     }
 
     // Emit dense setelem variant.
-    if (!jsop_setelem_dense(conversion, object, index, value, unboxedType, writeHole, emitted))
+    if (!jsop_setelem_dense(conversion, object, index, value, writeHole, emitted))
         return false;
 
     if (!*emitted) {
@@ -10504,13 +10459,11 @@ IonBuilder::setElemTryCache(bool* emitted, MDefinition* object,
 bool
 IonBuilder::jsop_setelem_dense(TemporaryTypeSet::DoubleConversion conversion,
                                MDefinition* obj, MDefinition* id, MDefinition* value,
-                               JSValueType unboxedType, bool writeHole, bool* emitted)
+                               bool writeHole, bool* emitted)
 {
     MOZ_ASSERT(*emitted == false);
 
-    MIRType elementType = MIRType::None;
-    if (unboxedType == JSVAL_TYPE_MAGIC)
-        elementType = DenseNativeElementType(constraints(), obj);
+    MIRType elementType = DenseNativeElementType(constraints(), obj);
     bool packed = ElementAccessIsPacked(constraints(), obj);
 
     // Writes which are on holes in the object do not have to bail out if they
@@ -10540,7 +10493,7 @@ IonBuilder::jsop_setelem_dense(TemporaryTypeSet::DoubleConversion conversion,
     obj = addMaybeCopyElementsForWrite(obj, /* checkNative = */ false);
 
     // Get the elements vector.
-    MElements* elements = MElements::New(alloc(), obj, unboxedType != JSVAL_TYPE_MAGIC);
+    MElements* elements = MElements::New(alloc(), obj);
     current->add(elements);
 
     // Ensure the value is a double, if double conversion might be needed.
@@ -10577,7 +10530,7 @@ IonBuilder::jsop_setelem_dense(TemporaryTypeSet::DoubleConversion conversion,
     MInstruction* store;
     MStoreElementCommon* common = nullptr;
     if (writeHole && hasNoExtraIndexedProperty && !mayBeFrozen) {
-        MStoreElementHole* ins = MStoreElementHole::New(alloc(), obj, elements, id, newValue, unboxedType);
+        MStoreElementHole* ins = MStoreElementHole::New(alloc(), obj, elements, id, newValue);
         store = ins;
         common = ins;
 
@@ -10589,27 +10542,23 @@ IonBuilder::jsop_setelem_dense(TemporaryTypeSet::DoubleConversion conversion,
 
         bool strict = IsStrictSetPC(pc);
         MFallibleStoreElement* ins = MFallibleStoreElement::New(alloc(), obj, elements, id,
-                                                                newValue, unboxedType, strict);
+                                                                newValue, strict);
         store = ins;
         common = ins;
 
         current->add(ins);
         current->push(value);
     } else {
-        MInstruction* initLength = initializedLength(obj, elements, unboxedType);
+        MInstruction* initLength = initializedLength(obj, elements);
 
         id = addBoundsCheck(id, initLength);
         bool needsHoleCheck = !packed && !hasNoExtraIndexedProperty;
 
-        if (unboxedType != JSVAL_TYPE_MAGIC) {
-            store = storeUnboxedValue(obj, elements, 0, id, unboxedType, newValue);
-        } else {
-            MStoreElement* ins = MStoreElement::New(alloc(), elements, id, newValue, needsHoleCheck);
-            store = ins;
-            common = ins;
+        MStoreElement* ins = MStoreElement::New(alloc(), elements, id, newValue, needsHoleCheck);
+        store = ins;
+        common = ins;
 
-            current->add(store);
-        }
+        current->add(store);
 
         current->push(value);
     }
@@ -10727,18 +10676,6 @@ IonBuilder::jsop_length_fastPath()
             return true;
         }
 
-        // Compute the length for unboxed array objects.
-        if (UnboxedArrayElementType(constraints(), obj, nullptr) != JSVAL_TYPE_MAGIC &&
-            !objTypes->hasObjectFlags(constraints(), OBJECT_FLAG_LENGTH_OVERFLOW))
-        {
-            current->pop();
-
-            MUnboxedArrayLength* length = MUnboxedArrayLength::New(alloc(), obj);
-            current->add(length);
-            current->push(length);
-            return true;
-        }
-
         // Compute the length for array typed objects.
         TypedObjectPrediction prediction = typedObjectPrediction(obj);
         if (!prediction.isUseless()) {
@@ -10972,11 +10909,8 @@ IonBuilder::getDefiniteSlot(TemporaryTypeSet* types, PropertyName* name, uint32_
         }
 
         // Definite slots will always be fixed slots when they are in the
-        // allowable range for fixed slots, except for objects which were
-        // converted from unboxed objects and have a smaller allocation size.
+        // allowable range for fixed slots.
         size_t nfixed = NativeObject::MAX_FIXED_SLOTS;
-        if (ObjectGroup* group = key->group()->maybeOriginalUnboxedGroup())
-            nfixed = gc::GetGCKindSlots(group->unboxedLayout().getAllocKind());
 
         uint32_t propertySlot = property.maybeTypes()->definiteSlot();
         if (slot == UINT32_MAX) {
@@ -10991,65 +10925,6 @@ IonBuilder::getDefiniteSlot(TemporaryTypeSet* types, PropertyName* name, uint32_
     return slot;
 }
 
-uint32_t
-IonBuilder::getUnboxedOffset(TemporaryTypeSet* types, PropertyName* name, JSValueType* punboxedType)
-{
-    if (!types || types->unknownObject() || !types->objectOrSentinel()) {
-        trackOptimizationOutcome(TrackedOutcome::NoTypeInfo);
-        return UINT32_MAX;
-    }
-
-    uint32_t offset = UINT32_MAX;
-
-    for (size_t i = 0; i < types->getObjectCount(); i++) {
-        TypeSet::ObjectKey* key = types->getObject(i);
-        if (!key)
-            continue;
-
-        if (key->unknownProperties()) {
-            trackOptimizationOutcome(TrackedOutcome::UnknownProperties);
-            return UINT32_MAX;
-        }
-
-        if (key->isSingleton()) {
-            trackOptimizationOutcome(TrackedOutcome::Singleton);
-            return UINT32_MAX;
-        }
-
-        UnboxedLayout* layout = key->group()->maybeUnboxedLayout();
-        if (!layout) {
-            trackOptimizationOutcome(TrackedOutcome::NotUnboxed);
-            return UINT32_MAX;
-        }
-
-        const UnboxedLayout::Property* property = layout->lookup(name);
-        if (!property) {
-            trackOptimizationOutcome(TrackedOutcome::StructNoField);
-            return UINT32_MAX;
-        }
-
-        if (layout->nativeGroup()) {
-            trackOptimizationOutcome(TrackedOutcome::UnboxedConvertedToNative);
-            return UINT32_MAX;
-        }
-
-        key->watchStateChangeForUnboxedConvertedToNative(constraints());
-
-        if (offset == UINT32_MAX) {
-            offset = property->offset;
-            *punboxedType = property->type;
-        } else if (offset != property->offset) {
-            trackOptimizationOutcome(TrackedOutcome::InconsistentFieldOffset);
-            return UINT32_MAX;
-        } else if (*punboxedType != property->type) {
-            trackOptimizationOutcome(TrackedOutcome::InconsistentFieldType);
-            return UINT32_MAX;
-        }
-    }
-
-    return offset;
-}
-
 bool
 IonBuilder::jsop_runonce()
 {
@@ -11496,8 +11371,6 @@ IonBuilder::jsop_getprop(PropertyName* name)
     }
 
     obj = maybeUnboxForPropertyAccess(obj);
-    if (obj->type() == MIRType::Object)
-        obj = convertUnboxedObjects(obj);
 
     BarrierKind barrier = PropertyReadNeedsTypeBarrier(analysisContext, constraints(),
                                                        obj, name, types);
@@ -11569,11 +11442,6 @@ IonBuilder::jsop_getprop(PropertyName* name)
         if (!getPropTryDefiniteSlot(&emitted, obj, name, barrier, types) || emitted)
             return emitted;
 
-        // Try to emit loads from unboxed objects.
-        trackOptimizationAttempt(TrackedStrategy::GetProp_Unboxed);
-        if (!getPropTryUnboxed(&emitted, obj, name, barrier, types) || emitted)
-            return emitted;
-
         // Try to inline a common property getter, or make a call.
         trackOptimizationAttempt(TrackedStrategy::GetProp_CommonGetter);
         if (!getPropTryCommonGetter(&emitted, obj, name, types) || emitted)
@@ -11939,49 +11807,6 @@ IonBuilder::getPropTryComplexPropOfTypedObject(bool* emitted,
                                   fieldPrediction, fieldTypeObj);
 }
 
-MDefinition*
-IonBuilder::convertUnboxedObjects(MDefinition* obj)
-{
-    // If obj might be in any particular unboxed group which should be
-    // converted to a native representation, perform that conversion. This does
-    // not guarantee the object will not have such a group afterwards, if the
-    // object's possible groups are not precisely known.
-    TemporaryTypeSet* types = obj->resultTypeSet();
-    if (!types || types->unknownObject() || !types->objectOrSentinel())
-        return obj;
-
-    BaselineInspector::ObjectGroupVector list(alloc());
-    for (size_t i = 0; i < types->getObjectCount(); i++) {
-        TypeSet::ObjectKey* key = obj->resultTypeSet()->getObject(i);
-        if (!key || !key->isGroup())
-            continue;
-
-        if (UnboxedLayout* layout = key->group()->maybeUnboxedLayout()) {
-            AutoEnterOOMUnsafeRegion oomUnsafe;
-            if (layout->nativeGroup() && !list.append(key->group()))
-                oomUnsafe.crash("IonBuilder::convertUnboxedObjects");
-        }
-    }
-
-    return convertUnboxedObjects(obj, list);
-}
-
-MDefinition*
-IonBuilder::convertUnboxedObjects(MDefinition* obj,
-                                  const BaselineInspector::ObjectGroupVector& list)
-{
-    for (size_t i = 0; i < list.length(); i++) {
-        ObjectGroup* group = list[i];
-        if (TemporaryTypeSet* types = obj->resultTypeSet()) {
-            if (!types->hasType(TypeSet::ObjectType(group)))
-                continue;
-        }
-        obj = MConvertUnboxedObjectToNative::New(alloc(), obj, group);
-        current->add(obj->toInstruction());
-    }
-    return obj;
-}
-
 bool
 IonBuilder::getPropTryDefiniteSlot(bool* emitted, MDefinition* obj, PropertyName* name,
                                    BarrierKind barrier, TemporaryTypeSet* types)
@@ -12066,111 +11891,14 @@ IonBuilder::getPropTryModuleNamespace(bool* emitted, MDefinition* obj, PropertyN
     return true;
 }
 
-MInstruction*
-IonBuilder::loadUnboxedProperty(MDefinition* obj, size_t offset, JSValueType unboxedType,
-                                BarrierKind barrier, TemporaryTypeSet* types)
-{
-    // loadUnboxedValue is designed to load any value as if it were contained in
-    // an array. Thus a property offset is converted to an index, when the
-    // object is reinterpreted as an array of properties of the same size.
-    size_t index = offset / UnboxedTypeSize(unboxedType);
-    MInstruction* indexConstant = MConstant::New(alloc(), Int32Value(index));
-    current->add(indexConstant);
-
-    return loadUnboxedValue(obj, UnboxedPlainObject::offsetOfData(),
-                            indexConstant, unboxedType, barrier, types);
-}
-
-MInstruction*
-IonBuilder::loadUnboxedValue(MDefinition* elements, size_t elementsOffset,
-                             MDefinition* index, JSValueType unboxedType,
-                             BarrierKind barrier, TemporaryTypeSet* types)
-{
-    MInstruction* load;
-    switch (unboxedType) {
-      case JSVAL_TYPE_BOOLEAN:
-        load = MLoadUnboxedScalar::New(alloc(), elements, index, Scalar::Uint8,
-                                       DoesNotRequireMemoryBarrier, elementsOffset);
-        load->setResultType(MIRType::Boolean);
-        break;
-
-      case JSVAL_TYPE_INT32:
-        load = MLoadUnboxedScalar::New(alloc(), elements, index, Scalar::Int32,
-                                       DoesNotRequireMemoryBarrier, elementsOffset);
-        load->setResultType(MIRType::Int32);
-        break;
-
-      case JSVAL_TYPE_DOUBLE:
-        load = MLoadUnboxedScalar::New(alloc(), elements, index, Scalar::Float64,
-                                       DoesNotRequireMemoryBarrier, elementsOffset,
-                                       /* canonicalizeDoubles = */ false);
-        load->setResultType(MIRType::Double);
-        break;
-
-      case JSVAL_TYPE_STRING:
-        load = MLoadUnboxedString::New(alloc(), elements, index, elementsOffset);
-        break;
-
-      case JSVAL_TYPE_OBJECT: {
-        MLoadUnboxedObjectOrNull::NullBehavior nullBehavior;
-        if (types->hasType(TypeSet::NullType()))
-            nullBehavior = MLoadUnboxedObjectOrNull::HandleNull;
-        else if (barrier != BarrierKind::NoBarrier)
-            nullBehavior = MLoadUnboxedObjectOrNull::BailOnNull;
-        else
-            nullBehavior = MLoadUnboxedObjectOrNull::NullNotPossible;
-        load = MLoadUnboxedObjectOrNull::New(alloc(), elements, index, nullBehavior,
-                                             elementsOffset);
-        break;
-      }
-
-      default:
-        MOZ_CRASH();
-    }
-
-    current->add(load);
-    return load;
-}
-
-bool
-IonBuilder::getPropTryUnboxed(bool* emitted, MDefinition* obj, PropertyName* name,
-                              BarrierKind barrier, TemporaryTypeSet* types)
-{
-    MOZ_ASSERT(*emitted == false);
-
-    JSValueType unboxedType;
-    uint32_t offset = getUnboxedOffset(obj->resultTypeSet(), name, &unboxedType);
-    if (offset == UINT32_MAX)
-        return true;
-
-    if (obj->type() != MIRType::Object) {
-        MGuardObject* guard = MGuardObject::New(alloc(), obj);
-        current->add(guard);
-        obj = guard;
-    }
-
-    MInstruction* load = loadUnboxedProperty(obj, offset, unboxedType, barrier, types);
-    current->push(load);
-
-    if (!pushTypeBarrier(load, types, barrier))
-        return false;
-
-    trackOptimizationSuccess();
-    *emitted = true;
-    return true;
-}
-
 MDefinition*
 IonBuilder::addShapeGuardsForGetterSetter(MDefinition* obj, JSObject* holder, Shape* holderShape,
                 const BaselineInspector::ReceiverVector& receivers,
-                const BaselineInspector::ObjectGroupVector& convertUnboxedGroups,
                 bool isOwnProperty)
 {
     MOZ_ASSERT(holder);
     MOZ_ASSERT(holderShape);
 
-    obj = convertUnboxedObjects(obj, convertUnboxedGroups);
-
     if (isOwnProperty) {
         MOZ_ASSERT(receivers.empty());
         return addShapeGuard(obj, holderShape, Bailout_ShapeGuard);
@@ -12194,10 +11922,8 @@ IonBuilder::getPropTryCommonGetter(bool* emitted, MDefinition* obj, PropertyName
     JSObject* foundProto = nullptr;
     bool isOwnProperty = false;
     BaselineInspector::ReceiverVector receivers(alloc());
-    BaselineInspector::ObjectGroupVector convertUnboxedGroups(alloc());
     if (!inspector->commonGetPropFunction(pc, &foundProto, &lastProperty, &commonGetter,
-                                          &globalShape, &isOwnProperty,
-                                          receivers, convertUnboxedGroups))
+                                          &globalShape, &isOwnProperty, receivers))
     {
         return true;
     }
@@ -12213,8 +11939,7 @@ IonBuilder::getPropTryCommonGetter(bool* emitted, MDefinition* obj, PropertyName
         // If type information is bad, we can still optimize the getter if we
         // shape guard.
         obj = addShapeGuardsForGetterSetter(obj, foundProto, lastProperty,
-                                            receivers, convertUnboxedGroups,
-                                            isOwnProperty);
+                                            receivers, isOwnProperty);
         if (!obj)
             return false;
     }
@@ -12381,15 +12106,12 @@ IonBuilder::getPropTryInlineAccess(bool* emitted, MDefinition* obj, PropertyName
     MOZ_ASSERT(*emitted == false);
 
     BaselineInspector::ReceiverVector receivers(alloc());
-    BaselineInspector::ObjectGroupVector convertUnboxedGroups(alloc());
-    if (!inspector->maybeInfoForPropertyOp(pc, receivers, convertUnboxedGroups))
+    if (!inspector->maybeInfoForPropertyOp(pc, receivers))
         return false;
 
     if (!canInlinePropertyOpShapes(receivers))
         return true;
 
-    obj = convertUnboxedObjects(obj, convertUnboxedGroups);
-
     MIRType rvalType = types->getKnownMIRType();
     if (barrier != BarrierKind::NoBarrier || IsNullOrUndefined(rvalType))
         rvalType = MIRType::Value;
@@ -12412,45 +12134,6 @@ IonBuilder::getPropTryInlineAccess(bool* emitted, MDefinition* obj, PropertyName
             return true;
         }
 
-        if (receivers[0].shape) {
-            // Monomorphic load from an unboxed object expando.
-            spew("Inlining monomorphic unboxed expando GETPROP");
-
-            obj = addGroupGuard(obj, receivers[0].group, Bailout_ShapeGuard);
-            obj = addUnboxedExpandoGuard(obj, /* hasExpando = */ true, Bailout_ShapeGuard);
-
-            MInstruction* expando = MLoadUnboxedExpando::New(alloc(), obj);
-            current->add(expando);
-
-            expando = addShapeGuard(expando, receivers[0].shape, Bailout_ShapeGuard);
-
-            Shape* shape = receivers[0].shape->searchLinear(NameToId(name));
-            MOZ_ASSERT(shape);
-
-            if (!loadSlot(expando, shape, rvalType, barrier, types))
-                return false;
-
-            trackOptimizationOutcome(TrackedOutcome::Monomorphic);
-            *emitted = true;
-            return true;
-        }
-
-        // Monomorphic load from an unboxed object.
-        ObjectGroup* group = receivers[0].group;
-        if (obj->resultTypeSet() && !obj->resultTypeSet()->hasType(TypeSet::ObjectType(group)))
-            return true;
-
-        obj = addGroupGuard(obj, group, Bailout_ShapeGuard);
-
-        const UnboxedLayout::Property* property = group->unboxedLayout().lookup(name);
-        MInstruction* load = loadUnboxedProperty(obj, property->offset, property->type, barrier, types);
-        current->push(load);
-
-        if (!pushTypeBarrier(load, types, barrier))
-            return false;
-
-        trackOptimizationOutcome(TrackedOutcome::Monomorphic);
-        *emitted = true;
         return true;
     }
 
@@ -12692,7 +12375,7 @@ bool
 IonBuilder::jsop_setprop(PropertyName* name)
 {
     MDefinition* value = current->pop();
-    MDefinition* obj = convertUnboxedObjects(current->pop());
+    MDefinition* obj = current->pop();
 
     bool emitted = false;
     startTrackingOptimizations();
@@ -12725,13 +12408,6 @@ IonBuilder::jsop_setprop(PropertyName* name)
     bool barrier = PropertyWriteNeedsTypeBarrier(alloc(), constraints(), current, &obj, name, &value,
                                                  /* canModify = */ true);
 
-    if (!forceInlineCaches()) {
-        // Try to emit stores to unboxed objects.
-        trackOptimizationAttempt(TrackedStrategy::SetProp_Unboxed);
-        if (!setPropTryUnboxed(&emitted, obj, name, value, barrier, objTypes) || emitted)
-            return emitted;
-    }
-
     // Add post barrier if needed. The instructions above manage any post
     // barriers they need directly.
     if (NeedsPostBarrier(value))
@@ -12765,10 +12441,8 @@ IonBuilder::setPropTryCommonSetter(bool* emitted, MDefinition* obj,
     JSObject* foundProto = nullptr;
     bool isOwnProperty;
     BaselineInspector::ReceiverVector receivers(alloc());
-    BaselineInspector::ObjectGroupVector convertUnboxedGroups(alloc());
     if (!inspector->commonSetPropFunction(pc, &foundProto, &lastProperty, &commonSetter,
-                                          &isOwnProperty,
-                                          receivers, convertUnboxedGroups))
+                                          &isOwnProperty, receivers))
     {
         trackOptimizationOutcome(TrackedOutcome::NoProtoFound);
         return true;
@@ -12783,8 +12457,7 @@ IonBuilder::setPropTryCommonSetter(bool* emitted, MDefinition* obj,
         // If type information is bad, we can still optimize the setter if we
         // shape guard.
         obj = addShapeGuardsForGetterSetter(obj, foundProto, lastProperty,
-                                            receivers, convertUnboxedGroups,
-                                            isOwnProperty);
+                                            receivers, isOwnProperty);
         if (!obj)
             return false;
     }
@@ -13039,100 +12712,6 @@ IonBuilder::setPropTryDefiniteSlot(bool* emitted, MDefinition* obj,
     return true;
 }
 
-MInstruction*
-IonBuilder::storeUnboxedProperty(MDefinition* obj, size_t offset, JSValueType unboxedType,
-                                 MDefinition* value)
-{
-    size_t scaledOffsetConstant = offset / UnboxedTypeSize(unboxedType);
-    MInstruction* scaledOffset = MConstant::New(alloc(), Int32Value(scaledOffsetConstant));
-    current->add(scaledOffset);
-
-    return storeUnboxedValue(obj, obj, UnboxedPlainObject::offsetOfData(),
-                             scaledOffset, unboxedType, value);
-}
-
-MInstruction*
-IonBuilder::storeUnboxedValue(MDefinition* obj, MDefinition* elements, int32_t elementsOffset,
-                              MDefinition* scaledOffset, JSValueType unboxedType,
-                              MDefinition* value, bool preBarrier /* = true */)
-{
-    MInstruction* store;
-    switch (unboxedType) {
-      case JSVAL_TYPE_BOOLEAN:
-        store = MStoreUnboxedScalar::New(alloc(), elements, scaledOffset, value, Scalar::Uint8,
-                                         MStoreUnboxedScalar::DontTruncateInput,
-                                         DoesNotRequireMemoryBarrier, elementsOffset);
-        break;
-
-      case JSVAL_TYPE_INT32:
-        store = MStoreUnboxedScalar::New(alloc(), elements, scaledOffset, value, Scalar::Int32,
-                                         MStoreUnboxedScalar::DontTruncateInput,
-                                         DoesNotRequireMemoryBarrier, elementsOffset);
-        break;
-
-      case JSVAL_TYPE_DOUBLE:
-        store = MStoreUnboxedScalar::New(alloc(), elements, scaledOffset, value, Scalar::Float64,
-                                         MStoreUnboxedScalar::DontTruncateInput,
-                                         DoesNotRequireMemoryBarrier, elementsOffset);
-        break;
-
-      case JSVAL_TYPE_STRING:
-        store = MStoreUnboxedString::New(alloc(), elements, scaledOffset, value,
-                                         elementsOffset, preBarrier);
-        break;
-
-      case JSVAL_TYPE_OBJECT:
-        MOZ_ASSERT(value->type() == MIRType::Object ||
-                   value->type() == MIRType::Null ||
-                   value->type() == MIRType::Value);
-        MOZ_ASSERT(!value->mightBeType(MIRType::Undefined),
-                   "MToObjectOrNull slow path is invalid for unboxed objects");
-        store = MStoreUnboxedObjectOrNull::New(alloc(), elements, scaledOffset, value, obj,
-                                               elementsOffset, preBarrier);
-        break;
-
-      default:
-        MOZ_CRASH();
-    }
-
-    current->add(store);
-    return store;
-}
-
-bool
-IonBuilder::setPropTryUnboxed(bool* emitted, MDefinition* obj,
-                              PropertyName* name, MDefinition* value,
-                              bool barrier, TemporaryTypeSet* objTypes)
-{
-    MOZ_ASSERT(*emitted == false);
-
-    if (barrier) {
-        trackOptimizationOutcome(TrackedOutcome::NeedsTypeBarrier);
-        return true;
-    }
-
-    JSValueType unboxedType;
-    uint32_t offset = getUnboxedOffset(obj->resultTypeSet(), name, &unboxedType);
-    if (offset == UINT32_MAX)
-        return true;
-
-    if (obj->type() != MIRType::Object) {
-        MGuardObject* guard = MGuardObject::New(alloc(), obj);
-        current->add(guard);
-        obj = guard;
-    }
-
-    MInstruction* store = storeUnboxedProperty(obj, offset, unboxedType, value);
-
-    current->push(value);
-
-    if (!resumeAfter(store))
-        return false;
-
-    *emitted = true;
-    return true;
-}
-
 bool
 IonBuilder::setPropTryInlineAccess(bool* emitted, MDefinition* obj,
                                    PropertyName* name, MDefinition* value,
@@ -13146,15 +12725,12 @@ IonBuilder::setPropTryInlineAccess(bool* emitted, MDefinition* obj,
     }
 
     BaselineInspector::ReceiverVector receivers(alloc());
-    BaselineInspector::ObjectGroupVector convertUnboxedGroups(alloc());
-    if (!inspector->maybeInfoForPropertyOp(pc, receivers, convertUnboxedGroups))
+    if (!inspector->maybeInfoForPropertyOp(pc, receivers))
         return false;
 
     if (!canInlinePropertyOpShapes(receivers))
         return true;
 
-    obj = convertUnboxedObjects(obj, convertUnboxedGroups);
-
     if (receivers.length() == 1) {
         if (!receivers[0].group) {
             // Monomorphic store to a native object.
@@ -13174,46 +12750,6 @@ IonBuilder::setPropTryInlineAccess(bool* emitted, MDefinition* obj,
             return true;
         }
 
-        if (receivers[0].shape) {
-            // Monomorphic store to an unboxed object expando.
-            spew("Inlining monomorphic unboxed expando SETPROP");
-
-            obj = addGroupGuard(obj, receivers[0].group, Bailout_ShapeGuard);
-            obj = addUnboxedExpandoGuard(obj, /* hasExpando = */ true, Bailout_ShapeGuard);
-
-            MInstruction* expando = MLoadUnboxedExpando::New(alloc(), obj);
-            current->add(expando);
-
-            expando = addShapeGuard(expando, receivers[0].shape, Bailout_ShapeGuard);
-
-            Shape* shape = receivers[0].shape->searchLinear(NameToId(name));
-            MOZ_ASSERT(shape);
-
-            bool needsBarrier = objTypes->propertyNeedsBarrier(constraints(), NameToId(name));
-            if (!storeSlot(expando, shape, value, needsBarrier))
-                return false;
-
-            trackOptimizationOutcome(TrackedOutcome::Monomorphic);
-            *emitted = true;
-            return true;
-        }
-
-        // Monomorphic store to an unboxed object.
-        spew("Inlining monomorphic unboxed SETPROP");
-
-        ObjectGroup* group = receivers[0].group;
-        if (!objTypes->hasType(TypeSet::ObjectType(group)))
-            return true;
-
-        obj = addGroupGuard(obj, group, Bailout_ShapeGuard);
-
-        const UnboxedLayout::Property* property = group->unboxedLayout().lookup(name);
-        storeUnboxedProperty(obj, property->offset, property->type, value);
-
-        current->push(value);
-
-        trackOptimizationOutcome(TrackedOutcome::Monomorphic);
-        *emitted = true;
         return true;
     }
 
@@ -13884,7 +13420,7 @@ IonBuilder::jsop_setaliasedvar(EnvironmentCoordinate ec)
 bool
 IonBuilder::jsop_in()
 {
-    MDefinition* obj = convertUnboxedObjects(current->pop());
+    MDefinition* obj = current->pop();
     MDefinition* id = current->pop();
 
     bool emitted = false;
@@ -13911,11 +13447,8 @@ IonBuilder::inTryDense(bool* emitted, MDefinition* obj, MDefinition* id)
     if (shouldAbortOnPreliminaryGroups(obj))
         return true;
 
-    JSValueType unboxedType = UnboxedArrayElementType(constraints(), obj, id);
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        if (!ElementAccessIsDenseNative(constraints(), obj, id))
-            return true;
-    }
+    if (!ElementAccessIsDenseNative(constraints(), obj, id))
+        return true;
 
     if (ElementAccessHasExtraIndexedProperty(this, obj))
         return true;
@@ -13930,10 +13463,10 @@ IonBuilder::inTryDense(bool* emitted, MDefinition* obj, MDefinition* id)
     id = idInt32;
 
     // Get the elements vector.
-    MElements* elements = MElements::New(alloc(), obj, unboxedType != JSVAL_TYPE_MAGIC);
+    MElements* elements = MElements::New(alloc(), obj);
     current->add(elements);
 
-    MInstruction* initLength = initializedLength(obj, elements, unboxedType);
+    MInstruction* initLength = initializedLength(obj, elements);
 
     // If there are no holes, speculate the InArray check will not fail.
     if (!needsHoleCheck && !failedBoundsCheck_) {
@@ -13943,8 +13476,7 @@ IonBuilder::inTryDense(bool* emitted, MDefinition* obj, MDefinition* id)
     }
 
     // Check if id < initLength and elem[id] not a hole.
-    MInArray* ins = MInArray::New(alloc(), elements, id, initLength, obj, needsHoleCheck,
-                                  unboxedType);
+    MInArray* ins = MInArray::New(alloc(), elements, id, initLength, obj, needsHoleCheck);
 
     current->add(ins);
     current->push(ins);
@@ -14241,19 +13773,6 @@ IonBuilder::addGroupGuard(MDefinition* obj, ObjectGroup* group, BailoutKind bail
 }
 
 MInstruction*
-IonBuilder::addUnboxedExpandoGuard(MDefinition* obj, bool hasExpando, BailoutKind bailoutKind)
-{
-    MGuardUnboxedExpando* guard = MGuardUnboxedExpando::New(alloc(), obj, hasExpando, bailoutKind);
-    current->add(guard);
-
-    // If a shape guard failed in the past, don't optimize group guards.
-    if (failedShapeGuard_)
-        guard->setNotMovable();
-
-    return guard;
-}
-
-MInstruction*
 IonBuilder::addGuardReceiverPolymorphic(MDefinition* obj,
                                         const BaselineInspector::ReceiverVector& receivers)
 {
@@ -14262,15 +13781,6 @@ IonBuilder::addGuardReceiverPolymorphic(MDefinition* obj,
             // Monomorphic guard on a native object.
             return addShapeGuard(obj, receivers[0].shape, Bailout_ShapeGuard);
         }
-
-        if (!receivers[0].shape) {
-            // Guard on an unboxed object that does not have an expando.
-            obj = addGroupGuard(obj, receivers[0].group, Bailout_ShapeGuard);
-            return addUnboxedExpandoGuard(obj, /* hasExpando = */ false, Bailout_ShapeGuard);
-        }
-
-        // Monomorphic receiver guards are not yet supported when the receiver
-        // is an unboxed object with an expando.
     }
 
     MGuardReceiverPolymorphic* guard = MGuardReceiverPolymorphic::New(alloc(), obj);
@@ -14644,32 +14154,24 @@ IonBuilder::constantInt(int32_t i)
 }
 
 MInstruction*
-IonBuilder::initializedLength(MDefinition* obj, MDefinition* elements, JSValueType unboxedType)
+IonBuilder::initializedLength(MDefinition* obj, MDefinition* elements)
 {
-    MInstruction* res;
-    if (unboxedType != JSVAL_TYPE_MAGIC)
-        res = MUnboxedArrayInitializedLength::New(alloc(), obj);
-    else
-        res = MInitializedLength::New(alloc(), elements);
+    MInstruction* res = MInitializedLength::New(alloc(), elements);
     current->add(res);
     return res;
 }
 
 MInstruction*
-IonBuilder::setInitializedLength(MDefinition* obj, JSValueType unboxedType, size_t count)
+IonBuilder::setInitializedLength(MDefinition* obj, size_t count)
 {
     MOZ_ASSERT(count);
 
-    MInstruction* res;
-    if (unboxedType != JSVAL_TYPE_MAGIC) {
-        res = MSetUnboxedArrayInitializedLength::New(alloc(), obj, constant(Int32Value(count)));
-    } else {
-        // MSetInitializedLength takes the index of the last element, rather
-        // than the count itself.
-        MInstruction* elements = MElements::New(alloc(), obj, /* unboxed = */ false);
-        current->add(elements);
-        res = MSetInitializedLength::New(alloc(), elements, constant(Int32Value(count - 1)));
-    }
+    // MSetInitializedLength takes the index of the last element, rather
+    // than the count itself.
+    MInstruction* elements = MElements::New(alloc(), obj, /* unboxed = */ false);
+    current->add(elements);
+    MInstruction* res = 
+	    MSetInitializedLength::New(alloc(), elements, constant(Int32Value(count - 1)));
     current->add(res);
     return res;
 }
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index f24ef30c8..dd40b4bd6 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -346,9 +346,8 @@ class IonBuilder
 
     MConstant* constant(const Value& v);
     MConstant* constantInt(int32_t i);
-    MInstruction* initializedLength(MDefinition* obj, MDefinition* elements,
-                                    JSValueType unboxedType);
-    MInstruction* setInitializedLength(MDefinition* obj, JSValueType unboxedType, size_t count);
+    MInstruction* initializedLength(MDefinition* obj, MDefinition* elements);
+    MInstruction* setInitializedLength(MDefinition* obj, size_t count);
 
     // Improve the type information at tests
     MOZ_MUST_USE bool improveTypesAtTest(MDefinition* ins, bool trueBranch, MTest* test);
@@ -401,7 +400,6 @@ class IonBuilder
     MInstruction* addBoundsCheck(MDefinition* index, MDefinition* length);
     MInstruction* addShapeGuard(MDefinition* obj, Shape* const shape, BailoutKind bailoutKind);
     MInstruction* addGroupGuard(MDefinition* obj, ObjectGroup* group, BailoutKind bailoutKind);
-    MInstruction* addUnboxedExpandoGuard(MDefinition* obj, bool hasExpando, BailoutKind bailoutKind);
     MInstruction* addSharedTypedArrayGuard(MDefinition* obj);
 
     MInstruction*
@@ -441,8 +439,6 @@ class IonBuilder
                                              BarrierKind barrier, TemporaryTypeSet* types);
     MOZ_MUST_USE bool getPropTryModuleNamespace(bool* emitted, MDefinition* obj, PropertyName* name,
                                                 BarrierKind barrier, TemporaryTypeSet* types);
-    MOZ_MUST_USE bool getPropTryUnboxed(bool* emitted, MDefinition* obj, PropertyName* name,
-                                        BarrierKind barrier, TemporaryTypeSet* types);
     MOZ_MUST_USE bool getPropTryCommonGetter(bool* emitted, MDefinition* obj, PropertyName* name,
                                              TemporaryTypeSet* types);
     MOZ_MUST_USE bool getPropTryInlineAccess(bool* emitted, MDefinition* obj, PropertyName* name,
@@ -475,9 +471,6 @@ class IonBuilder
     MOZ_MUST_USE bool setPropTryDefiniteSlot(bool* emitted, MDefinition* obj,
                                              PropertyName* name, MDefinition* value,
                                              bool barrier, TemporaryTypeSet* objTypes);
-    MOZ_MUST_USE bool setPropTryUnboxed(bool* emitted, MDefinition* obj,
-                                        PropertyName* name, MDefinition* value,
-                                        bool barrier, TemporaryTypeSet* objTypes);
     MOZ_MUST_USE bool setPropTryInlineAccess(bool* emitted, MDefinition* obj,
                                              PropertyName* name, MDefinition* value,
                                              bool barrier, TemporaryTypeSet* objTypes);
@@ -617,7 +610,6 @@ class IonBuilder
                                                         TypedObjectPrediction elemTypeReprs,
                                                         uint32_t elemSize);
     MOZ_MUST_USE bool initializeArrayElement(MDefinition* obj, size_t index, MDefinition* value,
-                                             JSValueType unboxedType,
                                              bool addResumePointAndIncrementInitializedLength);
 
     // jsop_getelem() helpers.
@@ -729,15 +721,13 @@ class IonBuilder
     MOZ_MUST_USE bool jsop_bindname(PropertyName* name);
     MOZ_MUST_USE bool jsop_bindvar();
     MOZ_MUST_USE bool jsop_getelem();
-    MOZ_MUST_USE bool jsop_getelem_dense(MDefinition* obj, MDefinition* index,
-                                         JSValueType unboxedType);
+    MOZ_MUST_USE bool jsop_getelem_dense(MDefinition* obj, MDefinition* index);
     MOZ_MUST_USE bool jsop_getelem_typed(MDefinition* obj, MDefinition* index,
                                          ScalarTypeDescr::Type arrayType);
     MOZ_MUST_USE bool jsop_setelem();
     MOZ_MUST_USE bool jsop_setelem_dense(TemporaryTypeSet::DoubleConversion conversion,
                                          MDefinition* object, MDefinition* index,
-                                         MDefinition* value, JSValueType unboxedType,
-                                         bool writeHole, bool* emitted);
+                                         MDefinition* value, bool writeHole, bool* emitted);
     MOZ_MUST_USE bool jsop_setelem_typed(ScalarTypeDescr::Type arrayType,
                                          MDefinition* object, MDefinition* index,
                                          MDefinition* value);
@@ -1041,7 +1031,6 @@ class IonBuilder
     MDefinition*
     addShapeGuardsForGetterSetter(MDefinition* obj, JSObject* holder, Shape* holderShape,
                                   const BaselineInspector::ReceiverVector& receivers,
-                                  const BaselineInspector::ObjectGroupVector& convertUnboxedGroups,
                                   bool isOwnProperty);
 
     MOZ_MUST_USE bool annotateGetPropertyCache(MDefinition* obj, PropertyName* name,
@@ -1059,22 +1048,6 @@ class IonBuilder
     ResultWithOOM<bool> testNotDefinedProperty(MDefinition* obj, jsid id);
 
     uint32_t getDefiniteSlot(TemporaryTypeSet* types, PropertyName* name, uint32_t* pnfixed);
-    MDefinition* convertUnboxedObjects(MDefinition* obj);
-    MDefinition* convertUnboxedObjects(MDefinition* obj,
-                                       const BaselineInspector::ObjectGroupVector& list);
-    uint32_t getUnboxedOffset(TemporaryTypeSet* types, PropertyName* name,
-                              JSValueType* punboxedType);
-    MInstruction* loadUnboxedProperty(MDefinition* obj, size_t offset, JSValueType unboxedType,
-                                      BarrierKind barrier, TemporaryTypeSet* types);
-    MInstruction* loadUnboxedValue(MDefinition* elements, size_t elementsOffset,
-                                   MDefinition* scaledOffset, JSValueType unboxedType,
-                                   BarrierKind barrier, TemporaryTypeSet* types);
-    MInstruction* storeUnboxedProperty(MDefinition* obj, size_t offset, JSValueType unboxedType,
-                                       MDefinition* value);
-    MInstruction* storeUnboxedValue(MDefinition* obj,
-                                    MDefinition* elements, int32_t elementsOffset,
-                                    MDefinition* scaledOffset, JSValueType unboxedType,
-                                    MDefinition* value, bool preBarrier = true);
     MOZ_MUST_USE bool checkPreliminaryGroups(MDefinition *obj);
     MOZ_MUST_USE bool freezePropTypeSets(TemporaryTypeSet* types,
                                          JSObject* foundProto, PropertyName* name);
diff --git a/js/src/jit/IonCaches.cpp b/js/src/jit/IonCaches.cpp
index 96e488ea8..9901bdd07 100644
--- a/js/src/jit/IonCaches.cpp
+++ b/js/src/jit/IonCaches.cpp
@@ -619,29 +619,7 @@ TestMatchingReceiver(MacroAssembler& masm, IonCache::StubAttacher& attacher,
                      Register object, JSObject* obj, Label* failure,
                      bool alwaysCheckGroup = false)
 {
-    if (obj->is<UnboxedPlainObject>()) {
-        MOZ_ASSERT(failure);
-
-        masm.branchTestObjGroup(Assembler::NotEqual, object, obj->group(), failure);
-        Address expandoAddress(object, UnboxedPlainObject::offsetOfExpando());
-        if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando()) {
-            masm.branchPtr(Assembler::Equal, expandoAddress, ImmWord(0), failure);
-            Label success;
-            masm.push(object);
-            masm.loadPtr(expandoAddress, object);
-            masm.branchTestObjShape(Assembler::Equal, object, expando->lastProperty(),
-                                    &success);
-            masm.pop(object);
-            masm.jump(failure);
-            masm.bind(&success);
-            masm.pop(object);
-        } else {
-            masm.branchPtr(Assembler::NotEqual, expandoAddress, ImmWord(0), failure);
-        }
-    } else if (obj->is<UnboxedArrayObject>()) {
-        MOZ_ASSERT(failure);
-        masm.branchTestObjGroup(Assembler::NotEqual, object, obj->group(), failure);
-    } else if (obj->is<TypedObject>()) {
+    if (obj->is<TypedObject>()) {
         attacher.branchNextStubOrLabel(masm, Assembler::NotEqual,
                                        Address(object, JSObject::offsetOfGroup()),
                                        ImmGCPtr(obj->group()), failure);
@@ -758,7 +736,6 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
     // jump directly. Otherwise, jump to the end of the stub, so there's a
     // common point to patch.
     bool multipleFailureJumps = (obj != holder)
-                             || obj->is<UnboxedPlainObject>()
                              || (checkTDZ && output.hasValue())
                              || (failures != nullptr && failures->used());
 
@@ -777,7 +754,6 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
     Register scratchReg = Register::FromCode(0); // Quell compiler warning.
 
     if (obj != holder ||
-        obj->is<UnboxedPlainObject>() ||
         !holder->as<NativeObject>().isFixedSlot(shape->slot()))
     {
         if (output.hasValue()) {
@@ -838,10 +814,6 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
 
             holderReg = InvalidReg;
         }
-    } else if (obj->is<UnboxedPlainObject>()) {
-        holder = obj->as<UnboxedPlainObject>().maybeExpando();
-        holderReg = scratchReg;
-        masm.loadPtr(Address(object, UnboxedPlainObject::offsetOfExpando()), holderReg);
     } else {
         holderReg = object;
     }
@@ -869,30 +841,6 @@ GenerateReadSlot(JSContext* cx, IonScript* ion, MacroAssembler& masm,
     attacher.jumpNextStub(masm);
 }
 
-static void
-GenerateReadUnboxed(JSContext* cx, IonScript* ion, MacroAssembler& masm,
-                    IonCache::StubAttacher& attacher, JSObject* obj,
-                    const UnboxedLayout::Property* property,
-                    Register object, TypedOrValueRegister output,
-                    Label* failures = nullptr)
-{
-    // Guard on the group of the object.
-    attacher.branchNextStubOrLabel(masm, Assembler::NotEqual,
-                                   Address(object, JSObject::offsetOfGroup()),
-                                   ImmGCPtr(obj->group()), failures);
-
-    Address address(object, UnboxedPlainObject::offsetOfData() + property->offset);
-
-    masm.loadUnboxedProperty(address, property->type, output);
-
-    attacher.jumpRejoin(masm);
-
-    if (failures) {
-        masm.bind(failures);
-        attacher.jumpNextStub(masm);
-    }
-}
-
 static bool
 EmitGetterCall(JSContext* cx, MacroAssembler& masm,
                IonCache::StubAttacher& attacher, JSObject* obj,
@@ -1187,39 +1135,6 @@ GenerateArrayLength(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher&
     return true;
 }
 
-static void
-GenerateUnboxedArrayLength(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& attacher,
-                           JSObject* array, Register object, TypedOrValueRegister output,
-                           Label* failures)
-{
-    Register outReg;
-    if (output.hasValue()) {
-        outReg = output.valueReg().scratchReg();
-    } else {
-        MOZ_ASSERT(output.type() == MIRType::Int32);
-        outReg = output.typedReg().gpr();
-    }
-    MOZ_ASSERT(object != outReg);
-
-    TestMatchingReceiver(masm, attacher, object, array, failures);
-
-    // Load length.
-    masm.load32(Address(object, UnboxedArrayObject::offsetOfLength()), outReg);
-
-    // Check for a length that fits in an int32.
-    masm.branchTest32(Assembler::Signed, outReg, outReg, failures);
-
-    if (output.hasValue())
-        masm.tagValue(JSVAL_TYPE_INT32, outReg, output.valueReg());
-
-    // Success.
-    attacher.jumpRejoin(masm);
-
-    // Failure.
-    masm.bind(failures);
-    attacher.jumpNextStub(masm);
-}
-
 // In this case, the code for TypedArray and SharedTypedArray is not the same,
 // because the code embeds pointers to the respective class arrays.  Code that
 // caches the stub code must distinguish between the two cases.
@@ -1533,101 +1448,6 @@ GetPropertyIC::tryAttachNative(JSContext* cx, HandleScript outerScript, IonScrip
 }
 
 bool
-GetPropertyIC::tryAttachUnboxed(JSContext* cx, HandleScript outerScript, IonScript* ion,
-                                HandleObject obj, HandleId id, void* returnAddr, bool* emitted)
-{
-    MOZ_ASSERT(canAttachStub());
-    MOZ_ASSERT(!*emitted);
-    MOZ_ASSERT(outerScript->ionScript() == ion);
-
-    if (!obj->is<UnboxedPlainObject>())
-        return true;
-    const UnboxedLayout::Property* property = obj->as<UnboxedPlainObject>().layout().lookup(id);
-    if (!property)
-        return true;
-
-    *emitted = true;
-
-    MacroAssembler masm(cx, ion, outerScript, profilerLeavePc_);
-
-    Label failures;
-    emitIdGuard(masm, id, &failures);
-    Label* maybeFailures = failures.used() ? &failures : nullptr;
-
-    StubAttacher attacher(*this);
-    GenerateReadUnboxed(cx, ion, masm, attacher, obj, property, object(), output(), maybeFailures);
-    return linkAndAttachStub(cx, masm, attacher, ion, "read unboxed",
-                             JS::TrackedOutcome::ICGetPropStub_UnboxedRead);
-}
-
-bool
-GetPropertyIC::tryAttachUnboxedExpando(JSContext* cx, HandleScript outerScript, IonScript* ion,
-                                       HandleObject obj, HandleId id, void* returnAddr, bool* emitted)
-{
-    MOZ_ASSERT(canAttachStub());
-    MOZ_ASSERT(!*emitted);
-    MOZ_ASSERT(outerScript->ionScript() == ion);
-
-    if (!obj->is<UnboxedPlainObject>())
-        return true;
-    Rooted<UnboxedExpandoObject*> expando(cx, obj->as<UnboxedPlainObject>().maybeExpando());
-    if (!expando)
-        return true;
-
-    Shape* shape = expando->lookup(cx, id);
-    if (!shape || !shape->hasDefaultGetter() || !shape->hasSlot())
-        return true;
-
-    *emitted = true;
-
-    MacroAssembler masm(cx, ion, outerScript, profilerLeavePc_);
-
-    Label failures;
-    emitIdGuard(masm, id, &failures);
-    Label* maybeFailures = failures.used() ? &failures : nullptr;
-
-    StubAttacher attacher(*this);
-    GenerateReadSlot(cx, ion, masm, attacher, DontCheckTDZ, obj, obj,
-                     shape, object(), output(), maybeFailures);
-    return linkAndAttachStub(cx, masm, attacher, ion, "read unboxed expando",
-                             JS::TrackedOutcome::ICGetPropStub_UnboxedReadExpando);
-}
-
-bool
-GetPropertyIC::tryAttachUnboxedArrayLength(JSContext* cx, HandleScript outerScript, IonScript* ion,
-                                           HandleObject obj, HandleId id, void* returnAddr,
-                                           bool* emitted)
-{
-    MOZ_ASSERT(canAttachStub());
-    MOZ_ASSERT(!*emitted);
-    MOZ_ASSERT(outerScript->ionScript() == ion);
-
-    if (!obj->is<UnboxedArrayObject>())
-        return true;
-
-    if (!JSID_IS_ATOM(id, cx->names().length))
-        return true;
-
-    if (obj->as<UnboxedArrayObject>().length() > INT32_MAX)
-        return true;
-
-    if (!allowArrayLength(cx))
-        return true;
-
-    *emitted = true;
-
-    MacroAssembler masm(cx, ion, outerScript, profilerLeavePc_);
-
-    Label failures;
-    emitIdGuard(masm, id, &failures);
-
-    StubAttacher attacher(*this);
-    GenerateUnboxedArrayLength(cx, masm, attacher, obj, object(), output(), &failures);
-    return linkAndAttachStub(cx, masm, attacher, ion, "unboxed array length",
-                             JS::TrackedOutcome::ICGetPropStub_UnboxedArrayLength);
-}
-
-bool
 GetPropertyIC::tryAttachTypedArrayLength(JSContext* cx, HandleScript outerScript, IonScript* ion,
                                          HandleObject obj, HandleId id, bool* emitted)
 {
@@ -2196,15 +2016,6 @@ GetPropertyIC::tryAttachStub(JSContext* cx, HandleScript outerScript, IonScript*
         if (!*emitted && !tryAttachNative(cx, outerScript, ion, obj, id, returnAddr, emitted))
             return false;
 
-        if (!*emitted && !tryAttachUnboxed(cx, outerScript, ion, obj, id, returnAddr, emitted))
-            return false;
-
-        if (!*emitted && !tryAttachUnboxedExpando(cx, outerScript, ion, obj, id, returnAddr, emitted))
-            return false;
-
-        if (!*emitted && !tryAttachUnboxedArrayLength(cx, outerScript, ion, obj, id, returnAddr, emitted))
-            return false;
-
         if (!*emitted && !tryAttachTypedArrayLength(cx, outerScript, ion, obj, id, emitted))
             return false;
     }
@@ -2383,12 +2194,6 @@ GenerateSetSlot(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& att
 
     NativeObject::slotsSizeMustNotOverflow();
 
-    if (obj->is<UnboxedPlainObject>()) {
-        obj = obj->as<UnboxedPlainObject>().maybeExpando();
-        masm.loadPtr(Address(object, UnboxedPlainObject::offsetOfExpando()), tempReg);
-        object = tempReg;
-    }
-
     if (obj->as<NativeObject>().isFixedSlot(shape->slot())) {
         Address addr(object, NativeObject::getFixedSlotOffset(shape->slot()));
 
@@ -3026,23 +2831,13 @@ GenerateAddSlot(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& att
     masm.branchTestObjGroup(Assembler::NotEqual, object, oldGroup, failures);
     if (obj->maybeShape()) {
         masm.branchTestObjShape(Assembler::NotEqual, object, oldShape, failures);
-    } else {
-        MOZ_ASSERT(obj->is<UnboxedPlainObject>());
-
-        Address expandoAddress(object, UnboxedPlainObject::offsetOfExpando());
-        masm.branchPtr(Assembler::Equal, expandoAddress, ImmWord(0), failures);
-
-        masm.loadPtr(expandoAddress, tempReg);
-        masm.branchTestObjShape(Assembler::NotEqual, tempReg, oldShape, failures);
     }
 
     Shape* newShape = obj->maybeShape();
-    if (!newShape)
-        newShape = obj->as<UnboxedPlainObject>().maybeExpando()->lastProperty();
 
     // Guard that the incoming value is in the type set for the property
     // if a type barrier is required.
-    if (checkTypeset)
+    if (newShape && checkTypeset)
         CheckTypeSetForWrite(masm, obj, newShape->propid(), tempReg, value, failures);
 
     // Guard shapes along prototype chain.
@@ -3063,9 +2858,7 @@ GenerateAddSlot(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& att
     }
 
     // Call a stub to (re)allocate dynamic slots, if necessary.
-    uint32_t newNumDynamicSlots = obj->is<UnboxedPlainObject>()
-                                  ? obj->as<UnboxedPlainObject>().maybeExpando()->numDynamicSlots()
-                                  : obj->as<NativeObject>().numDynamicSlots();
+    uint32_t newNumDynamicSlots = obj->as<NativeObject>().numDynamicSlots();
     if (NativeObject::dynamicSlotsCount(oldShape) != newNumDynamicSlots) {
         AllocatableRegisterSet regs(RegisterSet::Volatile());
         LiveRegisterSet save(regs.asLiveSet());
@@ -3076,12 +2869,6 @@ GenerateAddSlot(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& att
         Register temp1 = regs.takeAnyGeneral();
         Register temp2 = regs.takeAnyGeneral();
 
-        if (obj->is<UnboxedPlainObject>()) {
-            // Pass the expando object to the stub.
-            masm.Push(object);
-            masm.loadPtr(Address(object, UnboxedPlainObject::offsetOfExpando()), object);
-        }
-
         masm.setupUnalignedABICall(temp1);
         masm.loadJSContext(temp1);
         masm.passABIArg(temp1);
@@ -3098,27 +2885,16 @@ GenerateAddSlot(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& att
         masm.jump(&allocDone);
 
         masm.bind(&allocFailed);
-        if (obj->is<UnboxedPlainObject>())
-            masm.Pop(object);
         masm.PopRegsInMask(save);
         masm.jump(failures);
 
         masm.bind(&allocDone);
         masm.setFramePushed(framePushedAfterCall);
-        if (obj->is<UnboxedPlainObject>())
-            masm.Pop(object);
         masm.PopRegsInMask(save);
     }
 
     bool popObject = false;
 
-    if (obj->is<UnboxedPlainObject>()) {
-        masm.push(object);
-        popObject = true;
-        obj = obj->as<UnboxedPlainObject>().maybeExpando();
-        masm.loadPtr(Address(object, UnboxedPlainObject::offsetOfExpando()), object);
-    }
-
     // Write the object or expando object's new shape.
     Address shapeAddr(object, ShapedObject::offsetOfShape());
     if (cx->zone()->needsIncrementalBarrier())
@@ -3126,8 +2902,6 @@ GenerateAddSlot(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& att
     masm.storePtr(ImmGCPtr(newShape), shapeAddr);
 
     if (oldGroup != obj->group()) {
-        MOZ_ASSERT(!obj->is<UnboxedPlainObject>());
-
         // Changing object's group from a partially to fully initialized group,
         // per the acquired properties analysis. Only change the group if the
         // old group still has a newScript.
@@ -3370,141 +3144,6 @@ CanAttachNativeSetProp(JSContext* cx, HandleObject obj, HandleId id, const Const
     return SetPropertyIC::CanAttachNone;
 }
 
-static void
-GenerateSetUnboxed(JSContext* cx, MacroAssembler& masm, IonCache::StubAttacher& attacher,
-                   JSObject* obj, jsid id, uint32_t unboxedOffset, JSValueType unboxedType,
-                   Register object, Register tempReg, const ConstantOrRegister& value,
-                   bool checkTypeset, Label* failures)
-{
-    // Guard on the type of the object.
-    masm.branchPtr(Assembler::NotEqual,
-                   Address(object, JSObject::offsetOfGroup()),
-                   ImmGCPtr(obj->group()), failures);
-
-    if (checkTypeset)
-        CheckTypeSetForWrite(masm, obj, id, tempReg, value, failures);
-
-    Address address(object, UnboxedPlainObject::offsetOfData() + unboxedOffset);
-
-    if (cx->zone()->needsIncrementalBarrier()) {
-        if (unboxedType == JSVAL_TYPE_OBJECT)
-            masm.callPreBarrier(address, MIRType::Object);
-        else if (unboxedType == JSVAL_TYPE_STRING)
-            masm.callPreBarrier(address, MIRType::String);
-        else
-            MOZ_ASSERT(!UnboxedTypeNeedsPreBarrier(unboxedType));
-    }
-
-    masm.storeUnboxedProperty(address, unboxedType, value, failures);
-
-    attacher.jumpRejoin(masm);
-
-    masm.bind(failures);
-    attacher.jumpNextStub(masm);
-}
-
-static bool
-CanAttachSetUnboxed(JSContext* cx, HandleObject obj, HandleId id, const ConstantOrRegister& val,
-                    bool needsTypeBarrier, bool* checkTypeset,
-                    uint32_t* unboxedOffset, JSValueType* unboxedType)
-{
-    if (!obj->is<UnboxedPlainObject>())
-        return false;
-
-    const UnboxedLayout::Property* property = obj->as<UnboxedPlainObject>().layout().lookup(id);
-    if (property) {
-        *checkTypeset = false;
-        if (needsTypeBarrier && !CanInlineSetPropTypeCheck(obj, id, val, checkTypeset))
-            return false;
-        *unboxedOffset = property->offset;
-        *unboxedType = property->type;
-        return true;
-    }
-
-    return false;
-}
-
-static bool
-CanAttachSetUnboxedExpando(JSContext* cx, HandleObject obj, HandleId id,
-                           const ConstantOrRegister& val,
-                           bool needsTypeBarrier, bool* checkTypeset, Shape** pshape)
-{
-    if (!obj->is<UnboxedPlainObject>())
-        return false;
-
-    Rooted<UnboxedExpandoObject*> expando(cx, obj->as<UnboxedPlainObject>().maybeExpando());
-    if (!expando)
-        return false;
-
-    Shape* shape = expando->lookupPure(id);
-    if (!shape || !shape->hasDefaultSetter() || !shape->hasSlot() || !shape->writable())
-        return false;
-
-    *checkTypeset = false;
-    if (needsTypeBarrier && !CanInlineSetPropTypeCheck(obj, id, val, checkTypeset))
-        return false;
-
-    *pshape = shape;
-    return true;
-}
-
-static bool
-CanAttachAddUnboxedExpando(JSContext* cx, HandleObject obj, HandleShape oldShape,
-                           HandleId id, const ConstantOrRegister& val,
-                           bool needsTypeBarrier, bool* checkTypeset)
-{
-    if (!obj->is<UnboxedPlainObject>())
-        return false;
-
-    Rooted<UnboxedExpandoObject*> expando(cx, obj->as<UnboxedPlainObject>().maybeExpando());
-    if (!expando || expando->inDictionaryMode())
-        return false;
-
-    Shape* newShape = expando->lastProperty();
-    if (newShape->isEmptyShape() || newShape->propid() != id || newShape->previous() != oldShape)
-        return false;
-
-    MOZ_ASSERT(newShape->hasDefaultSetter() && newShape->hasSlot() && newShape->writable());
-
-    if (PrototypeChainShadowsPropertyAdd(cx, obj, id))
-        return false;
-
-    *checkTypeset = false;
-    if (needsTypeBarrier && !CanInlineSetPropTypeCheck(obj, id, val, checkTypeset))
-        return false;
-
-    return true;
-}
-
-bool
-SetPropertyIC::tryAttachUnboxed(JSContext* cx, HandleScript outerScript, IonScript* ion,
-                                HandleObject obj, HandleId id, bool* emitted)
-{
-    MOZ_ASSERT(!*emitted);
-
-    bool checkTypeset = false;
-    uint32_t unboxedOffset;
-    JSValueType unboxedType;
-    if (!CanAttachSetUnboxed(cx, obj, id, value(), needsTypeBarrier(), &checkTypeset,
-                             &unboxedOffset, &unboxedType))
-    {
-        return true;
-    }
-
-    *emitted = true;
-
-    MacroAssembler masm(cx, ion, outerScript, profilerLeavePc_);
-    StubAttacher attacher(*this);
-
-    Label failures;
-    emitIdGuard(masm, id, &failures);
-
-    GenerateSetUnboxed(cx, masm, attacher, obj, id, unboxedOffset, unboxedType,
-                       object(), temp(), value(), checkTypeset, &failures);
-    return linkAndAttachStub(cx, masm, attacher, ion, "set_unboxed",
-                             JS::TrackedOutcome::ICSetPropStub_SetUnboxed);
-}
-
 bool
 SetPropertyIC::tryAttachProxy(JSContext* cx, HandleScript outerScript, IonScript* ion,
                               HandleObject obj, HandleId id, bool* emitted)
@@ -3586,26 +3225,6 @@ SetPropertyIC::tryAttachNative(JSContext* cx, HandleScript outerScript, IonScrip
 }
 
 bool
-SetPropertyIC::tryAttachUnboxedExpando(JSContext* cx, HandleScript outerScript, IonScript* ion,
-                                       HandleObject obj, HandleId id, bool* emitted)
-{
-    MOZ_ASSERT(!*emitted);
-
-    RootedShape shape(cx);
-    bool checkTypeset = false;
-    if (!CanAttachSetUnboxedExpando(cx, obj, id, value(), needsTypeBarrier(),
-                                    &checkTypeset, shape.address()))
-    {
-        return true;
-    }
-
-    if (!attachSetSlot(cx, outerScript, ion, obj, shape, checkTypeset))
-        return false;
-    *emitted = true;
-    return true;
-}
-
-bool
 SetPropertyIC::tryAttachStub(JSContext* cx, HandleScript outerScript, IonScript* ion,
                              HandleObject obj, HandleValue idval, HandleValue value,
                              MutableHandleId id, bool* emitted, bool* tryNativeAddSlot)
@@ -3630,12 +3249,6 @@ SetPropertyIC::tryAttachStub(JSContext* cx, HandleScript outerScript, IonScript*
 
         if (!*emitted && !tryAttachNative(cx, outerScript, ion, obj, id, emitted, tryNativeAddSlot))
             return false;
-
-        if (!*emitted && !tryAttachUnboxed(cx, outerScript, ion, obj, id, emitted))
-            return false;
-
-        if (!*emitted && !tryAttachUnboxedExpando(cx, outerScript, ion, obj, id, emitted))
-            return false;
     }
 
     if (idval.isInt32()) {
@@ -3687,16 +3300,6 @@ SetPropertyIC::tryAttachAddSlot(JSContext* cx, HandleScript outerScript, IonScri
         return true;
     }
 
-    checkTypeset = false;
-    if (CanAttachAddUnboxedExpando(cx, obj, oldShape, id, value(), needsTypeBarrier(),
-                                   &checkTypeset))
-    {
-        if (!attachAddSlot(cx, outerScript, ion, obj, id, oldShape, oldGroup, checkTypeset))
-            return false;
-        *emitted = true;
-        return true;
-    }
-
     return true;
 }
 
@@ -3718,11 +3321,6 @@ SetPropertyIC::update(JSContext* cx, HandleScript outerScript, size_t cacheIndex
             return false;
 
         oldShape = obj->maybeShape();
-        if (obj->is<UnboxedPlainObject>()) {
-            MOZ_ASSERT(!oldShape);
-            if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando())
-                oldShape = expando->lastProperty();
-        }
     }
 
     RootedId id(cx);
@@ -4025,7 +3623,7 @@ GetPropertyIC::tryAttachDenseElementHole(JSContext* cx, HandleScript outerScript
 GetPropertyIC::canAttachTypedOrUnboxedArrayElement(JSObject* obj, const Value& idval,
                                                    TypedOrValueRegister output)
 {
-    if (!obj->is<TypedArrayObject>() && !obj->is<UnboxedArrayObject>())
+    if (!obj->is<TypedArrayObject>())
         return false;
 
     MOZ_ASSERT(idval.isInt32() || idval.isString());
@@ -4056,13 +3654,6 @@ GetPropertyIC::canAttachTypedOrUnboxedArrayElement(JSObject* obj, const Value& i
         return output.hasValue() || !output.typedReg().isFloat();
     }
 
-    if (index >= obj->as<UnboxedArrayObject>().initializedLength())
-        return false;
-
-    JSValueType elementType = obj->as<UnboxedArrayObject>().elementType();
-    if (elementType == JSVAL_TYPE_DOUBLE)
-        return output.hasValue();
-
     return output.hasValue() || !output.typedReg().isFloat();
 }
 
@@ -4139,46 +3730,27 @@ GenerateGetTypedOrUnboxedArrayElement(JSContext* cx, MacroAssembler& masm,
 
     Label popObjectAndFail;
 
-    if (array->is<TypedArrayObject>()) {
-        // Guard on the initialized length.
-        Address length(object, TypedArrayObject::lengthOffset());
-        masm.branch32(Assembler::BelowOrEqual, length, indexReg, &failures);
+    // Guard on the initialized length.
+    Address length(object, TypedArrayObject::lengthOffset());
+    masm.branch32(Assembler::BelowOrEqual, length, indexReg, &failures);
 
-        // Save the object register on the stack in case of failure.
-        Register elementReg = object;
-        masm.push(object);
+    // Save the object register on the stack in case of failure.
+    Register elementReg = object;
+    masm.push(object);
 
-        // Load elements vector.
-        masm.loadPtr(Address(object, TypedArrayObject::dataOffset()), elementReg);
+    // Load elements vector.
+    masm.loadPtr(Address(object, TypedArrayObject::dataOffset()), elementReg);
 
-        // Load the value. We use an invalid register because the destination
-        // register is necessary a non double register.
-        Scalar::Type arrayType = array->as<TypedArrayObject>().type();
-        int width = Scalar::byteSize(arrayType);
-        BaseIndex source(elementReg, indexReg, ScaleFromElemWidth(width));
-        if (output.hasValue()) {
-            masm.loadFromTypedArray(arrayType, source, output.valueReg(), allowDoubleResult,
-                                    elementReg, &popObjectAndFail);
-        } else {
-            masm.loadFromTypedArray(arrayType, source, output.typedReg(), elementReg, &popObjectAndFail);
-        }
+    // Load the value. We use an invalid register because the destination
+    // register is necessary a non double register.
+    Scalar::Type arrayType = array->as<TypedArrayObject>().type();
+    int width = Scalar::byteSize(arrayType);
+    BaseIndex source(elementReg, indexReg, ScaleFromElemWidth(width));
+    if (output.hasValue()) {
+        masm.loadFromTypedArray(arrayType, source, output.valueReg(), allowDoubleResult,
+                                elementReg, &popObjectAndFail);
     } else {
-        // Save the object register on the stack in case of failure.
-        masm.push(object);
-
-        // Guard on the initialized length.
-        masm.load32(Address(object, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()), object);
-        masm.and32(Imm32(UnboxedArrayObject::InitializedLengthMask), object);
-        masm.branch32(Assembler::BelowOrEqual, object, indexReg, &popObjectAndFail);
-
-        // Load elements vector.
-        Register elementReg = object;
-        masm.loadPtr(Address(masm.getStackPointer(), 0), object);
-        masm.loadPtr(Address(object, UnboxedArrayObject::offsetOfElements()), elementReg);
-
-        JSValueType elementType = array->as<UnboxedArrayObject>().elementType();
-        BaseIndex source(elementReg, indexReg, ScaleFromElemWidth(UnboxedTypeSize(elementType)));
-        masm.loadUnboxedProperty(source, elementType, output);
+        masm.loadFromTypedArray(arrayType, source, output.typedReg(), elementReg, &popObjectAndFail);
     }
 
     masm.pop(object);
diff --git a/js/src/jit/IonCaches.h b/js/src/jit/IonCaches.h
index 173e06c6b..b00646538 100644
--- a/js/src/jit/IonCaches.h
+++ b/js/src/jit/IonCaches.h
@@ -529,18 +529,6 @@ class GetPropertyIC : public IonCache
                                       HandleObject obj, HandleId id, void* returnAddr,
                                       bool* emitted);
 
-    MOZ_MUST_USE bool tryAttachUnboxed(JSContext* cx, HandleScript outerScript, IonScript* ion,
-                                       HandleObject obj, HandleId id, void* returnAddr,
-                                       bool* emitted);
-
-    MOZ_MUST_USE bool tryAttachUnboxedExpando(JSContext* cx, HandleScript outerScript,
-                                              IonScript* ion, HandleObject obj, HandleId id,
-                                              void* returnAddr, bool* emitted);
-
-    MOZ_MUST_USE bool tryAttachUnboxedArrayLength(JSContext* cx, HandleScript outerScript,
-                                                  IonScript* ion, HandleObject obj, HandleId id,
-                                                  void* returnAddr, bool* emitted);
-
     MOZ_MUST_USE bool tryAttachTypedArrayLength(JSContext* cx, HandleScript outerScript,
                                                 IonScript* ion, HandleObject obj, HandleId id,
                                                 bool* emitted);
diff --git a/js/src/jit/JitOptions.cpp b/js/src/jit/JitOptions.cpp
index b9a7c7b27..3f9d9db88 100644
--- a/js/src/jit/JitOptions.cpp
+++ b/js/src/jit/JitOptions.cpp
@@ -221,9 +221,6 @@ DefaultJitOptions::DefaultJitOptions()
             Warn(forcedRegisterAllocatorEnv, env);
     }
 
-    // Toggles whether unboxed plain objects can be created by the VM.
-    SET_DEFAULT(disableUnboxedObjects, true);
-
     // Test whether Atomics are allowed in asm.js code.
     SET_DEFAULT(asmJSAtomicsEnable, false);
 
diff --git a/js/src/jit/JitOptions.h b/js/src/jit/JitOptions.h
index 076980b4e..719ee14d9 100644
--- a/js/src/jit/JitOptions.h
+++ b/js/src/jit/JitOptions.h
@@ -91,9 +91,6 @@ struct DefaultJitOptions
     mozilla::Maybe<uint32_t> forcedDefaultIonSmallFunctionWarmUpThreshold;
     mozilla::Maybe<IonRegisterAllocator> forcedRegisterAllocator;
 
-    // The options below affect the rest of the VM, and not just the JIT.
-    bool disableUnboxedObjects;
-
     DefaultJitOptions();
     bool isSmallFunction(JSScript* script) const;
     void setEagerCompilation();
diff --git a/js/src/jit/Lowering.cpp b/js/src/jit/Lowering.cpp
index 709de9987..68417138b 100644
--- a/js/src/jit/Lowering.cpp
+++ b/js/src/jit/Lowering.cpp
@@ -2889,32 +2889,6 @@ LIRGenerator::visitSetInitializedLength(MSetInitializedLength* ins)
 }
 
 void
-LIRGenerator::visitUnboxedArrayLength(MUnboxedArrayLength* ins)
-{
-    define(new(alloc()) LUnboxedArrayLength(useRegisterAtStart(ins->object())), ins);
-}
-
-void
-LIRGenerator::visitUnboxedArrayInitializedLength(MUnboxedArrayInitializedLength* ins)
-{
-    define(new(alloc()) LUnboxedArrayInitializedLength(useRegisterAtStart(ins->object())), ins);
-}
-
-void
-LIRGenerator::visitIncrementUnboxedArrayInitializedLength(MIncrementUnboxedArrayInitializedLength* ins)
-{
-    add(new(alloc()) LIncrementUnboxedArrayInitializedLength(useRegister(ins->object())), ins);
-}
-
-void
-LIRGenerator::visitSetUnboxedArrayInitializedLength(MSetUnboxedArrayInitializedLength* ins)
-{
-    add(new(alloc()) LSetUnboxedArrayInitializedLength(useRegister(ins->object()),
-                                                       useRegisterOrConstant(ins->length()),
-                                                       temp()), ins);
-}
-
-void
 LIRGenerator::visitNot(MNot* ins)
 {
     MDefinition* op = ins->input();
@@ -3163,22 +3137,16 @@ LIRGenerator::visitStoreElementHole(MStoreElementHole* ins)
     const LUse elements = useRegister(ins->elements());
     const LAllocation index = useRegisterOrConstant(ins->index());
 
-    // Use a temp register when adding new elements to unboxed arrays.
-    LDefinition tempDef = LDefinition::BogusTemp();
-    if (ins->unboxedType() != JSVAL_TYPE_MAGIC)
-        tempDef = temp();
-
     LInstruction* lir;
     switch (ins->value()->type()) {
       case MIRType::Value:
-        lir = new(alloc()) LStoreElementHoleV(object, elements, index, useBox(ins->value()),
-                                              tempDef);
+        lir = new(alloc()) LStoreElementHoleV(object, elements, index, useBox(ins->value()));
         break;
 
       default:
       {
         const LAllocation value = useRegisterOrNonDoubleConstant(ins->value());
-        lir = new(alloc()) LStoreElementHoleT(object, elements, index, value, tempDef);
+        lir = new(alloc()) LStoreElementHoleT(object, elements, index, value);
         break;
       }
     }
@@ -3197,20 +3165,14 @@ LIRGenerator::visitFallibleStoreElement(MFallibleStoreElement* ins)
     const LUse elements = useRegister(ins->elements());
     const LAllocation index = useRegisterOrConstant(ins->index());
 
-    // Use a temp register when adding new elements to unboxed arrays.
-    LDefinition tempDef = LDefinition::BogusTemp();
-    if (ins->unboxedType() != JSVAL_TYPE_MAGIC)
-        tempDef = temp();
-
     LInstruction* lir;
     switch (ins->value()->type()) {
       case MIRType::Value:
-        lir = new(alloc()) LFallibleStoreElementV(object, elements, index, useBox(ins->value()),
-                                                  tempDef);
+        lir = new(alloc()) LFallibleStoreElementV(object, elements, index, useBox(ins->value()));
         break;
       default:
         const LAllocation value = useRegisterOrNonDoubleConstant(ins->value());
-        lir = new(alloc()) LFallibleStoreElementT(object, elements, index, value, tempDef);
+        lir = new(alloc()) LFallibleStoreElementT(object, elements, index, value);
         break;
     }
 
@@ -3252,14 +3214,6 @@ LIRGenerator::visitStoreUnboxedString(MStoreUnboxedString* ins)
 }
 
 void
-LIRGenerator::visitConvertUnboxedObjectToNative(MConvertUnboxedObjectToNative* ins)
-{
-    LInstruction* check = new(alloc()) LConvertUnboxedObjectToNative(useRegister(ins->object()));
-    add(check, ins);
-    assignSafepoint(check, ins);
-}
-
-void
 LIRGenerator::visitEffectiveAddress(MEffectiveAddress* ins)
 {
     define(new(alloc()) LEffectiveAddress(useRegister(ins->base()), useRegister(ins->index())), ins);
@@ -3777,24 +3731,6 @@ LIRGenerator::visitGuardReceiverPolymorphic(MGuardReceiverPolymorphic* ins)
 }
 
 void
-LIRGenerator::visitGuardUnboxedExpando(MGuardUnboxedExpando* ins)
-{
-    LGuardUnboxedExpando* guard =
-        new(alloc()) LGuardUnboxedExpando(useRegister(ins->object()));
-    assignSnapshot(guard, ins->bailoutKind());
-    add(guard, ins);
-    redefine(ins, ins->object());
-}
-
-void
-LIRGenerator::visitLoadUnboxedExpando(MLoadUnboxedExpando* ins)
-{
-    LLoadUnboxedExpando* lir =
-        new(alloc()) LLoadUnboxedExpando(useRegisterAtStart(ins->object()));
-    define(lir, ins);
-}
-
-void
 LIRGenerator::visitAssertRange(MAssertRange* ins)
 {
     MDefinition* input = ins->input();
diff --git a/js/src/jit/Lowering.h b/js/src/jit/Lowering.h
index 9b4095aec..b096bb143 100644
--- a/js/src/jit/Lowering.h
+++ b/js/src/jit/Lowering.h
@@ -216,10 +216,6 @@ class LIRGenerator : public LIRGeneratorSpecific
     void visitTypedObjectDescr(MTypedObjectDescr* ins);
     void visitInitializedLength(MInitializedLength* ins);
     void visitSetInitializedLength(MSetInitializedLength* ins);
-    void visitUnboxedArrayLength(MUnboxedArrayLength* ins);
-    void visitUnboxedArrayInitializedLength(MUnboxedArrayInitializedLength* ins);
-    void visitIncrementUnboxedArrayInitializedLength(MIncrementUnboxedArrayInitializedLength* ins);
-    void visitSetUnboxedArrayInitializedLength(MSetUnboxedArrayInitializedLength* ins);
     void visitNot(MNot* ins);
     void visitBoundsCheck(MBoundsCheck* ins);
     void visitBoundsCheckLower(MBoundsCheckLower* ins);
@@ -232,7 +228,6 @@ class LIRGenerator : public LIRGeneratorSpecific
     void visitFallibleStoreElement(MFallibleStoreElement* ins);
     void visitStoreUnboxedObjectOrNull(MStoreUnboxedObjectOrNull* ins);
     void visitStoreUnboxedString(MStoreUnboxedString* ins);
-    void visitConvertUnboxedObjectToNative(MConvertUnboxedObjectToNative* ins);
     void visitEffectiveAddress(MEffectiveAddress* ins);
     void visitArrayPopShift(MArrayPopShift* ins);
     void visitArrayPush(MArrayPush* ins);
@@ -256,8 +251,6 @@ class LIRGenerator : public LIRGeneratorSpecific
     void visitGuardObject(MGuardObject* ins);
     void visitGuardString(MGuardString* ins);
     void visitGuardReceiverPolymorphic(MGuardReceiverPolymorphic* ins);
-    void visitGuardUnboxedExpando(MGuardUnboxedExpando* ins);
-    void visitLoadUnboxedExpando(MLoadUnboxedExpando* ins);
     void visitPolyInlineGuard(MPolyInlineGuard* ins);
     void visitAssertRange(MAssertRange* ins);
     void visitCallGetProperty(MCallGetProperty* ins);
diff --git a/js/src/jit/MCallOptimize.cpp b/js/src/jit/MCallOptimize.cpp
index 01755094a..359f04639 100644
--- a/js/src/jit/MCallOptimize.cpp
+++ b/js/src/jit/MCallOptimize.cpp
@@ -30,7 +30,6 @@
 #include "jit/shared/Lowering-shared-inl.h"
 #include "vm/NativeObject-inl.h"
 #include "vm/StringObject-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using mozilla::ArrayLength;
 using mozilla::AssertedCast;
@@ -475,11 +474,6 @@ IonBuilder::inlineArray(CallInfo& callInfo)
         return InliningStatus_NotInlined;
     }
 
-    if (templateObject->is<UnboxedArrayObject>()) {
-        if (templateObject->group()->unboxedLayout().nativeGroup())
-            return InliningStatus_NotInlined;
-    }
-
     // Multiple arguments imply array initialization, not just construction.
     if (callInfo.argc() >= 2) {
         initLength = callInfo.argc();
@@ -527,7 +521,7 @@ IonBuilder::inlineArray(CallInfo& callInfo)
         // Make sure initLength matches the template object's length. This is
         // not guaranteed to be the case, for instance if we're inlining the
         // MConstant may come from an outer script.
-        if (initLength != GetAnyBoxedOrUnboxedArrayLength(templateObject))
+        if (initLength != templateObject->as<ArrayObject>().length())
             return InliningStatus_NotInlined;
 
         // Don't inline large allocations.
@@ -542,16 +536,15 @@ IonBuilder::inlineArray(CallInfo& callInfo)
 
     MDefinition* array = current->peek(-1);
     if (callInfo.argc() >= 2) {
-        JSValueType unboxedType = GetBoxedOrUnboxedType(templateObject);
         for (uint32_t i = 0; i < initLength; i++) {
             if (!alloc().ensureBallast())
                 return InliningStatus_Error;
             MDefinition* value = callInfo.getArg(i);
-            if (!initializeArrayElement(array, i, value, unboxedType, /* addResumePoint = */ false))
+            if (!initializeArrayElement(array, i, value, /* addResumePoint = */ false))
                 return InliningStatus_Error;
         }
 
-        MInstruction* setLength = setInitializedLength(array, unboxedType, initLength);
+        MInstruction* setLength = setInitializedLength(array, initLength);
         if (!resumeAfter(setLength))
             return InliningStatus_Error;
     }
@@ -584,7 +577,7 @@ IonBuilder::inlineArrayIsArray(CallInfo& callInfo)
         if (!clasp || clasp->isProxy())
             return InliningStatus_NotInlined;
 
-        isArray = (clasp == &ArrayObject::class_ || clasp == &UnboxedArrayObject::class_);
+        isArray = (clasp == &ArrayObject::class_);
     }
 
     pushConstant(BooleanValue(isArray));
@@ -615,34 +608,27 @@ IonBuilder::inlineArrayPopShift(CallInfo& callInfo, MArrayPopShift::Mode mode)
         OBJECT_FLAG_LENGTH_OVERFLOW |
         OBJECT_FLAG_ITERATED;
 
-    MDefinition* obj = convertUnboxedObjects(callInfo.thisArg());
+    MDefinition* obj = callInfo.thisArg();
     TemporaryTypeSet* thisTypes = obj->resultTypeSet();
     if (!thisTypes)
         return InliningStatus_NotInlined;
     const Class* clasp = thisTypes->getKnownClass(constraints());
-    if (clasp != &ArrayObject::class_ && clasp != &UnboxedArrayObject::class_)
+    if (clasp != &ArrayObject::class_)
         return InliningStatus_NotInlined;
     if (thisTypes->hasObjectFlags(constraints(), unhandledFlags)) {
         trackOptimizationOutcome(TrackedOutcome::ArrayBadFlags);
         return InliningStatus_NotInlined;
     }
 
-    if (ArrayPrototypeHasIndexedProperty(this, script())) {
+    // Watch out for extra indexed properties on the object or its prototype.
+    if (ElementAccessHasExtraIndexedProperty(this, obj)) {
         trackOptimizationOutcome(TrackedOutcome::ProtoIndexedProps);
         return InliningStatus_NotInlined;
     }
 
-    JSValueType unboxedType = JSVAL_TYPE_MAGIC;
-    if (clasp == &UnboxedArrayObject::class_) {
-        unboxedType = UnboxedArrayElementType(constraints(), obj, nullptr);
-        if (unboxedType == JSVAL_TYPE_MAGIC)
-            return InliningStatus_NotInlined;
-    }
-
     callInfo.setImplicitlyUsedUnchecked();
 
-    if (clasp == &ArrayObject::class_)
-        obj = addMaybeCopyElementsForWrite(obj, /* checkNative = */ false);
+    obj = addMaybeCopyElementsForWrite(obj, /* checkNative = */ false);
 
     TemporaryTypeSet* returnTypes = getInlineReturnTypeSet();
     bool needsHoleCheck = thisTypes->hasObjectFlags(constraints(), OBJECT_FLAG_NON_PACKED);
@@ -653,8 +639,7 @@ IonBuilder::inlineArrayPopShift(CallInfo& callInfo, MArrayPopShift::Mode mode)
     if (barrier != BarrierKind::NoBarrier)
         returnType = MIRType::Value;
 
-    MArrayPopShift* ins = MArrayPopShift::New(alloc(), obj, mode,
-                                              unboxedType, needsHoleCheck, maybeUndefined);
+    MArrayPopShift* ins = MArrayPopShift::New(alloc(), obj, mode, needsHoleCheck, maybeUndefined);
     current->add(ins);
     current->push(ins);
     ins->setResultType(returnType);
@@ -743,7 +728,7 @@ IonBuilder::inlineArrayPush(CallInfo& callInfo)
         return InliningStatus_NotInlined;
     }
 
-    MDefinition* obj = convertUnboxedObjects(callInfo.thisArg());
+    MDefinition* obj = callInfo.thisArg();
     MDefinition* value = callInfo.getArg(0);
     if (PropertyWriteNeedsTypeBarrier(alloc(), constraints(), current,
                                       &obj, nullptr, &value, /* canModify = */ false))
@@ -761,16 +746,10 @@ IonBuilder::inlineArrayPush(CallInfo& callInfo)
     if (!thisTypes)
         return InliningStatus_NotInlined;
     const Class* clasp = thisTypes->getKnownClass(constraints());
-    if (clasp != &ArrayObject::class_ && clasp != &UnboxedArrayObject::class_)
+    if (clasp != &ArrayObject::class_)
         return InliningStatus_NotInlined;
-    if (thisTypes->hasObjectFlags(constraints(), OBJECT_FLAG_SPARSE_INDEXES |
-                                  OBJECT_FLAG_LENGTH_OVERFLOW))
-    {
-        trackOptimizationOutcome(TrackedOutcome::ArrayBadFlags);
-        return InliningStatus_NotInlined;
-    }
 
-    if (ArrayPrototypeHasIndexedProperty(this, script())) {
+    if (ElementAccessHasExtraIndexedProperty(this, obj)) {
         trackOptimizationOutcome(TrackedOutcome::ProtoIndexedProps);
         return InliningStatus_NotInlined;
     }
@@ -782,13 +761,6 @@ IonBuilder::inlineArrayPush(CallInfo& callInfo)
         return InliningStatus_NotInlined;
     }
 
-    JSValueType unboxedType = JSVAL_TYPE_MAGIC;
-    if (clasp == &UnboxedArrayObject::class_) {
-        unboxedType = UnboxedArrayElementType(constraints(), obj, nullptr);
-        if (unboxedType == JSVAL_TYPE_MAGIC)
-            return InliningStatus_NotInlined;
-    }
-
     callInfo.setImplicitlyUsedUnchecked();
 
     if (conversion == TemporaryTypeSet::AlwaysConvertToDoubles ||
@@ -799,13 +771,12 @@ IonBuilder::inlineArrayPush(CallInfo& callInfo)
         value = valueDouble;
     }
 
-    if (unboxedType == JSVAL_TYPE_MAGIC)
-        obj = addMaybeCopyElementsForWrite(obj, /* checkNative = */ false);
+    obj = addMaybeCopyElementsForWrite(obj, /* checkNative = */ false);
 
     if (NeedsPostBarrier(value))
         current->add(MPostWriteBarrier::New(alloc(), obj, value));
 
-    MArrayPush* ins = MArrayPush::New(alloc(), obj, value, unboxedType);
+    MArrayPush* ins = MArrayPush::New(alloc(), obj, value);
     current->add(ins);
     current->push(ins);
 
@@ -822,7 +793,7 @@ IonBuilder::inlineArraySlice(CallInfo& callInfo)
         return InliningStatus_NotInlined;
     }
 
-    MDefinition* obj = convertUnboxedObjects(callInfo.thisArg());
+    MDefinition* obj = callInfo.thisArg();
 
     // Ensure |this| and result are objects.
     if (getInlineReturnType() != MIRType::Object)
@@ -846,24 +817,11 @@ IonBuilder::inlineArraySlice(CallInfo& callInfo)
         return InliningStatus_NotInlined;
 
     const Class* clasp = thisTypes->getKnownClass(constraints());
-    if (clasp != &ArrayObject::class_ && clasp != &UnboxedArrayObject::class_)
-        return InliningStatus_NotInlined;
-    if (thisTypes->hasObjectFlags(constraints(), OBJECT_FLAG_SPARSE_INDEXES |
-                                  OBJECT_FLAG_LENGTH_OVERFLOW))
-    {
-        trackOptimizationOutcome(TrackedOutcome::ArrayBadFlags);
+    if (clasp != &ArrayObject::class_)
         return InliningStatus_NotInlined;
-    }
-
-    JSValueType unboxedType = JSVAL_TYPE_MAGIC;
-    if (clasp == &UnboxedArrayObject::class_) {
-        unboxedType = UnboxedArrayElementType(constraints(), obj, nullptr);
-        if (unboxedType == JSVAL_TYPE_MAGIC)
-            return InliningStatus_NotInlined;
-    }
 
-    // Watch out for indexed properties on the prototype.
-    if (ArrayPrototypeHasIndexedProperty(this, script())) {
+    // Watch out for indexed properties on the object or its prototype.
+    if (ElementAccessHasExtraIndexedProperty(this, obj)) {
         trackOptimizationOutcome(TrackedOutcome::ProtoIndexedProps);
         return InliningStatus_NotInlined;
     }
@@ -882,15 +840,8 @@ IonBuilder::inlineArraySlice(CallInfo& callInfo)
     if (!templateObj)
         return InliningStatus_NotInlined;
 
-    if (unboxedType == JSVAL_TYPE_MAGIC) {
-        if (!templateObj->is<ArrayObject>())
-            return InliningStatus_NotInlined;
-    } else {
-        if (!templateObj->is<UnboxedArrayObject>())
-            return InliningStatus_NotInlined;
-        if (templateObj->as<UnboxedArrayObject>().elementType() != unboxedType)
-            return InliningStatus_NotInlined;
-    }
+    if (!templateObj->is<ArrayObject>())
+        return InliningStatus_NotInlined;
 
     callInfo.setImplicitlyUsedUnchecked();
 
@@ -909,16 +860,12 @@ IonBuilder::inlineArraySlice(CallInfo& callInfo)
 
         end = MArrayLength::New(alloc(), elements);
         current->add(end->toInstruction());
-    } else {
-        end = MUnboxedArrayLength::New(alloc(), obj);
-        current->add(end->toInstruction());
     }
 
     MArraySlice* ins = MArraySlice::New(alloc(), constraints(),
                                         obj, begin, end,
                                         templateObj,
-                                        templateObj->group()->initialHeap(constraints()),
-                                        unboxedType);
+                                        templateObj->group()->initialHeap(constraints()));
     current->add(ins);
     current->push(ins);
 
@@ -1437,7 +1384,7 @@ IonBuilder::inlineConstantStringSplitString(CallInfo& callInfo)
     // Check if exist a template object in stub.
     JSString* stringStr = nullptr;
     JSString* stringSep = nullptr;
-    JSObject* templateObject = nullptr;
+    ArrayObject* templateObject = nullptr;
     if (!inspector->isOptimizableCallStringSplit(pc, &stringStr, &stringSep, &templateObject))
         return InliningStatus_NotInlined;
 
@@ -1463,13 +1410,13 @@ IonBuilder::inlineConstantStringSplitString(CallInfo& callInfo)
     if (!key.maybeTypes()->hasType(TypeSet::StringType()))
         return InliningStatus_NotInlined;
 
-    uint32_t initLength = GetAnyBoxedOrUnboxedArrayLength(templateObject);
-    if (GetAnyBoxedOrUnboxedInitializedLength(templateObject) != initLength)
+    uint32_t initLength = templateObject->length();
+    if (templateObject->getDenseInitializedLength() != initLength)
         return InliningStatus_NotInlined;
 
     Vector<MConstant*, 0, SystemAllocPolicy> arrayValues;
     for (uint32_t i = 0; i < initLength; i++) {
-        Value str = GetAnyBoxedOrUnboxedDenseElement(templateObject, i);
+        Value str = templateObject->getDenseElement(i);
         MOZ_ASSERT(str.toString()->isAtom());
         MConstant* value = MConstant::New(alloc().fallible(), str, constraints());
         if (!value)
@@ -1500,8 +1447,6 @@ IonBuilder::inlineConstantStringSplitString(CallInfo& callInfo)
         return InliningStatus_Inlined;
     }
 
-    JSValueType unboxedType = GetBoxedOrUnboxedType(templateObject);
-
     // Store all values, no need to initialize the length after each as
     // jsop_initelem_array is doing because we do not expect to bailout
     // because the memory is supposed to be allocated by now.
@@ -1512,11 +1457,11 @@ IonBuilder::inlineConstantStringSplitString(CallInfo& callInfo)
         MConstant* value = arrayValues[i];
         current->add(value);
 
-        if (!initializeArrayElement(array, i, value, unboxedType, /* addResumePoint = */ false))
+        if (!initializeArrayElement(array, i, value, /* addResumePoint = */ false))
             return InliningStatus_Error;
     }
 
-    MInstruction* setLength = setInitializedLength(array, unboxedType, initLength);
+    MInstruction* setLength = setInitializedLength(array, initLength);
     if (!resumeAfter(setLength))
         return InliningStatus_Error;
 
@@ -2152,7 +2097,7 @@ IonBuilder::inlineDefineDataProperty(CallInfo& callInfo)
     if (callInfo.argc() != 3)
         return InliningStatus_NotInlined;
 
-    MDefinition* obj = convertUnboxedObjects(callInfo.getArg(0));
+    MDefinition* obj = callInfo.getArg(0);
     MDefinition* id = callInfo.getArg(1);
     MDefinition* value = callInfo.getArg(2);
 
diff --git a/js/src/jit/MIR.cpp b/js/src/jit/MIR.cpp
index 287b87582..fa9cc3019 100644
--- a/js/src/jit/MIR.cpp
+++ b/js/src/jit/MIR.cpp
@@ -4810,67 +4810,31 @@ MBeta::printOpcode(GenericPrinter& out) const
 bool
 MCreateThisWithTemplate::canRecoverOnBailout() const
 {
-    MOZ_ASSERT(templateObject()->is<PlainObject>() || templateObject()->is<UnboxedPlainObject>());
-    MOZ_ASSERT_IF(templateObject()->is<PlainObject>(),
-                  !templateObject()->as<PlainObject>().denseElementsAreCopyOnWrite());
-    return true;
-}
-
-bool
-OperandIndexMap::init(TempAllocator& alloc, JSObject* templateObject)
-{
-    const UnboxedLayout& layout =
-        templateObject->as<UnboxedPlainObject>().layoutDontCheckGeneration();
-
-    const UnboxedLayout::PropertyVector& properties = layout.properties();
-    MOZ_ASSERT(properties.length() < 255);
-
-    // Allocate an array of indexes, where the top of each field correspond to
-    // the index of the operand in the MObjectState instance.
-    if (!map.init(alloc, layout.size()))
-        return false;
-
-    // Reset all indexes to 0, which is an error code.
-    for (size_t i = 0; i < map.length(); i++)
-        map[i] = 0;
-
-    // Map the property offsets to the indexes of MObjectState operands.
-    uint8_t index = 1;
-    for (size_t i = 0; i < properties.length(); i++, index++)
-        map[properties[i].offset] = index;
-
+    MOZ_ASSERT(templateObject()->is<PlainObject>());
+    MOZ_ASSERT(!templateObject()->as<PlainObject>().denseElementsAreCopyOnWrite());
     return true;
 }
 
 MObjectState::MObjectState(MObjectState* state)
   : numSlots_(state->numSlots_),
-    numFixedSlots_(state->numFixedSlots_),
-    operandIndex_(state->operandIndex_)
+    numFixedSlots_(state->numFixedSlots_)
 {
     // This instruction is only used as a summary for bailout paths.
     setResultType(MIRType::Object);
     setRecoveredOnBailout();
 }
 
-MObjectState::MObjectState(JSObject *templateObject, OperandIndexMap* operandIndex)
+MObjectState::MObjectState(JSObject* templateObject)
 {
     // This instruction is only used as a summary for bailout paths.
     setResultType(MIRType::Object);
     setRecoveredOnBailout();
 
-    if (templateObject->is<NativeObject>()) {
-        NativeObject* nativeObject = &templateObject->as<NativeObject>();
-        numSlots_ = nativeObject->slotSpan();
-        numFixedSlots_ = nativeObject->numFixedSlots();
-    } else {
-        const UnboxedLayout& layout =
-            templateObject->as<UnboxedPlainObject>().layoutDontCheckGeneration();
-        // Same as UnboxedLayout::makeNativeGroup
-        numSlots_ = layout.properties().length();
-        numFixedSlots_ = gc::GetGCKindSlots(layout.getAllocKind());
-    }
+    MOZ_ASSERT(templateObject->is<NativeObject>());
 
-    operandIndex_ = operandIndex;
+    NativeObject* nativeObject = &templateObject->as<NativeObject>();
+    numSlots_ = nativeObject->slotSpan();
+    numFixedSlots_ = nativeObject->numFixedSlots();
 }
 
 JSObject*
@@ -4905,39 +4869,21 @@ MObjectState::initFromTemplateObject(TempAllocator& alloc, MDefinition* undefine
     // the template object. This is needed to account values which are baked in
     // the template objects and not visible in IonMonkey, such as the
     // uninitialized-lexical magic value of call objects.
-    if (templateObject->is<UnboxedPlainObject>()) {
-        UnboxedPlainObject& unboxedObject = templateObject->as<UnboxedPlainObject>();
-        const UnboxedLayout& layout = unboxedObject.layoutDontCheckGeneration();
-        const UnboxedLayout::PropertyVector& properties = layout.properties();
-
-        for (size_t i = 0; i < properties.length(); i++) {
-            Value val = unboxedObject.getValue(properties[i], /* maybeUninitialized = */ true);
-            MDefinition *def = undefinedVal;
-            if (!val.isUndefined()) {
-                MConstant* ins = val.isObject() ?
-                    MConstant::NewConstraintlessObject(alloc, &val.toObject()) :
-                    MConstant::New(alloc, val);
-                block()->insertBefore(this, ins);
-                def = ins;
-            }
-            initSlot(i, def);
-        }
-    } else {
-        NativeObject& nativeObject = templateObject->as<NativeObject>();
-        MOZ_ASSERT(nativeObject.slotSpan() == numSlots());
-
-        for (size_t i = 0; i < numSlots(); i++) {
-            Value val = nativeObject.getSlot(i);
-            MDefinition *def = undefinedVal;
-            if (!val.isUndefined()) {
-                MConstant* ins = val.isObject() ?
-                    MConstant::NewConstraintlessObject(alloc, &val.toObject()) :
-                    MConstant::New(alloc, val);
-                block()->insertBefore(this, ins);
-                def = ins;
-            }
-            initSlot(i, def);
+    NativeObject& nativeObject = templateObject->as<NativeObject>();
+    MOZ_ASSERT(nativeObject.slotSpan() == numSlots());
+
+	MOZ_ASSERT(templateObject->is<NativeObject>());
+    for (size_t i = 0; i < numSlots(); i++) {
+        Value val = nativeObject.getSlot(i);
+        MDefinition *def = undefinedVal;
+        if (!val.isUndefined()) {
+            MConstant* ins = val.isObject() ?
+                MConstant::NewConstraintlessObject(alloc, &val.toObject()) :
+                MConstant::New(alloc, val);
+            block()->insertBefore(this, ins);
+            def = ins;
         }
+        initSlot(i, def);
     }
     return true;
 }
@@ -4948,14 +4894,7 @@ MObjectState::New(TempAllocator& alloc, MDefinition* obj)
     JSObject* templateObject = templateObjectOf(obj);
     MOZ_ASSERT(templateObject, "Unexpected object creation.");
 
-    OperandIndexMap* operandIndex = nullptr;
-    if (templateObject->is<UnboxedPlainObject>()) {
-        operandIndex = new(alloc) OperandIndexMap;
-        if (!operandIndex || !operandIndex->init(alloc, templateObject))
-            return nullptr;
-    }
-
-    MObjectState* res = new(alloc) MObjectState(templateObject, operandIndex);
+    MObjectState* res = new(alloc) MObjectState(templateObject);
     if (!res || !res->init(alloc, obj))
         return nullptr;
     return res;
@@ -5862,35 +5801,6 @@ MGetFirstDollarIndex::foldsTo(TempAllocator& alloc)
     return MConstant::New(alloc, Int32Value(index));
 }
 
-MConvertUnboxedObjectToNative*
-MConvertUnboxedObjectToNative::New(TempAllocator& alloc, MDefinition* obj, ObjectGroup* group)
-{
-    MConvertUnboxedObjectToNative* res = new(alloc) MConvertUnboxedObjectToNative(obj, group);
-
-    ObjectGroup* nativeGroup = group->unboxedLayout().nativeGroup();
-
-    // Make a new type set for the result of this instruction which replaces
-    // the input group with the native group we will convert it to.
-    TemporaryTypeSet* types = obj->resultTypeSet();
-    if (types && !types->unknownObject()) {
-        TemporaryTypeSet* newTypes = types->cloneWithoutObjects(alloc.lifoAlloc());
-        if (newTypes) {
-            for (size_t i = 0; i < types->getObjectCount(); i++) {
-                TypeSet::ObjectKey* key = types->getObject(i);
-                if (!key)
-                    continue;
-                if (key->unknownProperties() || !key->isGroup() || key->group() != group)
-                    newTypes->addType(TypeSet::ObjectType(key), alloc.lifoAlloc());
-                else
-                    newTypes->addType(TypeSet::ObjectType(nativeGroup), alloc.lifoAlloc());
-            }
-            res->setResultTypeSet(newTypes);
-        }
-    }
-
-    return res;
-}
-
 bool
 jit::ElementAccessIsDenseNative(CompilerConstraintList* constraints,
                                 MDefinition* obj, MDefinition* id)
@@ -5910,48 +5820,6 @@ jit::ElementAccessIsDenseNative(CompilerConstraintList* constraints,
     return clasp && clasp->isNative() && !IsTypedArrayClass(clasp);
 }
 
-JSValueType
-jit::UnboxedArrayElementType(CompilerConstraintList* constraints, MDefinition* obj,
-                             MDefinition* id)
-{
-    if (obj->mightBeType(MIRType::String))
-        return JSVAL_TYPE_MAGIC;
-
-    if (id && id->type() != MIRType::Int32 && id->type() != MIRType::Double)
-        return JSVAL_TYPE_MAGIC;
-
-    TemporaryTypeSet* types = obj->resultTypeSet();
-    if (!types || types->unknownObject())
-        return JSVAL_TYPE_MAGIC;
-
-    JSValueType elementType = JSVAL_TYPE_MAGIC;
-    for (unsigned i = 0; i < types->getObjectCount(); i++) {
-        TypeSet::ObjectKey* key = types->getObject(i);
-        if (!key)
-            continue;
-
-        if (key->unknownProperties() || !key->isGroup())
-            return JSVAL_TYPE_MAGIC;
-
-        if (key->clasp() != &UnboxedArrayObject::class_)
-            return JSVAL_TYPE_MAGIC;
-
-        const UnboxedLayout &layout = key->group()->unboxedLayout();
-
-        if (layout.nativeGroup())
-            return JSVAL_TYPE_MAGIC;
-
-        if (elementType == layout.elementType() || elementType == JSVAL_TYPE_MAGIC)
-            elementType = layout.elementType();
-        else
-            return JSVAL_TYPE_MAGIC;
-
-        key->watchStateChangeForUnboxedConvertedToNative(constraints);
-    }
-
-    return elementType;
-}
-
 bool
 jit::ElementAccessIsTypedArray(CompilerConstraintList* constraints,
                                MDefinition* obj, MDefinition* id,
@@ -6111,11 +5979,6 @@ ObjectSubsumes(TypeSet::ObjectKey* first, TypeSet::ObjectKey* second)
                firstElements.maybeTypes()->equals(secondElements.maybeTypes());
     }
 
-    if (first->clasp() == &UnboxedArrayObject::class_) {
-        return first->group()->unboxedLayout().elementType() ==
-               second->group()->unboxedLayout().elementType();
-    }
-
     return false;
 }
 
@@ -6355,15 +6218,6 @@ PrototypeHasIndexedProperty(IonBuilder* builder, JSObject* obj)
     return false;
 }
 
-// Whether Array.prototype, or an object on its proto chain, has an indexed property.
-bool
-jit::ArrayPrototypeHasIndexedProperty(IonBuilder* builder, JSScript* script)
-{
-    if (JSObject* proto = script->global().maybeGetArrayPrototype())
-        return PrototypeHasIndexedProperty(builder, proto);
-    return true;
-}
-
 // Whether obj or any of its prototypes have an indexed property.
 bool
 jit::TypeCanHaveExtraIndexedProperties(IonBuilder* builder, TemporaryTypeSet* types)
@@ -6579,23 +6433,6 @@ jit::PropertyWriteNeedsTypeBarrier(TempAllocator& alloc, CompilerConstraintList*
         }
     }
 
-    // Perform additional filtering to make sure that any unboxed property
-    // being written can accommodate the value.
-    for (size_t i = 0; i < types->getObjectCount(); i++) {
-        TypeSet::ObjectKey* key = types->getObject(i);
-        if (key && key->isGroup() && key->group()->maybeUnboxedLayout()) {
-            const UnboxedLayout& layout = key->group()->unboxedLayout();
-            if (name) {
-                const UnboxedLayout::Property* property = layout.lookup(name);
-                if (property && !CanStoreUnboxedType(alloc, property->type, *pvalue))
-                    return true;
-            } else {
-                if (layout.isArray() && !CanStoreUnboxedType(alloc, layout.elementType(), *pvalue))
-                    return true;
-            }
-        }
-    }
-
     if (success)
         return false;
 
@@ -6626,17 +6463,6 @@ jit::PropertyWriteNeedsTypeBarrier(TempAllocator& alloc, CompilerConstraintList*
 
     MOZ_ASSERT(excluded);
 
-    // If the excluded object is a group with an unboxed layout, make sure it
-    // does not have a corresponding native group. Objects with the native
-    // group might appear even though they are not in the type set.
-    if (excluded->isGroup()) {
-        if (UnboxedLayout* layout = excluded->group()->maybeUnboxedLayout()) {
-            if (layout->nativeGroup())
-                return true;
-            excluded->watchStateChangeForUnboxedConvertedToNative(constraints);
-        }
-    }
-
     *pobj = AddGroupGuard(alloc, current, *pobj, excluded, /* bailOnEquality = */ true);
     return false;
 }
diff --git a/js/src/jit/MIR.h b/js/src/jit/MIR.h
index fb0f22fc3..0992768bf 100644
--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -30,7 +30,6 @@
 #include "vm/EnvironmentObject.h"
 #include "vm/SharedMem.h"
 #include "vm/TypedArrayCommon.h"
-#include "vm/UnboxedObject.h"
 
 // Undo windows.h damage on Win64
 #undef MemoryBarrier
@@ -376,8 +375,7 @@ class AliasSet {
         Element           = 1 << 1, // A Value member of obj->elements or
                                     // a typed object.
         UnboxedElement    = 1 << 2, // An unboxed scalar or reference member of
-                                    // a typed array, typed object, or unboxed
-                                    // object.
+                                    // typed object.
         DynamicSlot       = 1 << 3, // A Value member of obj->slots.
         FixedSlot         = 1 << 4, // A Value member of obj->fixedSlots().
         DOMProperty       = 1 << 5, // A DOM property
@@ -434,9 +432,6 @@ class AliasSet {
         MOZ_ASSERT(flags && !(flags & Store_));
         return AliasSet(flags | Store_);
     }
-    static uint32_t BoxedOrUnboxedElements(JSValueType type) {
-        return (type == JSVAL_TYPE_MAGIC) ? Element : UnboxedElement;
-    }
 };
 
 typedef Vector<MDefinition*, 6, JitAllocPolicy> MDefinitionVector;
@@ -3763,14 +3758,9 @@ class MObjectState
 {
   private:
     uint32_t numSlots_;
-    uint32_t numFixedSlots_;        // valid if isUnboxed() == false.
-    OperandIndexMap* operandIndex_; // valid if isUnboxed() == true.
-
-    bool isUnboxed() const {
-        return operandIndex_ != nullptr;
-    }
+    uint32_t numFixedSlots_;
 
-    MObjectState(JSObject *templateObject, OperandIndexMap* operandIndex);
+    MObjectState(JSObject *templateObject);
     explicit MObjectState(MObjectState* state);
 
     MOZ_MUST_USE bool init(TempAllocator& alloc, MDefinition* obj);
@@ -3831,18 +3821,6 @@ class MObjectState
         setSlot(slot + numFixedSlots(), def);
     }
 
-    // Interface reserved for unboxed objects.
-    bool hasOffset(uint32_t offset) const {
-        MOZ_ASSERT(isUnboxed());
-        return offset < operandIndex_->map.length() && operandIndex_->map[offset] != 0;
-    }
-    MDefinition* getOffset(uint32_t offset) const {
-        return getOperand(operandIndex_->map[offset]);
-    }
-    void setOffset(uint32_t offset, MDefinition* def) {
-        replaceOperand(operandIndex_->map[offset], def);
-    }
-
     MOZ_MUST_USE bool writeRecoverData(CompactBufferWriter& writer) const override;
     bool canRecoverOnBailout() const override {
         return true;
@@ -8746,102 +8724,6 @@ class MSetInitializedLength
     ALLOW_CLONE(MSetInitializedLength)
 };
 
-// Load the length from an unboxed array.
-class MUnboxedArrayLength
-  : public MUnaryInstruction,
-    public SingleObjectPolicy::Data
-{
-    explicit MUnboxedArrayLength(MDefinition* object)
-      : MUnaryInstruction(object)
-    {
-        setResultType(MIRType::Int32);
-        setMovable();
-    }
-
-  public:
-    INSTRUCTION_HEADER(UnboxedArrayLength)
-    TRIVIAL_NEW_WRAPPERS
-    NAMED_OPERANDS((0, object))
-
-    bool congruentTo(const MDefinition* ins) const override {
-        return congruentIfOperandsEqual(ins);
-    }
-    AliasSet getAliasSet() const override {
-        return AliasSet::Load(AliasSet::ObjectFields);
-    }
-
-    ALLOW_CLONE(MUnboxedArrayLength)
-};
-
-// Load the initialized length from an unboxed array.
-class MUnboxedArrayInitializedLength
-  : public MUnaryInstruction,
-    public SingleObjectPolicy::Data
-{
-    explicit MUnboxedArrayInitializedLength(MDefinition* object)
-      : MUnaryInstruction(object)
-    {
-        setResultType(MIRType::Int32);
-        setMovable();
-    }
-
-  public:
-    INSTRUCTION_HEADER(UnboxedArrayInitializedLength)
-    TRIVIAL_NEW_WRAPPERS
-    NAMED_OPERANDS((0, object))
-
-    bool congruentTo(const MDefinition* ins) const override {
-        return congruentIfOperandsEqual(ins);
-    }
-    AliasSet getAliasSet() const override {
-        return AliasSet::Load(AliasSet::ObjectFields);
-    }
-
-    ALLOW_CLONE(MUnboxedArrayInitializedLength)
-};
-
-// Increment the initialized length of an unboxed array object.
-class MIncrementUnboxedArrayInitializedLength
-  : public MUnaryInstruction,
-    public SingleObjectPolicy::Data
-{
-    explicit MIncrementUnboxedArrayInitializedLength(MDefinition* obj)
-      : MUnaryInstruction(obj)
-    {}
-
-  public:
-    INSTRUCTION_HEADER(IncrementUnboxedArrayInitializedLength)
-    TRIVIAL_NEW_WRAPPERS
-    NAMED_OPERANDS((0, object))
-
-    AliasSet getAliasSet() const override {
-        return AliasSet::Store(AliasSet::ObjectFields);
-    }
-
-    ALLOW_CLONE(MIncrementUnboxedArrayInitializedLength)
-};
-
-// Set the initialized length of an unboxed array object.
-class MSetUnboxedArrayInitializedLength
-  : public MBinaryInstruction,
-    public SingleObjectPolicy::Data
-{
-    explicit MSetUnboxedArrayInitializedLength(MDefinition* obj, MDefinition* length)
-      : MBinaryInstruction(obj, length)
-    {}
-
-  public:
-    INSTRUCTION_HEADER(SetUnboxedArrayInitializedLength)
-    TRIVIAL_NEW_WRAPPERS
-    NAMED_OPERANDS((0, object), (1, length))
-
-    AliasSet getAliasSet() const override {
-        return AliasSet::Store(AliasSet::ObjectFields);
-    }
-
-    ALLOW_CLONE(MSetUnboxedArrayInitializedLength)
-};
-
 // Load the array length from an elements header.
 class MArrayLength
   : public MUnaryInstruction,
@@ -9335,23 +9217,19 @@ class MLoadElement
     ALLOW_CLONE(MLoadElement)
 };
 
-// Load a value from the elements vector for a dense native or unboxed array.
+// Load a value from the elements vector of a native object.
 // If the index is out-of-bounds, or the indexed slot has a hole, undefined is
 // returned instead.
 class MLoadElementHole
   : public MTernaryInstruction,
     public SingleObjectPolicy::Data
 {
-    // Unboxed element type, JSVAL_TYPE_MAGIC for dense native elements.
-    JSValueType unboxedType_;
-
     bool needsNegativeIntCheck_;
     bool needsHoleCheck_;
 
     MLoadElementHole(MDefinition* elements, MDefinition* index, MDefinition* initLength,
-                     JSValueType unboxedType, bool needsHoleCheck)
+                     bool needsHoleCheck)
       : MTernaryInstruction(elements, index, initLength),
-        unboxedType_(unboxedType),
         needsNegativeIntCheck_(true),
         needsHoleCheck_(needsHoleCheck)
     {
@@ -9373,9 +9251,6 @@ class MLoadElementHole
     TRIVIAL_NEW_WRAPPERS
     NAMED_OPERANDS((0, elements), (1, index), (2, initLength))
 
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
     bool needsNegativeIntCheck() const {
         return needsNegativeIntCheck_;
     }
@@ -9386,8 +9261,6 @@ class MLoadElementHole
         if (!ins->isLoadElementHole())
             return false;
         const MLoadElementHole* other = ins->toLoadElementHole();
-        if (unboxedType() != other->unboxedType())
-            return false;
         if (needsHoleCheck() != other->needsHoleCheck())
             return false;
         if (needsNegativeIntCheck() != other->needsNegativeIntCheck())
@@ -9395,7 +9268,7 @@ class MLoadElementHole
         return congruentIfOperandsEqual(other);
     }
     AliasSet getAliasSet() const override {
-        return AliasSet::Load(AliasSet::BoxedOrUnboxedElements(unboxedType()));
+        return AliasSet::Load(AliasSet::Element);
     }
     void collectRangeInfoPreTrunc() override;
 
@@ -9575,20 +9448,17 @@ class MStoreElement
     ALLOW_CLONE(MStoreElement)
 };
 
-// Like MStoreElement, but supports indexes >= initialized length, and can
-// handle unboxed arrays. The downside is that we cannot hoist the elements
-// vector and bounds check, since this instruction may update the (initialized)
-// length and reallocate the elements vector.
+// Like MStoreElement, but supports indexes >= initialized length. The downside
+// is that we cannot hoist the elements vector and bounds check, since this
+// instruction may update the (initialized) length and reallocate the elements
+// vector.
 class MStoreElementHole
   : public MAryInstruction<4>,
     public MStoreElementCommon,
     public MixPolicy<SingleObjectPolicy, NoFloatPolicy<3> >::Data
 {
-    JSValueType unboxedType_;
-
     MStoreElementHole(MDefinition* object, MDefinition* elements,
-                      MDefinition* index, MDefinition* value, JSValueType unboxedType)
-      : unboxedType_(unboxedType)
+                      MDefinition* index, MDefinition* value)
     {
         initOperand(0, object);
         initOperand(1, elements);
@@ -9603,14 +9473,10 @@ class MStoreElementHole
     TRIVIAL_NEW_WRAPPERS
     NAMED_OPERANDS((0, object), (1, elements), (2, index), (3, value))
 
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
     AliasSet getAliasSet() const override {
         // StoreElementHole can update the initialized length, the array length
         // or reallocate obj->elements.
-        return AliasSet::Store(AliasSet::ObjectFields |
-                               AliasSet::BoxedOrUnboxedElements(unboxedType()));
+        return AliasSet::Store(AliasSet::ObjectFields | AliasSet::Element);
     }
 
     ALLOW_CLONE(MStoreElementHole)
@@ -9623,13 +9489,11 @@ class MFallibleStoreElement
     public MStoreElementCommon,
     public MixPolicy<SingleObjectPolicy, NoFloatPolicy<3> >::Data
 {
-    JSValueType unboxedType_;
     bool strict_;
 
     MFallibleStoreElement(MDefinition* object, MDefinition* elements,
                           MDefinition* index, MDefinition* value,
-                          JSValueType unboxedType, bool strict)
-      : unboxedType_(unboxedType)
+                          bool strict)
     {
         initOperand(0, object);
         initOperand(1, elements);
@@ -9645,12 +9509,8 @@ class MFallibleStoreElement
     TRIVIAL_NEW_WRAPPERS
     NAMED_OPERANDS((0, object), (1, elements), (2, index), (3, value))
 
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
     AliasSet getAliasSet() const override {
-        return AliasSet::Store(AliasSet::ObjectFields |
-                               AliasSet::BoxedOrUnboxedElements(unboxedType()));
+        return AliasSet::Store(AliasSet::ObjectFields | AliasSet::Element);
     }
     bool strict() const {
         return strict_;
@@ -9742,59 +9602,6 @@ class MStoreUnboxedString
     ALLOW_CLONE(MStoreUnboxedString)
 };
 
-// Passes through an object, after ensuring it is converted from an unboxed
-// object to a native representation.
-class MConvertUnboxedObjectToNative
-  : public MUnaryInstruction,
-    public SingleObjectPolicy::Data
-{
-    CompilerObjectGroup group_;
-
-    explicit MConvertUnboxedObjectToNative(MDefinition* obj, ObjectGroup* group)
-      : MUnaryInstruction(obj),
-        group_(group)
-    {
-        setGuard();
-        setMovable();
-        setResultType(MIRType::Object);
-    }
-
-  public:
-    INSTRUCTION_HEADER(ConvertUnboxedObjectToNative)
-    NAMED_OPERANDS((0, object))
-
-    static MConvertUnboxedObjectToNative* New(TempAllocator& alloc, MDefinition* obj,
-                                              ObjectGroup* group);
-
-    ObjectGroup* group() const {
-        return group_;
-    }
-    bool congruentTo(const MDefinition* ins) const override {
-        if (!congruentIfOperandsEqual(ins))
-            return false;
-        return ins->toConvertUnboxedObjectToNative()->group() == group();
-    }
-    AliasSet getAliasSet() const override {
-        // This instruction can read and write to all parts of the object, but
-        // is marked as non-effectful so it can be consolidated by LICM and GVN
-        // and avoid inhibiting other optimizations.
-        //
-        // This is valid to do because when unboxed objects might have a native
-        // group they can be converted to, we do not optimize accesses to the
-        // unboxed objects and do not guard on their group or shape (other than
-        // in this opcode).
-        //
-        // Later accesses can assume the object has a native representation
-        // and optimize accordingly. Those accesses cannot be reordered before
-        // this instruction, however. This is prevented by chaining this
-        // instruction with the object itself, in the same way as MBoundsCheck.
-        return AliasSet::None();
-    }
-    bool appendRoots(MRootList& roots) const override {
-        return roots.append(group_);
-    }
-};
-
 // Array.prototype.pop or Array.prototype.shift on a dense array.
 class MArrayPopShift
   : public MUnaryInstruction,
@@ -9808,13 +9615,12 @@ class MArrayPopShift
 
   private:
     Mode mode_;
-    JSValueType unboxedType_;
     bool needsHoleCheck_;
     bool maybeUndefined_;
 
-    MArrayPopShift(MDefinition* object, Mode mode, JSValueType unboxedType,
+    MArrayPopShift(MDefinition* object, Mode mode,
                    bool needsHoleCheck, bool maybeUndefined)
-      : MUnaryInstruction(object), mode_(mode), unboxedType_(unboxedType),
+      : MUnaryInstruction(object), mode_(mode),
         needsHoleCheck_(needsHoleCheck), maybeUndefined_(maybeUndefined)
     { }
 
@@ -9832,12 +9638,8 @@ class MArrayPopShift
     bool mode() const {
         return mode_;
     }
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
     AliasSet getAliasSet() const override {
-        return AliasSet::Store(AliasSet::ObjectFields |
-                               AliasSet::BoxedOrUnboxedElements(unboxedType()));
+        return AliasSet::Store(AliasSet::ObjectFields | AliasSet::Element);
     }
 
     ALLOW_CLONE(MArrayPopShift)
@@ -9848,10 +9650,8 @@ class MArrayPush
   : public MBinaryInstruction,
     public MixPolicy<SingleObjectPolicy, NoFloatPolicy<1> >::Data
 {
-    JSValueType unboxedType_;
-
-    MArrayPush(MDefinition* object, MDefinition* value, JSValueType unboxedType)
-      : MBinaryInstruction(object, value), unboxedType_(unboxedType)
+    MArrayPush(MDefinition* object, MDefinition* value)
+      : MBinaryInstruction(object, value)
     {
         setResultType(MIRType::Int32);
     }
@@ -9861,12 +9661,8 @@ class MArrayPush
     TRIVIAL_NEW_WRAPPERS
     NAMED_OPERANDS((0, object), (1, value))
 
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
     AliasSet getAliasSet() const override {
-        return AliasSet::Store(AliasSet::ObjectFields |
-                               AliasSet::BoxedOrUnboxedElements(unboxedType()));
+        return AliasSet::Store(AliasSet::ObjectFields | AliasSet::Element);
     }
     void computeRange(TempAllocator& alloc) override;
 
@@ -9880,15 +9676,13 @@ class MArraySlice
 {
     CompilerObject templateObj_;
     gc::InitialHeap initialHeap_;
-    JSValueType unboxedType_;
 
     MArraySlice(CompilerConstraintList* constraints, MDefinition* obj,
                 MDefinition* begin, MDefinition* end,
-                JSObject* templateObj, gc::InitialHeap initialHeap, JSValueType unboxedType)
+                JSObject* templateObj, gc::InitialHeap initialHeap)
       : MTernaryInstruction(obj, begin, end),
         templateObj_(templateObj),
-        initialHeap_(initialHeap),
-        unboxedType_(unboxedType)
+        initialHeap_(initialHeap)
     {
         setResultType(MIRType::Object);
     }
@@ -9906,10 +9700,6 @@ class MArraySlice
         return initialHeap_;
     }
 
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
-
     bool possiblyCalls() const override {
         return true;
     }
@@ -11174,11 +10964,6 @@ class MGuardShape
         setMovable();
         setResultType(MIRType::Object);
         setResultTypeSet(obj->resultTypeSet());
-
-        // Disallow guarding on unboxed object shapes. The group is better to
-        // guard on, and guarding on the shape can interact badly with
-        // MConvertUnboxedObjectToNative.
-        MOZ_ASSERT(shape->getObjectClass() != &UnboxedPlainObject::class_);
     }
 
   public:
@@ -11273,11 +11058,6 @@ class MGuardObjectGroup
         setGuard();
         setMovable();
         setResultType(MIRType::Object);
-
-        // Unboxed groups which might be converted to natives can't be guarded
-        // on, due to MConvertUnboxedObjectToNative.
-        MOZ_ASSERT_IF(group->maybeUnboxedLayoutDontCheckGeneration(),
-                      !group->unboxedLayoutDontCheckGeneration().nativeGroup());
     }
 
   public:
@@ -11386,73 +11166,6 @@ class MGuardClass
     ALLOW_CLONE(MGuardClass)
 };
 
-// Guard on the presence or absence of an unboxed object's expando.
-class MGuardUnboxedExpando
-  : public MUnaryInstruction,
-    public SingleObjectPolicy::Data
-{
-    bool requireExpando_;
-    BailoutKind bailoutKind_;
-
-    MGuardUnboxedExpando(MDefinition* obj, bool requireExpando, BailoutKind bailoutKind)
-      : MUnaryInstruction(obj),
-        requireExpando_(requireExpando),
-        bailoutKind_(bailoutKind)
-    {
-        setGuard();
-        setMovable();
-        setResultType(MIRType::Object);
-    }
-
-  public:
-    INSTRUCTION_HEADER(GuardUnboxedExpando)
-    TRIVIAL_NEW_WRAPPERS
-    NAMED_OPERANDS((0, object))
-
-    bool requireExpando() const {
-        return requireExpando_;
-    }
-    BailoutKind bailoutKind() const {
-        return bailoutKind_;
-    }
-    bool congruentTo(const MDefinition* ins) const override {
-        if (!congruentIfOperandsEqual(ins))
-            return false;
-        if (requireExpando() != ins->toGuardUnboxedExpando()->requireExpando())
-            return false;
-        return true;
-    }
-    AliasSet getAliasSet() const override {
-        return AliasSet::Load(AliasSet::ObjectFields);
-    }
-};
-
-// Load an unboxed plain object's expando.
-class MLoadUnboxedExpando
-  : public MUnaryInstruction,
-    public SingleObjectPolicy::Data
-{
-  private:
-    explicit MLoadUnboxedExpando(MDefinition* object)
-      : MUnaryInstruction(object)
-    {
-        setResultType(MIRType::Object);
-        setMovable();
-    }
-
-  public:
-    INSTRUCTION_HEADER(LoadUnboxedExpando)
-    TRIVIAL_NEW_WRAPPERS
-    NAMED_OPERANDS((0, object))
-
-    bool congruentTo(const MDefinition* ins) const override {
-        return congruentIfOperandsEqual(ins);
-    }
-    AliasSet getAliasSet() const override {
-        return AliasSet::Load(AliasSet::ObjectFields);
-    }
-};
-
 // Load from vp[slot] (slots that are not inline in an object).
 class MLoadSlot
   : public MUnaryInstruction,
@@ -12355,15 +12068,13 @@ class MInArray
 {
     bool needsHoleCheck_;
     bool needsNegativeIntCheck_;
-    JSValueType unboxedType_;
 
     MInArray(MDefinition* elements, MDefinition* index,
              MDefinition* initLength, MDefinition* object,
-             bool needsHoleCheck, JSValueType unboxedType)
+             bool needsHoleCheck)
       : MQuaternaryInstruction(elements, index, initLength, object),
         needsHoleCheck_(needsHoleCheck),
-        needsNegativeIntCheck_(true),
-        unboxedType_(unboxedType)
+        needsNegativeIntCheck_(true)
     {
         setResultType(MIRType::Boolean);
         setMovable();
@@ -12383,9 +12094,6 @@ class MInArray
     bool needsNegativeIntCheck() const {
         return needsNegativeIntCheck_;
     }
-    JSValueType unboxedType() const {
-        return unboxedType_;
-    }
     void collectRangeInfoPreTrunc() override;
     AliasSet getAliasSet() const override {
         return AliasSet::Load(AliasSet::Element);
@@ -12398,8 +12106,6 @@ class MInArray
             return false;
         if (needsNegativeIntCheck() != other->needsNegativeIntCheck())
             return false;
-        if (unboxedType() != other->unboxedType())
-            return false;
         return congruentIfOperandsEqual(other);
     }
 };
@@ -14300,8 +14006,6 @@ MDefinition::maybeConstantValue()
 
 bool ElementAccessIsDenseNative(CompilerConstraintList* constraints,
                                 MDefinition* obj, MDefinition* id);
-JSValueType UnboxedArrayElementType(CompilerConstraintList* constraints, MDefinition* obj,
-                                    MDefinition* id);
 bool ElementAccessIsTypedArray(CompilerConstraintList* constraints,
                                MDefinition* obj, MDefinition* id,
                                Scalar::Type* arrayType);
@@ -14333,7 +14037,6 @@ bool PropertyWriteNeedsTypeBarrier(TempAllocator& alloc, CompilerConstraintList*
                                    MBasicBlock* current, MDefinition** pobj,
                                    PropertyName* name, MDefinition** pvalue,
                                    bool canModify, MIRType implicitType = MIRType::None);
-bool ArrayPrototypeHasIndexedProperty(IonBuilder* builder, JSScript* script);
 bool TypeCanHaveExtraIndexedProperties(IonBuilder* builder, TemporaryTypeSet* types);
 
 inline MIRType
diff --git a/js/src/jit/MOpcodes.h b/js/src/jit/MOpcodes.h
index fddc1e637..ab37604b4 100644
--- a/js/src/jit/MOpcodes.h
+++ b/js/src/jit/MOpcodes.h
@@ -187,8 +187,6 @@ namespace jit {
     _(GuardObjectGroup)                                                     \
     _(GuardObjectIdentity)                                                  \
     _(GuardClass)                                                           \
-    _(GuardUnboxedExpando)                                                  \
-    _(LoadUnboxedExpando)                                                   \
     _(ArrayLength)                                                          \
     _(SetArrayLength)                                                       \
     _(GetNextEntryForIterator)                                              \
@@ -200,10 +198,6 @@ namespace jit {
     _(SetTypedObjectOffset)                                                 \
     _(InitializedLength)                                                    \
     _(SetInitializedLength)                                                 \
-    _(UnboxedArrayLength)                                                   \
-    _(UnboxedArrayInitializedLength)                                        \
-    _(IncrementUnboxedArrayInitializedLength)                               \
-    _(SetUnboxedArrayInitializedLength)                                     \
     _(Not)                                                                  \
     _(BoundsCheck)                                                          \
     _(BoundsCheckLower)                                                     \
@@ -219,7 +213,6 @@ namespace jit {
     _(StoreUnboxedScalar)                                                   \
     _(StoreUnboxedObjectOrNull)                                             \
     _(StoreUnboxedString)                                                   \
-    _(ConvertUnboxedObjectToNative)                                         \
     _(ArrayPopShift)                                                        \
     _(ArrayPush)                                                            \
     _(ArraySlice)                                                           \
diff --git a/js/src/jit/MacroAssembler.cpp b/js/src/jit/MacroAssembler.cpp
index f633b9b7b..a739b9325 100644
--- a/js/src/jit/MacroAssembler.cpp
+++ b/js/src/jit/MacroAssembler.cpp
@@ -126,20 +126,14 @@ MacroAssembler::guardTypeSetMightBeIncomplete(TypeSet* types, Register obj, Regi
 {
     // Type set guards might miss when an object's group changes. In this case
     // either its old group's properties will become unknown, or it will change
-    // to a native object with an original unboxed group. Jump to label if this
-    // might have happened for the input object.
+    // to a native object. Jump to label if this might have happened for the
+    // input object.
 
     if (types->unknownObject()) {
         jump(label);
         return;
     }
 
-    loadPtr(Address(obj, JSObject::offsetOfGroup()), scratch);
-    load32(Address(scratch, ObjectGroup::offsetOfFlags()), scratch);
-    and32(Imm32(OBJECT_FLAG_ADDENDUM_MASK), scratch);
-    branch32(Assembler::Equal,
-             scratch, Imm32(ObjectGroup::addendumOriginalUnboxedGroupValue()), label);
-
     for (size_t i = 0; i < types->getObjectCount(); i++) {
         if (JSObject* singleton = types->getSingletonNoBarrier(i)) {
             movePtr(ImmGCPtr(singleton), scratch);
@@ -468,268 +462,6 @@ template void MacroAssembler::loadFromTypedArray(Scalar::Type arrayType, const A
 template void MacroAssembler::loadFromTypedArray(Scalar::Type arrayType, const BaseIndex& src, const ValueOperand& dest,
                                                  bool allowDouble, Register temp, Label* fail);
 
-template <typename T>
-void
-MacroAssembler::loadUnboxedProperty(T address, JSValueType type, TypedOrValueRegister output)
-{
-    switch (type) {
-      case JSVAL_TYPE_INT32: {
-          // Handle loading an int32 into a double reg.
-          if (output.type() == MIRType::Double) {
-              convertInt32ToDouble(address, output.typedReg().fpu());
-              break;
-          }
-          MOZ_FALLTHROUGH;
-      }
-
-      case JSVAL_TYPE_BOOLEAN:
-      case JSVAL_TYPE_STRING: {
-        Register outReg;
-        if (output.hasValue()) {
-            outReg = output.valueReg().scratchReg();
-        } else {
-            MOZ_ASSERT(output.type() == MIRTypeFromValueType(type));
-            outReg = output.typedReg().gpr();
-        }
-
-        switch (type) {
-          case JSVAL_TYPE_BOOLEAN:
-            load8ZeroExtend(address, outReg);
-            break;
-          case JSVAL_TYPE_INT32:
-            load32(address, outReg);
-            break;
-          case JSVAL_TYPE_STRING:
-            loadPtr(address, outReg);
-            break;
-          default:
-            MOZ_CRASH();
-        }
-
-        if (output.hasValue())
-            tagValue(type, outReg, output.valueReg());
-        break;
-      }
-
-      case JSVAL_TYPE_OBJECT:
-        if (output.hasValue()) {
-            Register scratch = output.valueReg().scratchReg();
-            loadPtr(address, scratch);
-
-            Label notNull, done;
-            branchPtr(Assembler::NotEqual, scratch, ImmWord(0), &notNull);
-
-            moveValue(NullValue(), output.valueReg());
-            jump(&done);
-
-            bind(&notNull);
-            tagValue(JSVAL_TYPE_OBJECT, scratch, output.valueReg());
-
-            bind(&done);
-        } else {
-            // Reading null can't be possible here, as otherwise the result
-            // would be a value (either because null has been read before or
-            // because there is a barrier).
-            Register reg = output.typedReg().gpr();
-            loadPtr(address, reg);
-#ifdef DEBUG
-            Label ok;
-            branchTestPtr(Assembler::NonZero, reg, reg, &ok);
-            assumeUnreachable("Null not possible");
-            bind(&ok);
-#endif
-        }
-        break;
-
-      case JSVAL_TYPE_DOUBLE:
-        // Note: doubles in unboxed objects are not accessed through other
-        // views and do not need canonicalization.
-        if (output.hasValue())
-            loadValue(address, output.valueReg());
-        else
-            loadDouble(address, output.typedReg().fpu());
-        break;
-
-      default:
-        MOZ_CRASH();
-    }
-}
-
-template void
-MacroAssembler::loadUnboxedProperty(Address address, JSValueType type,
-                                    TypedOrValueRegister output);
-
-template void
-MacroAssembler::loadUnboxedProperty(BaseIndex address, JSValueType type,
-                                    TypedOrValueRegister output);
-
-static void
-StoreUnboxedFailure(MacroAssembler& masm, Label* failure)
-{
-    // Storing a value to an unboxed property is a fallible operation and
-    // the caller must provide a failure label if a particular unboxed store
-    // might fail. Sometimes, however, a store that cannot succeed (such as
-    // storing a string to an int32 property) will be marked as infallible.
-    // This can only happen if the code involved is unreachable.
-    if (failure)
-        masm.jump(failure);
-    else
-        masm.assumeUnreachable("Incompatible write to unboxed property");
-}
-
-template <typename T>
-void
-MacroAssembler::storeUnboxedProperty(T address, JSValueType type,
-                                     const ConstantOrRegister& value, Label* failure)
-{
-    switch (type) {
-      case JSVAL_TYPE_BOOLEAN:
-        if (value.constant()) {
-            if (value.value().isBoolean())
-                store8(Imm32(value.value().toBoolean()), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else if (value.reg().hasTyped()) {
-            if (value.reg().type() == MIRType::Boolean)
-                store8(value.reg().typedReg().gpr(), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else {
-            if (failure)
-                branchTestBoolean(Assembler::NotEqual, value.reg().valueReg(), failure);
-            storeUnboxedPayload(value.reg().valueReg(), address, /* width = */ 1);
-        }
-        break;
-
-      case JSVAL_TYPE_INT32:
-        if (value.constant()) {
-            if (value.value().isInt32())
-                store32(Imm32(value.value().toInt32()), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else if (value.reg().hasTyped()) {
-            if (value.reg().type() == MIRType::Int32)
-                store32(value.reg().typedReg().gpr(), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else {
-            if (failure)
-                branchTestInt32(Assembler::NotEqual, value.reg().valueReg(), failure);
-            storeUnboxedPayload(value.reg().valueReg(), address, /* width = */ 4);
-        }
-        break;
-
-      case JSVAL_TYPE_DOUBLE:
-        if (value.constant()) {
-            if (value.value().isNumber()) {
-                loadConstantDouble(value.value().toNumber(), ScratchDoubleReg);
-                storeDouble(ScratchDoubleReg, address);
-            } else {
-                StoreUnboxedFailure(*this, failure);
-            }
-        } else if (value.reg().hasTyped()) {
-            if (value.reg().type() == MIRType::Int32) {
-                convertInt32ToDouble(value.reg().typedReg().gpr(), ScratchDoubleReg);
-                storeDouble(ScratchDoubleReg, address);
-            } else if (value.reg().type() == MIRType::Double) {
-                storeDouble(value.reg().typedReg().fpu(), address);
-            } else {
-                StoreUnboxedFailure(*this, failure);
-            }
-        } else {
-            ValueOperand reg = value.reg().valueReg();
-            Label notInt32, end;
-            branchTestInt32(Assembler::NotEqual, reg, &notInt32);
-            int32ValueToDouble(reg, ScratchDoubleReg);
-            storeDouble(ScratchDoubleReg, address);
-            jump(&end);
-            bind(&notInt32);
-            if (failure)
-                branchTestDouble(Assembler::NotEqual, reg, failure);
-            storeValue(reg, address);
-            bind(&end);
-        }
-        break;
-
-      case JSVAL_TYPE_OBJECT:
-        if (value.constant()) {
-            if (value.value().isObjectOrNull())
-                storePtr(ImmGCPtr(value.value().toObjectOrNull()), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else if (value.reg().hasTyped()) {
-            MOZ_ASSERT(value.reg().type() != MIRType::Null);
-            if (value.reg().type() == MIRType::Object)
-                storePtr(value.reg().typedReg().gpr(), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else {
-            if (failure) {
-                Label ok;
-                branchTestNull(Assembler::Equal, value.reg().valueReg(), &ok);
-                branchTestObject(Assembler::NotEqual, value.reg().valueReg(), failure);
-                bind(&ok);
-            }
-            storeUnboxedPayload(value.reg().valueReg(), address, /* width = */ sizeof(uintptr_t));
-        }
-        break;
-
-      case JSVAL_TYPE_STRING:
-        if (value.constant()) {
-            if (value.value().isString())
-                storePtr(ImmGCPtr(value.value().toString()), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else if (value.reg().hasTyped()) {
-            if (value.reg().type() == MIRType::String)
-                storePtr(value.reg().typedReg().gpr(), address);
-            else
-                StoreUnboxedFailure(*this, failure);
-        } else {
-            if (failure)
-                branchTestString(Assembler::NotEqual, value.reg().valueReg(), failure);
-            storeUnboxedPayload(value.reg().valueReg(), address, /* width = */ sizeof(uintptr_t));
-        }
-        break;
-
-      default:
-        MOZ_CRASH();
-    }
-}
-
-template void
-MacroAssembler::storeUnboxedProperty(Address address, JSValueType type,
-                                     const ConstantOrRegister& value, Label* failure);
-
-template void
-MacroAssembler::storeUnboxedProperty(BaseIndex address, JSValueType type,
-                                     const ConstantOrRegister& value, Label* failure);
-
-void
-MacroAssembler::checkUnboxedArrayCapacity(Register obj, const RegisterOrInt32Constant& index,
-                                          Register temp, Label* failure)
-{
-    Address initLengthAddr(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength());
-    Address lengthAddr(obj, UnboxedArrayObject::offsetOfLength());
-
-    Label capacityIsIndex, done;
-    load32(initLengthAddr, temp);
-    branchTest32(Assembler::NonZero, temp, Imm32(UnboxedArrayObject::CapacityMask), &capacityIsIndex);
-    branch32(Assembler::BelowOrEqual, lengthAddr, index, failure);
-    jump(&done);
-    bind(&capacityIsIndex);
-
-    // Do a partial shift so that we can get an absolute offset from the base
-    // of CapacityArray to use.
-    JS_STATIC_ASSERT(sizeof(UnboxedArrayObject::CapacityArray[0]) == 4);
-    rshiftPtr(Imm32(UnboxedArrayObject::CapacityShift - 2), temp);
-    and32(Imm32(~0x3), temp);
-
-    addPtr(ImmPtr(&UnboxedArrayObject::CapacityArray), temp);
-    branch32(Assembler::BelowOrEqual, Address(temp, 0), index, failure);
-    bind(&done);
-}
-
 // Inlined version of gc::CheckAllocatorState that checks the bare essentials
 // and bails for anything that cannot be handled with our jit allocators.
 void
@@ -1277,20 +1009,6 @@ MacroAssembler::initGCThing(Register obj, Register temp, JSObject* templateObj,
             nbytes = (nbytes < sizeof(uintptr_t)) ? 0 : nbytes - sizeof(uintptr_t);
             offset += sizeof(uintptr_t);
         }
-    } else if (templateObj->is<UnboxedPlainObject>()) {
-        storePtr(ImmWord(0), Address(obj, UnboxedPlainObject::offsetOfExpando()));
-        if (initContents)
-            initUnboxedObjectContents(obj, &templateObj->as<UnboxedPlainObject>());
-    } else if (templateObj->is<UnboxedArrayObject>()) {
-        MOZ_ASSERT(templateObj->as<UnboxedArrayObject>().hasInlineElements());
-        int elementsOffset = UnboxedArrayObject::offsetOfInlineElements();
-        computeEffectiveAddress(Address(obj, elementsOffset), temp);
-        storePtr(temp, Address(obj, UnboxedArrayObject::offsetOfElements()));
-        store32(Imm32(templateObj->as<UnboxedArrayObject>().length()),
-                Address(obj, UnboxedArrayObject::offsetOfLength()));
-        uint32_t capacityIndex = templateObj->as<UnboxedArrayObject>().capacityIndex();
-        store32(Imm32(capacityIndex << UnboxedArrayObject::CapacityShift),
-                Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()));
     } else {
         MOZ_CRASH("Unknown object");
     }
@@ -1312,29 +1030,6 @@ MacroAssembler::initGCThing(Register obj, Register temp, JSObject* templateObj,
 }
 
 void
-MacroAssembler::initUnboxedObjectContents(Register object, UnboxedPlainObject* templateObject)
-{
-    const UnboxedLayout& layout = templateObject->layoutDontCheckGeneration();
-
-    // Initialize reference fields of the object, per UnboxedPlainObject::create.
-    if (const int32_t* list = layout.traceList()) {
-        while (*list != -1) {
-            storePtr(ImmGCPtr(GetJitContext()->runtime->names().empty),
-                     Address(object, UnboxedPlainObject::offsetOfData() + *list));
-            list++;
-        }
-        list++;
-        while (*list != -1) {
-            storePtr(ImmWord(0),
-                     Address(object, UnboxedPlainObject::offsetOfData() + *list));
-            list++;
-        }
-        // Unboxed objects don't have Values to initialize.
-        MOZ_ASSERT(*(list + 1) == -1);
-    }
-}
-
-void
 MacroAssembler::compareStrings(JSOp op, Register left, Register right, Register result,
                                Label* fail)
 {
diff --git a/js/src/jit/MacroAssembler.h b/js/src/jit/MacroAssembler.h
index b6616321c..d5cc95839 100644
--- a/js/src/jit/MacroAssembler.h
+++ b/js/src/jit/MacroAssembler.h
@@ -36,7 +36,6 @@
 #include "vm/ProxyObject.h"
 #include "vm/Shape.h"
 #include "vm/TypedArrayObject.h"
-#include "vm/UnboxedObject.h"
 
 using mozilla::FloatingPoint;
 
@@ -1626,20 +1625,6 @@ class MacroAssembler : public MacroAssemblerSpecific
     void storeToTypedFloatArray(Scalar::Type arrayType, FloatRegister value, const Address& dest,
                                 unsigned numElems = 0);
 
-    // Load a property from an UnboxedPlainObject or UnboxedArrayObject.
-    template <typename T>
-    void loadUnboxedProperty(T address, JSValueType type, TypedOrValueRegister output);
-
-    // Store a property to an UnboxedPlainObject, without triggering barriers.
-    // If failure is null, the value definitely has a type suitable for storing
-    // in the property.
-    template <typename T>
-    void storeUnboxedProperty(T address, JSValueType type,
-                              const ConstantOrRegister& value, Label* failure);
-
-    void checkUnboxedArrayCapacity(Register obj, const RegisterOrInt32Constant& index,
-                                   Register temp, Label* failure);
-
     Register extractString(const Address& address, Register scratch) {
         return extractObject(address, scratch);
     }
@@ -1716,8 +1701,6 @@ class MacroAssembler : public MacroAssemblerSpecific
                              LiveRegisterSet liveRegs, Label* fail,
                              TypedArrayObject* templateObj, TypedArrayLength lengthKind);
 
-    void initUnboxedObjectContents(Register object, UnboxedPlainObject* templateObject);
-
     void newGCString(Register result, Register temp, Label* fail);
     void newGCFatInlineString(Register result, Register temp, Label* fail);
 
diff --git a/js/src/jit/OptimizationTracking.cpp b/js/src/jit/OptimizationTracking.cpp
index 308def041..7d72795a0 100644
--- a/js/src/jit/OptimizationTracking.cpp
+++ b/js/src/jit/OptimizationTracking.cpp
@@ -844,8 +844,6 @@ MaybeConstructorFromType(TypeSet::Type ty)
         return nullptr;
     ObjectGroup* obj = ty.group();
     TypeNewScript* newScript = obj->newScript();
-    if (!newScript && obj->maybeUnboxedLayout())
-        newScript = obj->unboxedLayout().newScript();
     return newScript ? newScript->function() : nullptr;
 }
 
diff --git a/js/src/jit/Recover.cpp b/js/src/jit/Recover.cpp
index 13bf9224b..793b631df 100644
--- a/js/src/jit/Recover.cpp
+++ b/js/src/jit/Recover.cpp
@@ -1354,7 +1354,7 @@ RNewArray::recover(JSContext* cx, SnapshotIterator& iter) const
     RootedValue result(cx);
     RootedObjectGroup group(cx, templateObject->group());
 
-    JSObject* resultObject = NewFullyAllocatedArrayTryUseGroup(cx, group, count_);
+    ArrayObject* resultObject = NewFullyAllocatedArrayTryUseGroup(cx, group, count_);
     if (!resultObject)
         return false;
 
@@ -1539,37 +1539,12 @@ RObjectState::recover(JSContext* cx, SnapshotIterator& iter) const
     RootedObject object(cx, &iter.read().toObject());
     RootedValue val(cx);
 
-    if (object->is<UnboxedPlainObject>()) {
-        const UnboxedLayout& layout = object->as<UnboxedPlainObject>().layout();
+    RootedNativeObject nativeObject(cx, &object->as<NativeObject>());
+    MOZ_ASSERT(nativeObject->slotSpan() == numSlots());
 
-        RootedId id(cx);
-        RootedValue receiver(cx, ObjectValue(*object));
-        const UnboxedLayout::PropertyVector& properties = layout.properties();
-        for (size_t i = 0; i < properties.length(); i++) {
-            val = iter.read();
-
-            // This is the default placeholder value of MObjectState, when no
-            // properties are defined yet.
-            if (val.isUndefined())
-                continue;
-
-            id = NameToId(properties[i].name);
-            ObjectOpResult result;
-
-            // SetProperty can only fail due to OOM.
-            if (!SetProperty(cx, object, id, val, receiver, result))
-                return false;
-            if (!result)
-                return result.reportError(cx, object, id);
-        }
-    } else {
-        RootedNativeObject nativeObject(cx, &object->as<NativeObject>());
-        MOZ_ASSERT(nativeObject->slotSpan() == numSlots());
-
-        for (size_t i = 0; i < numSlots(); i++) {
-            val = iter.read();
-            nativeObject->setSlot(i, val);
-        }
+    for (size_t i = 0; i < numSlots(); i++) {
+        val = iter.read();
+        nativeObject->setSlot(i, val);
     }
 
     val.setObject(*object);
diff --git a/js/src/jit/ScalarReplacement.cpp b/js/src/jit/ScalarReplacement.cpp
index 4614b2162..97ba52349 100644
--- a/js/src/jit/ScalarReplacement.cpp
+++ b/js/src/jit/ScalarReplacement.cpp
@@ -13,7 +13,6 @@
 #include "jit/MIR.h"
 #include "jit/MIRGenerator.h"
 #include "jit/MIRGraph.h"
-#include "vm/UnboxedObject.h"
 
 #include "jsobjinlines.h"
 
@@ -183,25 +182,6 @@ IsObjectEscaped(MInstruction* ins, JSObject* objDefault)
             JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
             return true;
 
-          case MDefinition::Op_LoadUnboxedScalar:
-          case MDefinition::Op_StoreUnboxedScalar:
-          case MDefinition::Op_LoadUnboxedObjectOrNull:
-          case MDefinition::Op_StoreUnboxedObjectOrNull:
-          case MDefinition::Op_LoadUnboxedString:
-          case MDefinition::Op_StoreUnboxedString:
-            // Not escaped if it is the first argument.
-            if (def->indexOf(*i) != 0) {
-                JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
-                return true;
-            }
-
-            if (!def->getOperand(1)->isConstant()) {
-                JitSpewDef(JitSpew_Escape, "is addressed with unknown index\n", def);
-                return true;
-            }
-
-            break;
-
           case MDefinition::Op_PostWriteBarrier:
             break;
 
@@ -305,16 +285,6 @@ class ObjectMemoryView : public MDefinitionVisitorDefaultNoop
     void visitGuardShape(MGuardShape* ins);
     void visitFunctionEnvironment(MFunctionEnvironment* ins);
     void visitLambda(MLambda* ins);
-    void visitStoreUnboxedScalar(MStoreUnboxedScalar* ins);
-    void visitLoadUnboxedScalar(MLoadUnboxedScalar* ins);
-    void visitStoreUnboxedObjectOrNull(MStoreUnboxedObjectOrNull* ins);
-    void visitLoadUnboxedObjectOrNull(MLoadUnboxedObjectOrNull* ins);
-    void visitStoreUnboxedString(MStoreUnboxedString* ins);
-    void visitLoadUnboxedString(MLoadUnboxedString* ins);
-
-  private:
-    void storeOffset(MInstruction* ins, size_t offset, MDefinition* value);
-    void loadOffset(MInstruction* ins, size_t offset);
 };
 
 const char* ObjectMemoryView::phaseName = "Scalar Replacement of Object";
@@ -656,121 +626,6 @@ ObjectMemoryView::visitLambda(MLambda* ins)
     ins->setIncompleteObject();
 }
 
-static size_t
-GetOffsetOf(MDefinition* index, size_t width, int32_t baseOffset)
-{
-    int32_t idx = index->toConstant()->toInt32();
-    MOZ_ASSERT(idx >= 0);
-    MOZ_ASSERT(baseOffset >= 0 && size_t(baseOffset) >= UnboxedPlainObject::offsetOfData());
-    return idx * width + baseOffset - UnboxedPlainObject::offsetOfData();
-}
-
-static size_t
-GetOffsetOf(MDefinition* index, Scalar::Type type, int32_t baseOffset)
-{
-    return GetOffsetOf(index, Scalar::byteSize(type), baseOffset);
-}
-
-void
-ObjectMemoryView::storeOffset(MInstruction* ins, size_t offset, MDefinition* value)
-{
-    // Clone the state and update the slot value.
-    MOZ_ASSERT(state_->hasOffset(offset));
-    state_ = BlockState::Copy(alloc_, state_);
-    if (!state_) {
-        oom_ = true;
-        return;
-    }
-
-    state_->setOffset(offset, value);
-    ins->block()->insertBefore(ins, state_);
-
-    // Remove original instruction.
-    ins->block()->discard(ins);
-}
-
-void
-ObjectMemoryView::loadOffset(MInstruction* ins, size_t offset)
-{
-    // Replace load by the slot value.
-    MOZ_ASSERT(state_->hasOffset(offset));
-    ins->replaceAllUsesWith(state_->getOffset(offset));
-
-    // Remove original instruction.
-    ins->block()->discard(ins);
-}
-
-void
-ObjectMemoryView::visitStoreUnboxedScalar(MStoreUnboxedScalar* ins)
-{
-    // Skip stores made on other objects.
-    if (ins->elements() != obj_)
-        return;
-
-    size_t offset = GetOffsetOf(ins->index(), ins->storageType(), ins->offsetAdjustment());
-    storeOffset(ins, offset, ins->value());
-}
-
-void
-ObjectMemoryView::visitLoadUnboxedScalar(MLoadUnboxedScalar* ins)
-{
-    // Skip loads made on other objects.
-    if (ins->elements() != obj_)
-        return;
-
-    // Replace load by the slot value.
-    size_t offset = GetOffsetOf(ins->index(), ins->storageType(), ins->offsetAdjustment());
-    loadOffset(ins, offset);
-}
-
-void
-ObjectMemoryView::visitStoreUnboxedObjectOrNull(MStoreUnboxedObjectOrNull* ins)
-{
-    // Skip stores made on other objects.
-    if (ins->elements() != obj_)
-        return;
-
-    // Clone the state and update the slot value.
-    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
-    storeOffset(ins, offset, ins->value());
-}
-
-void
-ObjectMemoryView::visitLoadUnboxedObjectOrNull(MLoadUnboxedObjectOrNull* ins)
-{
-    // Skip loads made on other objects.
-    if (ins->elements() != obj_)
-        return;
-
-    // Replace load by the slot value.
-    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
-    loadOffset(ins, offset);
-}
-
-void
-ObjectMemoryView::visitStoreUnboxedString(MStoreUnboxedString* ins)
-{
-    // Skip stores made on other objects.
-    if (ins->elements() != obj_)
-        return;
-
-    // Clone the state and update the slot value.
-    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
-    storeOffset(ins, offset, ins->value());
-}
-
-void
-ObjectMemoryView::visitLoadUnboxedString(MLoadUnboxedString* ins)
-{
-    // Skip loads made on other objects.
-    if (ins->elements() != obj_)
-        return;
-
-    // Replace load by the slot value.
-    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
-    loadOffset(ins, offset);
-}
-
 static bool
 IndexOf(MDefinition* ins, int32_t* res)
 {
@@ -907,11 +762,6 @@ IsArrayEscaped(MInstruction* ins)
         return true;
     }
 
-    if (obj->is<UnboxedArrayObject>()) {
-        JitSpew(JitSpew_Escape, "Template object is an unboxed plain object.");
-        return true;
-    }
-
     if (length >= 16) {
         JitSpew(JitSpew_Escape, "Array has too many elements");
         return true;
diff --git a/js/src/jit/SharedIC.cpp b/js/src/jit/SharedIC.cpp
index 767cff661..05a95824f 100644
--- a/js/src/jit/SharedIC.cpp
+++ b/js/src/jit/SharedIC.cpp
@@ -27,6 +27,7 @@
 #endif
 #include "jit/VMFunctions.h"
 #include "vm/Interpreter.h"
+#include "vm/NativeObject-inl.h"
 
 #include "jit/MacroAssembler-inl.h"
 #include "vm/Interpreter-inl.h"
@@ -285,11 +286,6 @@ ICStub::trace(JSTracer* trc)
         TraceEdge(trc, &getElemStub->shape(), "baseline-getelem-dense-shape");
         break;
       }
-      case ICStub::GetElem_UnboxedArray: {
-        ICGetElem_UnboxedArray* getElemStub = toGetElem_UnboxedArray();
-        TraceEdge(trc, &getElemStub->group(), "baseline-getelem-unboxed-array-group");
-        break;
-      }
       case ICStub::GetElem_TypedArray: {
         ICGetElem_TypedArray* getElemStub = toGetElem_TypedArray();
         TraceEdge(trc, &getElemStub->shape(), "baseline-getelem-typedarray-shape");
@@ -2248,9 +2244,7 @@ IsCacheableProtoChain(JSObject* obj, JSObject* holder, bool isDOMProxy)
     if (!isDOMProxy && !obj->isNative()) {
         if (obj == holder)
             return false;
-        if (!obj->is<UnboxedPlainObject>() &&
-            !obj->is<UnboxedArrayObject>() &&
-            !obj->is<TypedObject>())
+        if (!obj->is<TypedObject>())
         {
             return false;
         }
@@ -2578,12 +2572,6 @@ CheckHasNoSuchProperty(JSContext* cx, JSObject* obj, PropertyName* name,
         } else if (curObj != obj) {
             // Non-native objects are only handled as the original receiver.
             return false;
-        } else if (curObj->is<UnboxedPlainObject>()) {
-            if (curObj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, NameToId(name)))
-                return false;
-        } else if (curObj->is<UnboxedArrayObject>()) {
-            if (name == cx->names().length)
-                return false;
         } else if (curObj->is<TypedObject>()) {
             if (curObj->as<TypedObject>().typeDescr().hasProperty(cx->names(), NameToId(name)))
                 return false;
@@ -2848,34 +2836,15 @@ GuardReceiverObject(MacroAssembler& masm, ReceiverGuard guard,
 {
     Address groupAddress(ICStubReg, receiverGuardOffset + HeapReceiverGuard::offsetOfGroup());
     Address shapeAddress(ICStubReg, receiverGuardOffset + HeapReceiverGuard::offsetOfShape());
-    Address expandoAddress(object, UnboxedPlainObject::offsetOfExpando());
 
     if (guard.group) {
         masm.loadPtr(groupAddress, scratch);
         masm.branchTestObjGroup(Assembler::NotEqual, object, scratch, failure);
-
-        if (guard.group->clasp() == &UnboxedPlainObject::class_ && !guard.shape) {
-            // Guard the unboxed object has no expando object.
-            masm.branchPtr(Assembler::NotEqual, expandoAddress, ImmWord(0), failure);
-        }
     }
 
     if (guard.shape) {
         masm.loadPtr(shapeAddress, scratch);
-        if (guard.group && guard.group->clasp() == &UnboxedPlainObject::class_) {
-            // Guard the unboxed object has a matching expando object.
-            masm.branchPtr(Assembler::Equal, expandoAddress, ImmWord(0), failure);
-            Label done;
-            masm.push(object);
-            masm.loadPtr(expandoAddress, object);
-            masm.branchTestObjShape(Assembler::Equal, object, scratch, &done);
-            masm.pop(object);
-            masm.jump(failure);
-            masm.bind(&done);
-            masm.pop(object);
-        } else {
-            masm.branchTestObjShape(Assembler::NotEqual, object, scratch, failure);
-        }
+        masm.branchTestObjShape(Assembler::NotEqual, object, scratch, failure);
     }
 }
 
@@ -4259,8 +4228,7 @@ DoNewObject(JSContext* cx, void* payload, ICNewObject_Fallback* stub, MutableHan
                 return false;
 
             if (!stub->invalid() &&
-                (templateObject->is<UnboxedPlainObject>() ||
-                 !templateObject->as<PlainObject>().hasDynamicSlots()))
+                !templateObject->as<PlainObject>().hasDynamicSlots())
             {
                 JitCode* code = GenerateNewObjectWithTemplateCode(cx, templateObject);
                 if (!code)
diff --git a/js/src/jit/VMFunctions.cpp b/js/src/jit/VMFunctions.cpp
index 77b9e3647..402d910b9 100644
--- a/js/src/jit/VMFunctions.cpp
+++ b/js/src/jit/VMFunctions.cpp
@@ -28,7 +28,7 @@
 #include "vm/NativeObject-inl.h"
 #include "vm/StringObject-inl.h"
 #include "vm/TypeInference-inl.h"
-#include "vm/UnboxedObject-inl.h"
+#include "gc/StoreBuffer-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -318,7 +318,7 @@ ArraySpliceDense(JSContext* cx, HandleObject obj, uint32_t start, uint32_t delet
 bool
 ArrayPopDense(JSContext* cx, HandleObject obj, MutableHandleValue rval)
 {
-    MOZ_ASSERT(obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>());
+    MOZ_ASSERT(obj->is<ArrayObject>());
 
     AutoDetectInvalidation adi(cx, rval);
 
@@ -337,12 +337,11 @@ ArrayPopDense(JSContext* cx, HandleObject obj, MutableHandleValue rval)
 }
 
 bool
-ArrayPushDense(JSContext* cx, HandleObject obj, HandleValue v, uint32_t* length)
+ArrayPushDense(JSContext* cx, HandleArrayObject arr, HandleValue v, uint32_t* length)
 {
-    *length = GetAnyBoxedOrUnboxedArrayLength(obj);
-    DenseElementResult result =
-        SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, *length, v.address(), 1,
-                                                  ShouldUpdateTypes::DontUpdate);
+    *length = arr->length();
+    DenseElementResult result = arr->setOrExtendDenseElements(cx, *length, v.address(), 1,
+                                                              ShouldUpdateTypes::DontUpdate);
     if (result != DenseElementResult::Incomplete) {
         (*length)++;
         return result == DenseElementResult::Success;
@@ -350,7 +349,7 @@ ArrayPushDense(JSContext* cx, HandleObject obj, HandleValue v, uint32_t* length)
 
     JS::AutoValueArray<3> argv(cx);
     argv[0].setUndefined();
-    argv[1].setObject(*obj);
+    argv[1].setObject(*arr);
     argv[2].set(v);
     if (!js::array_push(cx, 1, argv.begin()))
         return false;
@@ -362,7 +361,7 @@ ArrayPushDense(JSContext* cx, HandleObject obj, HandleValue v, uint32_t* length)
 bool
 ArrayShiftDense(JSContext* cx, HandleObject obj, MutableHandleValue rval)
 {
-    MOZ_ASSERT(obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>());
+    MOZ_ASSERT(obj->is<ArrayObject>());
 
     AutoDetectInvalidation adi(cx, rval);
 
@@ -1143,16 +1142,14 @@ Recompile(JSContext* cx)
 }
 
 bool
-SetDenseOrUnboxedArrayElement(JSContext* cx, HandleObject obj, int32_t index,
-                              HandleValue value, bool strict)
+SetDenseElement(JSContext* cx, HandleNativeObject obj, int32_t index, HandleValue value, bool strict)
 {
     // This function is called from Ion code for StoreElementHole's OOL path.
-    // In this case we know the object is native or an unboxed array and that
-    // no type changes are needed.
+    // In this case we know the object is native and that no type changes are
+	// needed.
 
-    DenseElementResult result =
-        SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, index, value.address(), 1,
-                                                  ShouldUpdateTypes::DontUpdate);
+    DenseElementResult result = obj->setOrExtendDenseElements(cx, index, value.address(), 1,
+                                                              ShouldUpdateTypes::DontUpdate);
     if (result != DenseElementResult::Incomplete)
         return result == DenseElementResult::Success;
 
diff --git a/js/src/jit/VMFunctions.h b/js/src/jit/VMFunctions.h
index 572f05373..9a2edd0f3 100644
--- a/js/src/jit/VMFunctions.h
+++ b/js/src/jit/VMFunctions.h
@@ -622,7 +622,7 @@ template<bool Equal>
 bool StringsEqual(JSContext* cx, HandleString left, HandleString right, bool* res);
 
 MOZ_MUST_USE bool ArrayPopDense(JSContext* cx, HandleObject obj, MutableHandleValue rval);
-MOZ_MUST_USE bool ArrayPushDense(JSContext* cx, HandleObject obj, HandleValue v, uint32_t* length);
+MOZ_MUST_USE bool ArrayPushDense(JSContext* cx, HandleArrayObject obj, HandleValue v, uint32_t* length);
 MOZ_MUST_USE bool ArrayShiftDense(JSContext* cx, HandleObject obj, MutableHandleValue rval);
 JSString* ArrayJoin(JSContext* cx, HandleObject array, HandleString sep);
 
@@ -748,8 +748,8 @@ ForcedRecompile(JSContext* cx);
 JSString* StringReplace(JSContext* cx, HandleString string, HandleString pattern,
                         HandleString repl);
 
-MOZ_MUST_USE bool SetDenseOrUnboxedArrayElement(JSContext* cx, HandleObject obj, int32_t index,
-                                                HandleValue value, bool strict);
+MOZ_MUST_USE bool SetDenseElement(JSContext* cx, HandleNativeObject obj, int32_t index,
+                                  HandleValue value, bool strict);
 
 void AssertValidObjectPtr(JSContext* cx, JSObject* obj);
 void AssertValidObjectOrNullPtr(JSContext* cx, JSObject* obj);
diff --git a/js/src/jit/arm/Assembler-arm.cpp b/js/src/jit/arm/Assembler-arm.cpp
index 2830f0695..1e20da1c8 100644
--- a/js/src/jit/arm/Assembler-arm.cpp
+++ b/js/src/jit/arm/Assembler-arm.cpp
@@ -2401,7 +2401,12 @@ Assembler::as_b(Label* l, Condition c)
         if (oom())
             return BufferOffset();
 
-        as_b(BufferOffset(l).diffB<BOffImm>(ret), c, ret);
+        BOffImm off = BufferOffset(l).diffB<BOffImm>(ret);
+        if (off.isInvalid()) {
+            m_buffer.fail_bail();
+            return BufferOffset();
+        }
+        as_b(off, c, ret);
 #ifdef JS_DISASM_ARM
         spewBranch(m_buffer.getInstOrNull(ret), l);
 #endif
diff --git a/js/src/jit/arm/MacroAssembler-arm.cpp b/js/src/jit/arm/MacroAssembler-arm.cpp
index d40578514..a4161ab00 100644
--- a/js/src/jit/arm/MacroAssembler-arm.cpp
+++ b/js/src/jit/arm/MacroAssembler-arm.cpp
@@ -5012,7 +5012,10 @@ void
 MacroAssembler::patchCall(uint32_t callerOffset, uint32_t calleeOffset)
 {
     BufferOffset inst(callerOffset - 4);
-    as_bl(BufferOffset(calleeOffset).diffB<BOffImm>(inst), Always, inst);
+    BOffImm off = BufferOffset(calleeOffset).diffB<BOffImm>(inst);
+    MOZ_RELEASE_ASSERT(!off.isInvalid(),
+                       "Failed to insert necessary far jump islands");
+    as_bl(off, Always, inst);
 }
 
 CodeOffset
diff --git a/js/src/jit/shared/LIR-shared.h b/js/src/jit/shared/LIR-shared.h
index f4adcc63c..ffa4d8367 100644
--- a/js/src/jit/shared/LIR-shared.h
+++ b/js/src/jit/shared/LIR-shared.h
@@ -5165,72 +5165,6 @@ class LSetInitializedLength : public LInstructionHelper<0, 2, 0>
     }
 };
 
-class LUnboxedArrayLength : public LInstructionHelper<1, 1, 0>
-{
-  public:
-    LIR_HEADER(UnboxedArrayLength)
-
-    explicit LUnboxedArrayLength(const LAllocation& object) {
-        setOperand(0, object);
-    }
-
-    const LAllocation* object() {
-        return getOperand(0);
-    }
-};
-
-class LUnboxedArrayInitializedLength : public LInstructionHelper<1, 1, 0>
-{
-  public:
-    LIR_HEADER(UnboxedArrayInitializedLength)
-
-    explicit LUnboxedArrayInitializedLength(const LAllocation& object) {
-        setOperand(0, object);
-    }
-
-    const LAllocation* object() {
-        return getOperand(0);
-    }
-};
-
-class LIncrementUnboxedArrayInitializedLength : public LInstructionHelper<0, 1, 0>
-{
-  public:
-    LIR_HEADER(IncrementUnboxedArrayInitializedLength)
-
-    explicit LIncrementUnboxedArrayInitializedLength(const LAllocation& object) {
-        setOperand(0, object);
-    }
-
-    const LAllocation* object() {
-        return getOperand(0);
-    }
-};
-
-class LSetUnboxedArrayInitializedLength : public LInstructionHelper<0, 2, 1>
-{
-  public:
-    LIR_HEADER(SetUnboxedArrayInitializedLength)
-
-    explicit LSetUnboxedArrayInitializedLength(const LAllocation& object,
-                                               const LAllocation& length,
-                                               const LDefinition& temp) {
-        setOperand(0, object);
-        setOperand(1, length);
-        setTemp(0, temp);
-    }
-
-    const LAllocation* object() {
-        return getOperand(0);
-    }
-    const LAllocation* length() {
-        return getOperand(1);
-    }
-    const LDefinition* temp() {
-        return getTemp(0);
-    }
-};
-
 // Load the length from an elements header.
 class LArrayLength : public LInstructionHelper<1, 1, 0>
 {
@@ -5735,19 +5669,17 @@ class LStoreElementT : public LInstructionHelper<0, 3, 0>
 };
 
 // Like LStoreElementV, but supports indexes >= initialized length.
-class LStoreElementHoleV : public LInstructionHelper<0, 3 + BOX_PIECES, 1>
+class LStoreElementHoleV : public LInstructionHelper<0, 3 + BOX_PIECES, 0>
 {
   public:
     LIR_HEADER(StoreElementHoleV)
 
     LStoreElementHoleV(const LAllocation& object, const LAllocation& elements,
-                       const LAllocation& index, const LBoxAllocation& value,
-                       const LDefinition& temp) {
+                       const LAllocation& index, const LBoxAllocation& value) {
         setOperand(0, object);
         setOperand(1, elements);
         setOperand(2, index);
         setBoxOperand(Value, value);
-        setTemp(0, temp);
     }
 
     static const size_t Value = 3;
@@ -5767,19 +5699,17 @@ class LStoreElementHoleV : public LInstructionHelper<0, 3 + BOX_PIECES, 1>
 };
 
 // Like LStoreElementT, but supports indexes >= initialized length.
-class LStoreElementHoleT : public LInstructionHelper<0, 4, 1>
+class LStoreElementHoleT : public LInstructionHelper<0, 4, 0>
 {
   public:
     LIR_HEADER(StoreElementHoleT)
 
     LStoreElementHoleT(const LAllocation& object, const LAllocation& elements,
-                       const LAllocation& index, const LAllocation& value,
-                       const LDefinition& temp) {
+                       const LAllocation& index, const LAllocation& value) {
         setOperand(0, object);
         setOperand(1, elements);
         setOperand(2, index);
         setOperand(3, value);
-        setTemp(0, temp);
     }
 
     const MStoreElementHole* mir() const {
@@ -5800,19 +5730,17 @@ class LStoreElementHoleT : public LInstructionHelper<0, 4, 1>
 };
 
 // Like LStoreElementV, but can just ignore assignment (for eg. frozen objects)
-class LFallibleStoreElementV : public LInstructionHelper<0, 3 + BOX_PIECES, 1>
+class LFallibleStoreElementV : public LInstructionHelper<0, 3 + BOX_PIECES, 0>
 {
   public:
     LIR_HEADER(FallibleStoreElementV)
 
     LFallibleStoreElementV(const LAllocation& object, const LAllocation& elements,
-                           const LAllocation& index, const LBoxAllocation& value,
-                           const LDefinition& temp) {
+                           const LAllocation& index, const LBoxAllocation& value) {
         setOperand(0, object);
         setOperand(1, elements);
         setOperand(2, index);
         setBoxOperand(Value, value);
-        setTemp(0, temp);
     }
 
     static const size_t Value = 3;
@@ -5832,19 +5760,17 @@ class LFallibleStoreElementV : public LInstructionHelper<0, 3 + BOX_PIECES, 1>
 };
 
 // Like LStoreElementT, but can just ignore assignment (for eg. frozen objects)
-class LFallibleStoreElementT : public LInstructionHelper<0, 4, 1>
+class LFallibleStoreElementT : public LInstructionHelper<0, 4, 0>
 {
   public:
     LIR_HEADER(FallibleStoreElementT)
 
     LFallibleStoreElementT(const LAllocation& object, const LAllocation& elements,
-                           const LAllocation& index, const LAllocation& value,
-                           const LDefinition& temp) {
+                           const LAllocation& index, const LAllocation& value) {
         setOperand(0, object);
         setOperand(1, elements);
         setOperand(2, index);
         setOperand(3, value);
-        setTemp(0, temp);
     }
 
     const MFallibleStoreElement* mir() const {
@@ -5891,22 +5817,6 @@ class LStoreUnboxedPointer : public LInstructionHelper<0, 3, 0>
     }
 };
 
-// If necessary, convert an unboxed object in a particular group to its native
-// representation.
-class LConvertUnboxedObjectToNative : public LInstructionHelper<0, 1, 0>
-{
-  public:
-    LIR_HEADER(ConvertUnboxedObjectToNative)
-
-    explicit LConvertUnboxedObjectToNative(const LAllocation& object) {
-        setOperand(0, object);
-    }
-
-    MConvertUnboxedObjectToNative* mir() {
-        return mir_->toConvertUnboxedObjectToNative();
-    }
-};
-
 class LArrayPopShiftV : public LInstructionHelper<BOX_PIECES, 1, 2>
 {
   public:
@@ -7429,38 +7339,6 @@ class LGuardReceiverPolymorphic : public LInstructionHelper<0, 1, 1>
     }
 };
 
-class LGuardUnboxedExpando : public LInstructionHelper<0, 1, 0>
-{
-  public:
-    LIR_HEADER(GuardUnboxedExpando)
-
-    explicit LGuardUnboxedExpando(const LAllocation& in) {
-        setOperand(0, in);
-    }
-    const LAllocation* object() {
-        return getOperand(0);
-    }
-    const MGuardUnboxedExpando* mir() const {
-        return mir_->toGuardUnboxedExpando();
-    }
-};
-
-class LLoadUnboxedExpando : public LInstructionHelper<1, 1, 0>
-{
-  public:
-    LIR_HEADER(LoadUnboxedExpando)
-
-    explicit LLoadUnboxedExpando(const LAllocation& in) {
-        setOperand(0, in);
-    }
-    const LAllocation* object() {
-        return getOperand(0);
-    }
-    const MLoadUnboxedExpando* mir() const {
-        return mir_->toLoadUnboxedExpando();
-    }
-};
-
 // Guard that a value is in a TypeSet.
 class LTypeBarrierV : public LInstructionHelper<0, BOX_PIECES, 1>
 {
diff --git a/js/src/jit/shared/LOpcodes-shared.h b/js/src/jit/shared/LOpcodes-shared.h
index fe2ab5ea3..deae92839 100644
--- a/js/src/jit/shared/LOpcodes-shared.h
+++ b/js/src/jit/shared/LOpcodes-shared.h
@@ -258,8 +258,6 @@
     _(GuardObjectGroup)             \
     _(GuardObjectIdentity)          \
     _(GuardClass)                   \
-    _(GuardUnboxedExpando)          \
-    _(LoadUnboxedExpando)           \
     _(TypeBarrierV)                 \
     _(TypeBarrierO)                 \
     _(MonitorTypes)                 \
@@ -269,10 +267,6 @@
     _(PostWriteElementBarrierV)     \
     _(InitializedLength)            \
     _(SetInitializedLength)         \
-    _(UnboxedArrayLength)           \
-    _(UnboxedArrayInitializedLength) \
-    _(IncrementUnboxedArrayInitializedLength) \
-    _(SetUnboxedArrayInitializedLength) \
     _(BoundsCheck)                  \
     _(BoundsCheckRange)             \
     _(BoundsCheckLower)             \
@@ -287,7 +281,6 @@
     _(StoreElementT)                \
     _(StoreUnboxedScalar)           \
     _(StoreUnboxedPointer)          \
-    _(ConvertUnboxedObjectToNative) \
     _(ArrayPopShiftV)               \
     _(ArrayPopShiftT)               \
     _(ArrayPushV)                   \
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index f78f94dc1..9ee29ffe4 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -6434,9 +6434,6 @@ JS_SetGlobalJitCompilerOption(JSContext* cx, JSJitCompilerOption opt, uint32_t v
         }
         jit::JitOptions.jumpThreshold = value;
         break;
-      case JSJITCOMPILER_UNBOXED_OBJECTS:
-        jit::JitOptions.disableUnboxedObjects = !value;
-        break;
       case JSJITCOMPILER_ASMJS_ATOMICS_ENABLE:
         jit::JitOptions.asmJSAtomicsEnable = !!value;
         break;
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 1f726f2e5..3f65dad34 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -1093,7 +1093,6 @@ class JS_PUBLIC_API(ContextOptions) {
         wasmAlwaysBaseline_(false),
         throwOnAsmJSValidationFailure_(false),
         nativeRegExp_(true),
-        unboxedArrays_(false),
         asyncStack_(true),
         throwOnDebuggeeWouldRun_(true),
         dumpStackOnDebuggeeWouldRun_(false),
@@ -1170,12 +1169,6 @@ class JS_PUBLIC_API(ContextOptions) {
         return *this;
     }
 
-    bool unboxedArrays() const { return unboxedArrays_; }
-    ContextOptions& setUnboxedArrays(bool flag) {
-        unboxedArrays_ = flag;
-        return *this;
-    }
-
     bool asyncStack() const { return asyncStack_; }
     ContextOptions& setAsyncStack(bool flag) {
         asyncStack_ = flag;
@@ -1238,7 +1231,6 @@ class JS_PUBLIC_API(ContextOptions) {
     bool wasmAlwaysBaseline_ : 1;
     bool throwOnAsmJSValidationFailure_ : 1;
     bool nativeRegExp_ : 1;
-    bool unboxedArrays_ : 1;
     bool asyncStack_ : 1;
     bool throwOnDebuggeeWouldRun_ : 1;
     bool dumpStackOnDebuggeeWouldRun_ : 1;
@@ -5783,20 +5775,19 @@ JS_SetParallelParsingEnabled(JSContext* cx, bool enabled);
 extern JS_PUBLIC_API(void)
 JS_SetOffthreadIonCompilationEnabled(JSContext* cx, bool enabled);
 
-#define JIT_COMPILER_OPTIONS(Register)                                      \
-    Register(BASELINE_WARMUP_TRIGGER, "baseline.warmup.trigger")            \
-    Register(ION_WARMUP_TRIGGER, "ion.warmup.trigger")                      \
-    Register(ION_GVN_ENABLE, "ion.gvn.enable")                              \
-    Register(ION_FORCE_IC, "ion.forceinlineCaches")                         \
-    Register(ION_ENABLE, "ion.enable")                                      \
+#define JIT_COMPILER_OPTIONS(Register)                                     \
+    Register(BASELINE_WARMUP_TRIGGER, "baseline.warmup.trigger")           \
+    Register(ION_WARMUP_TRIGGER, "ion.warmup.trigger")                     \
+    Register(ION_GVN_ENABLE, "ion.gvn.enable")                             \
+    Register(ION_FORCE_IC, "ion.forceinlineCaches")                        \
+    Register(ION_ENABLE, "ion.enable")                                     \
     Register(ION_INTERRUPT_WITHOUT_SIGNAL, "ion.interrupt-without-signals") \
-    Register(ION_CHECK_RANGE_ANALYSIS, "ion.check-range-analysis")          \
-    Register(BASELINE_ENABLE, "baseline.enable")                            \
-    Register(OFFTHREAD_COMPILATION_ENABLE, "offthread-compilation.enable")  \
-    Register(JUMP_THRESHOLD, "jump-threshold")                              \
-    Register(UNBOXED_OBJECTS, "unboxed_objects")                            \
-    Register(ASMJS_ATOMICS_ENABLE, "asmjs.atomics.enable")                  \
-    Register(WASM_TEST_MODE, "wasm.test-mode")                              \
+    Register(ION_CHECK_RANGE_ANALYSIS, "ion.check-range-analysis")         \
+    Register(BASELINE_ENABLE, "baseline.enable")                           \
+    Register(OFFTHREAD_COMPILATION_ENABLE, "offthread-compilation.enable") \
+    Register(JUMP_THRESHOLD, "jump-threshold")                             \
+    Register(ASMJS_ATOMICS_ENABLE, "asmjs.atomics.enable")                 \
+    Register(WASM_TEST_MODE, "wasm.test-mode")                             \
     Register(WASM_FOLD_OFFSETS, "wasm.fold-offsets")
 
 typedef enum JSJitCompilerOption {
diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index 7a67c0095..ec65bce64 100644
--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -45,7 +45,6 @@
 #include "vm/Caches-inl.h"
 #include "vm/Interpreter-inl.h"
 #include "vm/NativeObject-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using namespace js;
 using namespace js::gc;
@@ -64,7 +63,7 @@ using JS::ToUint32;
 bool
 JS::IsArray(JSContext* cx, HandleObject obj, IsArrayAnswer* answer)
 {
-    if (obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>()) {
+    if (obj->is<ArrayObject>()) {
         *answer = IsArrayAnswer::Array;
         return true;
     }
@@ -100,11 +99,6 @@ js::GetLengthProperty(JSContext* cx, HandleObject obj, uint32_t* lengthp)
         return true;
     }
 
-    if (obj->is<UnboxedArrayObject>()) {
-        *lengthp = obj->as<UnboxedArrayObject>().length();
-        return true;
-    }
-
     if (obj->is<ArgumentsObject>()) {
         ArgumentsObject& argsobj = obj->as<ArgumentsObject>();
         if (!argsobj.hasOverriddenLength()) {
@@ -253,18 +247,20 @@ static bool
 GetElement(JSContext* cx, HandleObject obj, HandleObject receiver,
            uint32_t index, bool* hole, MutableHandleValue vp)
 {
-    AssertGreaterThanZero(index);
-    if (index < GetAnyBoxedOrUnboxedInitializedLength(obj)) {
-        vp.set(GetAnyBoxedOrUnboxedDenseElement(obj, uint32_t(index)));
-        if (!vp.isMagic(JS_ELEMENTS_HOLE)) {
-            *hole = false;
-            return true;
+    if (obj->isNative()) {
+        NativeObject* nobj = &obj->as<NativeObject>();
+        if (index < nobj->getDenseInitializedLength()) {
+            vp.set(nobj->getDenseElement(size_t(index)));
+            if (!vp.isMagic(JS_ELEMENTS_HOLE)) {
+                *hole = false;
+                return true;
+            }
         }
-    }
-    if (obj->is<ArgumentsObject>()) {
-        if (obj->as<ArgumentsObject>().maybeGetElement(uint32_t(index), vp)) {
-            *hole = false;
-            return true;
+        if (nobj->is<ArgumentsObject>() && index <= UINT32_MAX) {
+            if (nobj->as<ArgumentsObject>().maybeGetElement(uint32_t(index), vp)) {
+                *hole = false;
+                return true;
+            }
         }
     }
 
@@ -283,8 +279,8 @@ ElementAdder::append(JSContext* cx, HandleValue v)
 {
     MOZ_ASSERT(index_ < length_);
     if (resObj_) {
-        DenseElementResult result =
-            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, resObj_, index_, v.address(), 1);
+        NativeObject* resObj = &resObj_->as<NativeObject>();
+        DenseElementResult result = resObj->setOrExtendDenseElements(cx, index_, v.address(), 1);
         if (result == DenseElementResult::Failure)
             return false;
         if (result == DenseElementResult::Incomplete) {
@@ -336,37 +332,31 @@ js::GetElementsWithAdder(JSContext* cx, HandleObject obj, HandleObject receiver,
     return true;
 }
 
-template <JSValueType Type>
-DenseElementResult
-GetBoxedOrUnboxedDenseElements(JSObject* aobj, uint32_t length, Value* vp)
+static bool
+GetDenseElements(NativeObject* aobj, uint32_t length, Value* vp)
 {
     MOZ_ASSERT(!ObjectMayHaveExtraIndexedProperties(aobj));
 
-    if (length > GetBoxedOrUnboxedInitializedLength<Type>(aobj))
-        return DenseElementResult::Incomplete;
+    if (length > aobj->getDenseInitializedLength())
+        return false;
 
     for (size_t i = 0; i < length; i++) {
-        vp[i] = GetBoxedOrUnboxedDenseElement<Type>(aobj, i);
+        vp[i] = aobj->getDenseElement(i);
 
         // No other indexed properties so hole => undefined.
         if (vp[i].isMagic(JS_ELEMENTS_HOLE))
             vp[i] = UndefinedValue();
     }
 
-    return DenseElementResult::Success;
+    return true;
 }
 
-DefineBoxedOrUnboxedFunctor3(GetBoxedOrUnboxedDenseElements,
-                             JSObject*, uint32_t, Value*);
-
 bool
 js::GetElements(JSContext* cx, HandleObject aobj, uint32_t length, Value* vp)
 {
     if (!ObjectMayHaveExtraIndexedProperties(aobj)) {
-        GetBoxedOrUnboxedDenseElementsFunctor functor(aobj, length, vp);
-        DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, aobj);
-        if (result != DenseElementResult::Incomplete)
-            return result == DenseElementResult::Success;
+        if (GetDenseElements(&aobj->as<NativeObject>(), length, vp))
+            return true;
     }
 
     if (aobj->is<ArgumentsObject>()) {
@@ -398,9 +388,9 @@ SetArrayElement(JSContext* cx, HandleObject obj, double index, HandleValue v)
 {
     MOZ_ASSERT(index >= 0);
 
-    if ((obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>()) && !obj->isIndexed() && index <= UINT32_MAX) {
-        DenseElementResult result =
-            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, uint32_t(index), v.address(), 1);
+    if (obj->is<ArrayObject>() && !obj->isIndexed() && index <= UINT32_MAX) {
+        NativeObject* nobj = &obj->as<NativeObject>();
+        DenseElementResult result = nobj->setOrExtendDenseElements(cx, uint32_t(index), v.address(), 1);
         if (result != DenseElementResult::Incomplete)
             return result == DenseElementResult::Success;
     }
@@ -520,24 +510,6 @@ struct ReverseIndexComparator
     }
 };
 
-bool
-js::CanonicalizeArrayLengthValue(JSContext* cx, HandleValue v, uint32_t* newLen)
-{
-    double d;
-
-    if (!ToUint32(cx, v, newLen))
-        return false;
-
-    if (!ToNumber(cx, v, &d))
-        return false;
-
-    if (d == *newLen)
-        return true;
-
-    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
-    return false;
-}
-
 /* ES6 draft rev 34 (2015 Feb 20) 9.4.2.4 ArraySetLength */
 bool
 js::ArraySetLength(JSContext* cx, Handle<ArrayObject*> arr, HandleId id,
@@ -559,12 +531,22 @@ js::ArraySetLength(JSContext* cx, Handle<ArrayObject*> arr, HandleId id,
     } else {
         // Step 2 is irrelevant in our implementation.
 
-        // Steps 3-7.
-        MOZ_ASSERT_IF(attrs & JSPROP_IGNORE_VALUE, value.isUndefined());
-        if (!CanonicalizeArrayLengthValue(cx, value, &newLen))
+        // Step 3.
+        if (!ToUint32(cx, value, &newLen))
+            return false;
+
+        // Step 4.
+        double d;
+        if (!ToNumber(cx, value, &d))
             return false;
 
-        // Step 8 is irrelevant in our implementation.
+        // Step 5.
+        if (d != newLen) {
+            JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
+            return false;
+        }
+
+        // Steps 6-8 are irrelevant in our implementation.
     }
 
     // Steps 9-11.
@@ -823,7 +805,7 @@ array_addProperty(JSContext* cx, HandleObject obj, HandleId id, HandleValue v)
 static inline bool
 ObjectMayHaveExtraIndexedOwnProperties(JSObject* obj)
 {
-    return (!obj->isNative() && !obj->is<UnboxedArrayObject>()) ||
+    return !obj->isNative() ||
            obj->isIndexed() ||
            obj->is<TypedArrayObject>() ||
            ClassMayResolveId(*obj->runtimeFromAnyThread()->commonNames,
@@ -854,7 +836,7 @@ js::ObjectMayHaveExtraIndexedProperties(JSObject* obj)
 
         if (ObjectMayHaveExtraIndexedOwnProperties(obj))
             return true;
-        if (GetAnyBoxedOrUnboxedInitializedLength(obj) != 0)
+        if (obj->as<NativeObject>().getDenseInitializedLength() != 0)
             return true;
     } while (true);
 }
@@ -1064,31 +1046,32 @@ struct StringSeparatorOp
     }
 };
 
-template <typename SeparatorOp, JSValueType Type>
-static DenseElementResult
-ArrayJoinDenseKernel(JSContext* cx, SeparatorOp sepOp, HandleObject obj, uint32_t length,
+template <typename SeparatorOp>
+static bool
+ArrayJoinDenseKernel(JSContext* cx, SeparatorOp sepOp, HandleNativeObject obj, uint64_t length,
                      StringBuffer& sb, uint32_t* numProcessed)
 {
     // This loop handles all elements up to initializedLength. If
     // length > initLength we rely on the second loop to add the
     // other elements.
     MOZ_ASSERT(*numProcessed == 0);
-    uint32_t initLength = Min<uint32_t>(GetBoxedOrUnboxedInitializedLength<Type>(obj), length);
+    uint32_t initLength = Min<uint32_t>(obj->getDenseInitializedLength(),
+                                        length);
     while (*numProcessed < initLength) {
         if (!CheckForInterrupt(cx))
-            return DenseElementResult::Failure;
+            return false;
 
-        Value elem = GetBoxedOrUnboxedDenseElement<Type>(obj, *numProcessed);
+        Value elem = obj->as<NativeObject>().getDenseElement(*numProcessed);
 
         if (elem.isString()) {
             if (!sb.append(elem.toString()))
-                return DenseElementResult::Failure;
+                return false;
         } else if (elem.isNumber()) {
             if (!NumberValueToStringBuffer(cx, elem, sb))
-                return DenseElementResult::Failure;
+                return false;
         } else if (elem.isBoolean()) {
             if (!BooleanToStringBuffer(elem.toBoolean(), sb))
-                return DenseElementResult::Failure;
+                return false;
         } else if (elem.isObject() || elem.isSymbol()) {
             /*
              * Object stringifying could modify the initialized length or make
@@ -1104,33 +1087,13 @@ ArrayJoinDenseKernel(JSContext* cx, SeparatorOp sepOp, HandleObject obj, uint32_
         }
 
         if (++(*numProcessed) != length && !sepOp(cx, sb))
-            return DenseElementResult::Failure;
+            return false;
     }
 
-    return DenseElementResult::Incomplete;
+    return true;
 }
 
 template <typename SeparatorOp>
-struct ArrayJoinDenseKernelFunctor {
-    JSContext* cx;
-    SeparatorOp sepOp;
-    HandleObject obj;
-    uint32_t length;
-    StringBuffer& sb;
-    uint32_t* numProcessed;
-
-    ArrayJoinDenseKernelFunctor(JSContext* cx, SeparatorOp sepOp, HandleObject obj,
-                                uint32_t length, StringBuffer& sb, uint32_t* numProcessed)
-      : cx(cx), sepOp(sepOp), obj(obj), length(length), sb(sb), numProcessed(numProcessed)
-    {}
-
-    template <JSValueType Type>
-    DenseElementResult operator()() {
-        return ArrayJoinDenseKernel<SeparatorOp, Type>(cx, sepOp, obj, length, sb, numProcessed);
-    }
-};
-
-template <typename SeparatorOp>
 static bool
 ArrayJoinKernel(JSContext* cx, SeparatorOp sepOp, HandleObject obj, uint32_t length,
                StringBuffer& sb)
@@ -1138,10 +1101,10 @@ ArrayJoinKernel(JSContext* cx, SeparatorOp sepOp, HandleObject obj, uint32_t len
     uint32_t i = 0;
 
     if (!ObjectMayHaveExtraIndexedProperties(obj)) {
-        ArrayJoinDenseKernelFunctor<SeparatorOp> functor(cx, sepOp, obj, length, sb, &i);
-        DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, obj);
-        if (result == DenseElementResult::Failure)
+        if (!ArrayJoinDenseKernel<SeparatorOp>(cx, sepOp, obj.as<NativeObject>(), length, sb, &i))
+        {
             return false;
+        }
     }
 
     if (i != length) {
@@ -1212,11 +1175,14 @@ js::array_join(JSContext* cx, unsigned argc, Value* vp)
     // An optimized version of a special case of steps 7-11: when length==1 and
     // the 0th element is a string, ToString() of that element is a no-op and
     // so it can be immediately returned as the result.
-    if (length == 1 && GetAnyBoxedOrUnboxedInitializedLength(obj) == 1) {
-        Value elem0 = GetAnyBoxedOrUnboxedDenseElement(obj, 0);
-        if (elem0.isString()) {
-            args.rval().set(elem0);
-            return true;
+    if (length == 1 && obj->isNative()) {
+        NativeObject* nobj = &obj->as<NativeObject>();
+        if (nobj->getDenseInitializedLength() == 1) {
+            Value elem0 = nobj->getDenseElement(0);
+            if (elem0.isString()) {
+                args.rval().set(elem0);
+                return true;
+            }
         }
     }
 
@@ -1259,7 +1225,7 @@ js::array_join(JSContext* cx, unsigned argc, Value* vp)
     }
 
     // Step 11
-    JSString *str = sb.finishString();
+    JSString* str = sb.finishString();
     if (!str)
         return false;
 
@@ -1288,10 +1254,6 @@ array_toLocaleString(JSContext* cx, unsigned argc, Value* vp)
         args.rval().setString(cx->names().empty);
         return true;
     }
-    if (obj->is<UnboxedArrayObject>() && obj->as<UnboxedArrayObject>().length() == 0) {
-        args.rval().setString(cx->names().empty);
-        return true;
-    }
 
     AutoCycleDetector detector(cx, obj);
     if (!detector.init())
@@ -1328,8 +1290,9 @@ InitArrayElements(JSContext* cx, HandleObject obj, uint32_t start,
         return false;
 
     if (!ObjectMayHaveExtraIndexedProperties(obj)) {
-        DenseElementResult result =
-            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, start, vector, count, updateTypes);
+        NativeObject* nobj = &obj->as<NativeObject>();
+        DenseElementResult result = nobj->setOrExtendDenseElements(cx, uint32_t(start), vector,
+                                                                   count, updateTypes);
         if (result != DenseElementResult::Incomplete)
             return result == DenseElementResult::Success;
     }
@@ -1363,54 +1326,45 @@ InitArrayElements(JSContext* cx, HandleObject obj, uint32_t start,
     return true;
 }
 
-template <JSValueType Type>
-DenseElementResult
-ArrayReverseDenseKernel(JSContext* cx, HandleObject obj, uint32_t length)
+static DenseElementResult
+ArrayReverseDenseKernel(JSContext* cx, HandleNativeObject obj, uint32_t length)
 {
     /* An empty array or an array with no elements is already reversed. */
-    if (length == 0 || GetBoxedOrUnboxedInitializedLength<Type>(obj) == 0)
+    if (length == 0 || obj->getDenseInitializedLength() == 0)
         return DenseElementResult::Success;
 
-    if (Type == JSVAL_TYPE_MAGIC) {
-        if (obj->as<NativeObject>().denseElementsAreFrozen())
-            return DenseElementResult::Incomplete;
+    if (obj->denseElementsAreFrozen())
+        return DenseElementResult::Incomplete;
 
-        /*
-         * It's actually surprisingly complicated to reverse an array due to the
-         * orthogonality of array length and array capacity while handling
-         * leading and trailing holes correctly.  Reversing seems less likely to
-         * be a common operation than other array mass-mutation methods, so for
-         * now just take a probably-small memory hit (in the absence of too many
-         * holes in the array at its start) and ensure that the capacity is
-         * sufficient to hold all the elements in the array if it were full.
-         */
-        DenseElementResult result = obj->as<NativeObject>().ensureDenseElements(cx, length, 0);
-        if (result != DenseElementResult::Success)
-            return result;
+    /*
+     * It's actually surprisingly complicated to reverse an array due to the
+     * orthogonality of array length and array capacity while handling
+     * leading and trailing holes correctly.  Reversing seems less likely to
+     * be a common operation than other array mass-mutation methods, so for
+     * now just take a probably-small memory hit (in the absence of too many
+     * holes in the array at its start) and ensure that the capacity is
+     * sufficient to hold all the elements in the array if it were full.
+     */
+    DenseElementResult result = obj->ensureDenseElements(cx, length, 0);
+    if (result != DenseElementResult::Success)
+        return result;
 
-        /* Fill out the array's initialized length to its proper length. */
-        obj->as<NativeObject>().ensureDenseInitializedLength(cx, length, 0);
-    } else {
-        // Unboxed arrays can only be reversed here if their initialized length
-        // matches their actual length. Otherwise the reversal will place holes
-        // at the beginning of the array, which we don't support.
-        if (length != obj->as<UnboxedArrayObject>().initializedLength())
-            return DenseElementResult::Incomplete;
-    }
+    /* Fill out the array's initialized length to its proper length. */
+    obj->ensureDenseInitializedLength(cx, length, 0);
 
     RootedValue origlo(cx), orighi(cx);
 
     uint32_t lo = 0, hi = length - 1;
     for (; lo < hi; lo++, hi--) {
-        origlo = GetBoxedOrUnboxedDenseElement<Type>(obj, lo);
-        orighi = GetBoxedOrUnboxedDenseElement<Type>(obj, hi);
-        SetBoxedOrUnboxedDenseElementNoTypeChange<Type>(obj, lo, orighi);
+        origlo = obj->getDenseElement(lo);
+        orighi = obj->getDenseElement(hi);
+        obj->setDenseElement(lo, orighi);
         if (orighi.isMagic(JS_ELEMENTS_HOLE) &&
             !SuppressDeletedProperty(cx, obj, INT_TO_JSID(lo)))
         {
             return DenseElementResult::Failure;
         }
-        SetBoxedOrUnboxedDenseElementNoTypeChange<Type>(obj, hi, origlo);
+        obj->setDenseElement(hi, origlo);
         if (origlo.isMagic(JS_ELEMENTS_HOLE) &&
             !SuppressDeletedProperty(cx, obj, INT_TO_JSID(hi)))
         {
@@ -1421,9 +1375,6 @@ ArrayReverseDenseKernel(JSContext* cx, HandleObject obj, uint32_t length)
     return DenseElementResult::Success;
 }
 
-DefineBoxedOrUnboxedFunctor3(ArrayReverseDenseKernel,
-                             JSContext*, HandleObject, uint32_t);
-
 bool
 js::array_reverse(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -1438,8 +1389,8 @@ js::array_reverse(JSContext* cx, unsigned argc, Value* vp)
         return false;
 
     if (!ObjectMayHaveExtraIndexedProperties(obj)) {
-        ArrayReverseDenseKernelFunctor functor(cx, obj, len);
-        DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, obj);
+        DenseElementResult result =
+            ArrayReverseDenseKernel(cx, obj.as<NativeObject>(), uint32_t(len));
         if (result != DenseElementResult::Incomplete) {
             /*
              * Per ECMA-262, don't update the length of the array, even if the new
@@ -2082,8 +2033,8 @@ js::array_push(JSContext* cx, unsigned argc, Value* vp)
 
     if (!ObjectMayHaveExtraIndexedProperties(obj)) {
         DenseElementResult result =
-            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, length,
-                                                      args.array(), args.length());
+            obj->as<NativeObject>().setOrExtendDenseElements(cx, uint32_t(length),
+                                                             args.array(), args.length());
         if (result != DenseElementResult::Incomplete) {
             if (result == DenseElementResult::Failure)
                 return false;
@@ -2091,14 +2042,8 @@ js::array_push(JSContext* cx, unsigned argc, Value* vp)
             uint32_t newlength = length + args.length();
             args.rval().setNumber(newlength);
 
-            // SetOrExtendAnyBoxedOrUnboxedDenseElements takes care of updating the
-            // length for boxed and unboxed arrays. Handle updates to the length of
-            // non-arrays here.
-            bool isArray;
-            if (!IsArray(cx, obj, &isArray))
-                return false;
-
-            if (!isArray)
+            // Handle updates to the length of non-arrays here.
+            if (!obj->is<ArrayObject>())
                 return SetLengthProperty(cx, obj, newlength);
 
             return true;
@@ -2154,42 +2099,46 @@ js::array_pop(JSContext* cx, unsigned argc, Value* vp)
     return SetLengthProperty(cx, obj, index);
 }
 
-template <JSValueType Type>
-static inline DenseElementResult
-ShiftMoveBoxedOrUnboxedDenseElements(JSObject* obj)
+void
+js::ArrayShiftMoveElements(NativeObject* obj)
 {
-    MOZ_ASSERT(HasBoxedOrUnboxedDenseElements<Type>(obj));
+    MOZ_ASSERT_IF(obj->is<ArrayObject>(), obj->as<ArrayObject>().lengthIsWritable());
+
+    size_t initlen = obj->getDenseInitializedLength();
+    MOZ_ASSERT(initlen > 0);
 
     /*
      * At this point the length and initialized length have already been
      * decremented and the result fetched, so just shift the array elements
      * themselves.
      */
-    size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
-    if (Type == JSVAL_TYPE_MAGIC) {
-        obj->as<NativeObject>().moveDenseElementsNoPreBarrier(0, 1, initlen);
-    } else {
-        uint8_t* data = obj->as<UnboxedArrayObject>().elements();
-        size_t elementSize = UnboxedTypeSize(Type);
-        memmove(data, data + elementSize, initlen * elementSize);
-    }
-
-    return DenseElementResult::Success;
+    obj->moveDenseElementsNoPreBarrier(0, 1, initlen);
 }
 
-DefineBoxedOrUnboxedFunctor1(ShiftMoveBoxedOrUnboxedDenseElements, JSObject*);
+static inline void
+SetInitializedLength(JSContext* cx, NativeObject* obj, size_t initlen)
+{
+    size_t oldInitlen = obj->getDenseInitializedLength();
+    obj->setDenseInitializedLength(initlen);
+    if (initlen < oldInitlen)
+        obj->shrinkElements(cx, initlen);
+}
 
-void
-js::ArrayShiftMoveElements(JSObject* obj)
+static DenseElementResult
+MoveDenseElements(JSContext* cx, NativeObject* obj, uint32_t dstStart, uint32_t srcStart,
+                  uint32_t length)
 {
-    MOZ_ASSERT_IF(obj->is<ArrayObject>(), obj->as<ArrayObject>().lengthIsWritable());
+    if (obj->denseElementsAreFrozen())
+        return DenseElementResult::Incomplete;
 
-    ShiftMoveBoxedOrUnboxedDenseElementsFunctor functor(obj);
-    JS_ALWAYS_TRUE(CallBoxedOrUnboxedSpecialization(functor, obj) == DenseElementResult::Success);
+    if (!obj->maybeCopyElementsForWrite(cx))
+        return DenseElementResult::Failure;
+    obj->moveDenseElements(dstStart, srcStart, length);
+
+    return DenseElementResult::Success;
 }
 
-template <JSValueType Type>
-DenseElementResult
+static DenseElementResult
 ArrayShiftDenseKernel(JSContext* cx, HandleObject obj, MutableHandleValue rval)
 {
     if (ObjectMayHaveExtraIndexedProperties(obj))
@@ -2202,25 +2151,22 @@ ArrayShiftDenseKernel(JSContext* cx, HandleObject obj, MutableHandleValue rval)
     if (MOZ_UNLIKELY(group->hasAllFlags(OBJECT_FLAG_ITERATED)))
         return DenseElementResult::Incomplete;
 
-    size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
+    size_t initlen = obj->as<NativeObject>().getDenseInitializedLength();
     if (initlen == 0)
         return DenseElementResult::Incomplete;
 
-    rval.set(GetBoxedOrUnboxedDenseElement<Type>(obj, 0));
+    rval.set(obj->as<NativeObject>().getDenseElement(0));
     if (rval.isMagic(JS_ELEMENTS_HOLE))
         rval.setUndefined();
 
-    DenseElementResult result = MoveBoxedOrUnboxedDenseElements<Type>(cx, obj, 0, 1, initlen - 1);
+    DenseElementResult result = MoveDenseElements(cx, &obj->as<NativeObject>(), 0, 1, initlen - 1);
     if (result != DenseElementResult::Success)
         return result;
 
-    SetBoxedOrUnboxedInitializedLength<Type>(cx, obj, initlen - 1);
+    SetInitializedLength(cx, obj.as<NativeObject>(), initlen - 1);
     return DenseElementResult::Success;
 }
 
-DefineBoxedOrUnboxedFunctor3(ArrayShiftDenseKernel,
-                             JSContext*, HandleObject, MutableHandleValue);
-
 /* ES5 15.4.4.9 */
 bool
 js::array_shift(JSContext* cx, unsigned argc, Value* vp)
@@ -2252,8 +2198,7 @@ js::array_shift(JSContext* cx, unsigned argc, Value* vp)
     uint32_t newlen = len - 1;
 
     /* Fast paths. */
-    ArrayShiftDenseKernelFunctor functor(cx, obj, args.rval());
-    DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, obj);
+    DenseElementResult result = ArrayShiftDenseKernel(cx, obj, args.rval());
     if (result != DenseElementResult::Incomplete) {
         if (result == DenseElementResult::Failure)
             return false;
@@ -2307,9 +2252,6 @@ js::array_unshift(JSContext* cx, unsigned argc, Value* vp)
     if (args.length() > 0) {
         /* Slide up the array to make room for all args at the bottom. */
         if (length > 0) {
-            // Only include a fast path for boxed arrays. Unboxed arrays can'nt
-            // be optimized here because unshifting temporarily places holes at
-            // the start of the array.
             bool optimized = false;
             do {
                 if (!obj->is<ArrayObject>())
@@ -2369,10 +2311,10 @@ js::array_unshift(JSContext* cx, unsigned argc, Value* vp)
 }
 
 /*
- * Returns true if this is a dense or unboxed array whose |count| properties
- * starting from |startingIndex| may be accessed (get, set, delete) directly
- * through its contiguous vector of elements without fear of getters, setters,
- * etc. along the prototype chain, or of enumerators requiring notification of
+ * Returns true if this is a dense array whose properties ending at |endIndex|
+ * (exclusive) may be accessed (get, set, delete) directly through its
+ * contiguous vector of elements without fear of getters, setters, etc. along
+ * the prototype chain, or of enumerators requiring notification of
  * modifications.
  */
 static inline bool
@@ -2383,11 +2325,11 @@ CanOptimizeForDenseStorage(HandleObject arr, uint32_t startingIndex, uint32_t co
         return false;
 
     /* There's no optimizing possible if it's not an array. */
-    if (!arr->is<ArrayObject>() && !arr->is<UnboxedArrayObject>())
+    if (!arr->is<ArrayObject>())
         return false;
 
     /* If it's a frozen array, always pick the slow path */
-    if (arr->is<ArrayObject>() && arr->as<ArrayObject>().denseElementsAreFrozen())
+    if (arr->as<ArrayObject>().denseElementsAreFrozen())
         return false;
 
     /*
@@ -2419,7 +2361,23 @@ CanOptimizeForDenseStorage(HandleObject arr, uint32_t startingIndex, uint32_t co
      * is subsumed by the initializedLength comparison.)
      */
     return !ObjectMayHaveExtraIndexedProperties(arr) &&
-           startingIndex + count <= GetAnyBoxedOrUnboxedInitializedLength(arr);
+           startingIndex + count <= arr->as<NativeObject>().getDenseInitializedLength();
+}
+
+static inline DenseElementResult
+CopyDenseElements(JSContext* cx, NativeObject* dst, NativeObject* src,
+                      uint32_t dstStart, uint32_t srcStart, uint32_t length)
+{
+    MOZ_ASSERT(dst->getDenseInitializedLength() == dstStart);
+    MOZ_ASSERT(src->getDenseInitializedLength() >= srcStart + length);
+    MOZ_ASSERT(dst->getDenseCapacity() >= dstStart + length);
+
+    dst->setDenseInitializedLength(dstStart + length);
+
+    const Value* vp = src->getDenseElements() + srcStart;
+    dst->initDenseElements(dstStart, vp, length);
+
+    return DenseElementResult::Success;
 }
 
 /* ES 2016 draft Mar 25, 2016 22.1.3.26. */
@@ -2520,7 +2478,9 @@ js::array_splice_impl(JSContext* cx, unsigned argc, Value* vp, bool returnValueI
 
                 /* Steps 10-11. */
                 DebugOnly<DenseElementResult> result =
-                    CopyAnyBoxedOrUnboxedDenseElements(cx, arr, obj, 0, actualStart, actualDeleteCount);
+                    CopyDenseElements(cx, &arr->as<NativeObject>(), 
+                                      &obj->as<NativeObject>(), 0, 
+                                      actualStart, actualDeleteCount);
                 MOZ_ASSERT(result.value == DenseElementResult::Success);
 
                 /* Step 12 (implicit). */
@@ -2557,14 +2517,13 @@ js::array_splice_impl(JSContext* cx, unsigned argc, Value* vp, bool returnValueI
         if (CanOptimizeForDenseStorage(obj, 0, len, cx)) {
             /* Steps 15.a-b. */
             DenseElementResult result =
-                MoveAnyBoxedOrUnboxedDenseElements(cx, obj, targetIndex, sourceIndex,
-                                                   len - sourceIndex);
+                MoveDenseElements(cx, &obj->as<NativeObject>(), targetIndex, sourceIndex, len - sourceIndex);
             MOZ_ASSERT(result != DenseElementResult::Incomplete);
             if (result == DenseElementResult::Failure)
                 return false;
 
             /* Steps 15.c-d. */
-            SetAnyBoxedOrUnboxedInitializedLength(cx, obj, finalLength);
+            SetInitializedLength(cx, obj.as<NativeObject>(), finalLength);
         } else {
             /*
              * This is all very slow if the length is very large. We don't yet
@@ -2644,15 +2603,15 @@ js::array_splice_impl(JSContext* cx, unsigned argc, Value* vp, bool returnValueI
 
         if (CanOptimizeForDenseStorage(obj, len, itemCount - actualDeleteCount, cx)) {
             DenseElementResult result =
-                MoveAnyBoxedOrUnboxedDenseElements(cx, obj, actualStart + itemCount,
-                                                   actualStart + actualDeleteCount,
-                                                   len - (actualStart + actualDeleteCount));
+                MoveDenseElements(cx, &obj->as<NativeObject>(), actualStart + itemCount,
+                                  actualStart + actualDeleteCount,
+                                  len - (actualStart + actualDeleteCount));
             MOZ_ASSERT(result != DenseElementResult::Incomplete);
             if (result == DenseElementResult::Failure)
                 return false;
 
             /* Steps 16.a-b. */
-            SetAnyBoxedOrUnboxedInitializedLength(cx, obj, len + itemCount - actualDeleteCount);
+            SetInitializedLength(cx, obj.as<NativeObject>(), len + itemCount - actualDeleteCount);
         } else {
             RootedValue fromValue(cx);
             for (double k = len - actualDeleteCount; k > actualStart; k--) {
@@ -2824,7 +2783,7 @@ SliceSlowly(JSContext* cx, HandleObject obj, HandleObject receiver,
 }
 
 static bool
-SliceSparse(JSContext* cx, HandleObject obj, uint32_t begin, uint32_t end, HandleObject result)
+SliceSparse(JSContext* cx, HandleObject obj, uint32_t begin, uint32_t end, HandleArrayObject result)
 {
     MOZ_ASSERT(begin <= end);
 
@@ -2874,26 +2833,28 @@ ArraySliceOrdinary(JSContext* cx, HandleObject obj, uint32_t length, uint32_t be
         begin = end;
 
     if (!ObjectMayHaveExtraIndexedProperties(obj)) {
-        size_t initlen = GetAnyBoxedOrUnboxedInitializedLength(obj);
+        size_t initlen = obj->as<NativeObject>().getDenseInitializedLength();
         size_t count = 0;
         if (initlen > begin)
             count = Min<size_t>(initlen - begin, end - begin);
 
-        RootedObject narr(cx, NewFullyAllocatedArrayTryReuseGroup(cx, obj, count));
+        RootedArrayObject narr(cx, NewFullyAllocatedArrayTryReuseGroup(cx, obj, count));
         if (!narr)
             return false;
-        SetAnyBoxedOrUnboxedArrayLength(cx, narr, end - begin);
+
+        MOZ_ASSERT(count >= narr->as<ArrayObject>().length());
+        narr->as<ArrayObject>().setLength(cx, count);
 
         if (count) {
             DebugOnly<DenseElementResult> result =
-                CopyAnyBoxedOrUnboxedDenseElements(cx, narr, obj, 0, begin, count);
+                CopyDenseElements(cx, &narr->as<NativeObject>(), &obj->as<NativeObject>(), 0, begin, count);
             MOZ_ASSERT(result.value == DenseElementResult::Success);
         }
         arr.set(narr);
         return true;
     }
 
-    RootedObject narr(cx, NewPartlyAllocatedArrayTryReuseGroup(cx, obj, end - begin));
+    RootedArrayObject narr(cx, NewPartlyAllocatedArrayTryReuseGroup(cx, obj, end - begin));
     if (!narr)
         return false;
 
@@ -3010,11 +2971,10 @@ js::array_slice(JSContext* cx, unsigned argc, Value* vp)
     return true;
 }
 
-template <JSValueType Type>
-DenseElementResult
-ArraySliceDenseKernel(JSContext* cx, JSObject* obj, int32_t beginArg, int32_t endArg, JSObject* result)
+static bool
+ArraySliceDenseKernel(JSContext* cx, ArrayObject* arr, int32_t beginArg, int32_t endArg, ArrayObject* result)
 {
-    int32_t length = GetAnyBoxedOrUnboxedArrayLength(obj);
+    int32_t length = arr->length();
 
     uint32_t begin = NormalizeSliceTerm(beginArg, length);
     uint32_t end = NormalizeSliceTerm(endArg, length);
@@ -3022,33 +2982,33 @@ ArraySliceDenseKernel(JSContext* cx, JSObject* obj, int32_t beginArg, int32_t en
     if (begin > end)
         begin = end;
 
-    size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
+    size_t initlen = arr->getDenseInitializedLength();
+    size_t count = Min<size_t>(initlen - begin, end - begin);
     if (initlen > begin) {
-        size_t count = Min<size_t>(initlen - begin, end - begin);
         if (count) {
-            DenseElementResult rv = EnsureBoxedOrUnboxedDenseElements<Type>(cx, result, count);
-            if (rv != DenseElementResult::Success)
-                return rv;
-            CopyBoxedOrUnboxedDenseElements<Type, Type>(cx, result, obj, 0, begin, count);
+            if (!result->ensureElements(cx, count))
+                return false;
+            CopyDenseElements(cx, &result->as<NativeObject>(), &arr->as<NativeObject>(), 0, begin, count);
         }
     }
 
-    SetAnyBoxedOrUnboxedArrayLength(cx, result, end - begin);
-    return DenseElementResult::Success;
-}
+    MOZ_ASSERT(count >= result->length());
+    result->setLength(cx, count);
 
-DefineBoxedOrUnboxedFunctor5(ArraySliceDenseKernel,
-                             JSContext*, JSObject*, int32_t, int32_t, JSObject*);
+    return true;
+}
 
 JSObject*
 js::array_slice_dense(JSContext* cx, HandleObject obj, int32_t begin, int32_t end,
                       HandleObject result)
 {
     if (result && IsArraySpecies(cx, obj)) {
-        ArraySliceDenseKernelFunctor functor(cx, obj, begin, end, result);
-        DenseElementResult rv = CallBoxedOrUnboxedSpecialization(functor, result);
-        MOZ_ASSERT(rv != DenseElementResult::Incomplete);
-        return rv == DenseElementResult::Success ? result : nullptr;
+        if (!ArraySliceDenseKernel(cx, &obj->as<ArrayObject>(), begin, end,
+                                   &result->as<ArrayObject>()))
+        {
+            return nullptr;
+        }
+        return result;
     }
 
     // Slower path if the JIT wasn't able to allocate an object inline.
@@ -3079,7 +3039,7 @@ array_isArray(JSContext* cx, unsigned argc, Value* vp)
 static bool
 ArrayFromCallArgs(JSContext* cx, CallArgs& args, HandleObject proto = nullptr)
 {
-    JSObject* obj = NewCopiedArrayForCallingAllocationSite(cx, args.array(), args.length(), proto);
+    ArrayObject* obj = NewCopiedArrayForCallingAllocationSite(cx, args.array(), args.length(), proto);
     if (!obj)
         return false;
 
@@ -3169,6 +3129,11 @@ static const JSFunctionSpec array_methods[] = {
 
     /* ES7 additions */
     JS_SELF_HOSTED_FN("includes",    "ArrayIncludes",    2,0),
+    
+    /* ES2019 additions */
+    JS_SELF_HOSTED_FN("flat",        "ArrayFlat",        0,0),
+    JS_SELF_HOSTED_FN("flatMap",     "ArrayFlatMap",     1,0),
+    
     JS_FS_END
 };
 
@@ -3239,7 +3204,7 @@ ArrayConstructorImpl(JSContext* cx, CallArgs& args, bool isConstructor)
         }
     }
 
-    JSObject* obj = NewPartlyAllocatedArrayForCallingAllocationSite(cx, length, proto);
+    ArrayObject* obj = NewPartlyAllocatedArrayForCallingAllocationSite(cx, length, proto);
     if (!obj)
         return false;
 
@@ -3265,7 +3230,7 @@ js::array_construct(JSContext* cx, unsigned argc, Value* vp)
     return ArrayConstructorImpl(cx, args, /* isConstructor = */ false);
 }
 
-JSObject*
+ArrayObject*
 js::ArrayConstructorOneArg(JSContext* cx, HandleObjectGroup group, int32_t lengthInt)
 {
     if (lengthInt < 0) {
@@ -3333,6 +3298,8 @@ array_proto_finish(JSContext* cx, JS::HandleObject ctor, JS::HandleObject proto)
         !DefineProperty(cx, unscopables, cx->names().fill, value) ||
         !DefineProperty(cx, unscopables, cx->names().find, value) ||
         !DefineProperty(cx, unscopables, cx->names().findIndex, value) ||
+        !DefineProperty(cx, unscopables, cx->names().flat, value) ||
+        !DefineProperty(cx, unscopables, cx->names().flatMap, value) ||
         !DefineProperty(cx, unscopables, cx->names().includes, value) ||
         !DefineProperty(cx, unscopables, cx->names().keys, value) ||
         !DefineProperty(cx, unscopables, cx->names().values, value))
@@ -3558,7 +3525,7 @@ js::NewDenseFullyAllocatedArrayWithTemplate(JSContext* cx, uint32_t length, JSOb
     return arr;
 }
 
-JSObject*
+ArrayObject*
 js::NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc::InitialHeap heap)
 {
     MOZ_ASSERT(!gc::IsInsideNursery(templateObject));
@@ -3571,30 +3538,21 @@ js::NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc
     return arr;
 }
 
-// Return a new boxed or unboxed array with the specified length and allocated
-// capacity (up to maxLength), using the specified group if possible. If the
-// specified group cannot be used, ensure that the created array at least has
-// the given [[Prototype]].
+// Return a new array with the specified length and allocated capacity (up to
+// maxLength), using the specified group if possible. If the specified group
+// cannot be used, ensure that the created array at least has the given
+// [[Prototype]].
 template <uint32_t maxLength>
-static inline JSObject*
+static inline ArrayObject*
 NewArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
                     NewObjectKind newKind = GenericObject)
 {
     MOZ_ASSERT(newKind != SingletonObject);
 
-    if (group->maybePreliminaryObjects())
-        group->maybePreliminaryObjects()->maybeAnalyze(cx, group);
-
-    if (group->shouldPreTenure() || group->maybePreliminaryObjects())
+    if (group->shouldPreTenure())
         newKind = TenuredObject;
 
     RootedObject proto(cx, group->proto().toObject());
-    if (group->maybeUnboxedLayout()) {
-        if (length > UnboxedArrayObject::MaximumCapacity)
-            return NewArray<maxLength>(cx, length, proto, newKind);
-        return UnboxedArrayObject::create(cx, group, length, newKind, maxLength);
-    }
-
     ArrayObject* res = NewArray<maxLength>(cx, length, proto, newKind);
     if (!res)
         return nullptr;
@@ -3606,20 +3564,17 @@ NewArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length
     if (res->length() > INT32_MAX)
         res->setLength(cx, res->length());
 
-    if (PreliminaryObjectArray* preliminaryObjects = group->maybePreliminaryObjects())
-        preliminaryObjects->registerNewObject(res);
-
     return res;
 }
 
-JSObject*
+ArrayObject*
 js::NewFullyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
                                       NewObjectKind newKind)
 {
     return NewArrayTryUseGroup<UINT32_MAX>(cx, group, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length)
 {
     return NewArrayTryUseGroup<ArrayObject::EagerAllocationMaxLength>(cx, group, length);
@@ -3628,16 +3583,13 @@ js::NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup g
 // Return a new array with the default prototype and specified allocated
 // capacity and length. If possible, try to reuse the group of the input
 // object. The resulting array will either reuse the input object's group or
-// will have unknown property types. Additionally, the result will have the
-// same boxed/unboxed elements representation as the input object, unless
-// |length| is larger than the input object's initialized length (in which case
-// UnboxedArrayObject::MaximumCapacity might be exceeded).
+// will have unknown property types.
 template <uint32_t maxLength>
-static inline JSObject*
+static inline ArrayObject*
 NewArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
                       NewObjectKind newKind = GenericObject)
 {
-    if (!obj->is<ArrayObject>() && !obj->is<UnboxedArrayObject>())
+    if (!obj->is<ArrayObject>())
         return NewArray<maxLength>(cx, length, nullptr, newKind);
 
     if (obj->staticPrototype() != cx->global()->maybeGetArrayPrototype())
@@ -3650,20 +3602,20 @@ NewArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
     return NewArrayTryUseGroup<maxLength>(cx, group, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewFullyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
                                         NewObjectKind newKind)
 {
     return NewArrayTryReuseGroup<UINT32_MAX>(cx, obj, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewPartlyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length)
 {
     return NewArrayTryReuseGroup<ArrayObject::EagerAllocationMaxLength>(cx, obj, length);
 }
 
-JSObject*
+ArrayObject*
 js::NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
                                                    NewObjectKind newKind)
 {
@@ -3673,7 +3625,7 @@ js::NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
     return NewArrayTryUseGroup<UINT32_MAX>(cx, group, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length, HandleObject proto)
 {
     RootedObjectGroup group(cx, ObjectGroup::callingAllocationSiteGroup(cx, JSProto_Array, proto));
@@ -3682,68 +3634,23 @@ js::NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length
     return NewArrayTryUseGroup<ArrayObject::EagerAllocationMaxLength>(cx, group, length);
 }
 
-bool
-js::MaybeAnalyzeBeforeCreatingLargeArray(ExclusiveContext* cx, HandleObjectGroup group,
-                                         const Value* vp, size_t length)
-{
-    static const size_t EagerPreliminaryObjectAnalysisThreshold = 800;
-
-    // Force analysis to see if an unboxed array can be used when making a
-    // sufficiently large array, to avoid excessive analysis and copying later
-    // on. If this is the first array of its group that is being created, first
-    // make a dummy array with the initial elements of the array we are about
-    // to make, so there is some basis for the unboxed array analysis.
-    if (length > EagerPreliminaryObjectAnalysisThreshold) {
-        if (PreliminaryObjectArrayWithTemplate* objects = group->maybePreliminaryObjects()) {
-            if (objects->empty()) {
-                size_t nlength = Min<size_t>(length, 100);
-                JSObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, nlength);
-                if (!obj)
-                    return false;
-                DebugOnly<DenseElementResult> result =
-                    SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, 0, vp, nlength,
-                                                              ShouldUpdateTypes::Update);
-                MOZ_ASSERT(result.value == DenseElementResult::Success);
-            }
-            objects->maybeAnalyze(cx, group, /* forceAnalyze = */ true);
-        }
-    }
-    return true;
-}
-
-JSObject*
+ArrayObject*
 js::NewCopiedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group,
                               const Value* vp, size_t length, NewObjectKind newKind,
                               ShouldUpdateTypes updateTypes)
 {
-    if (!MaybeAnalyzeBeforeCreatingLargeArray(cx, group, vp, length))
-        return nullptr;
-
-    JSObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, length, newKind);
+    ArrayObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, length, newKind);
     if (!obj)
         return nullptr;
 
-    DenseElementResult result =
-        SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, 0, vp, length, updateTypes);
-    if (result == DenseElementResult::Failure)
-        return nullptr;
-    if (result == DenseElementResult::Success)
-        return obj;
-
-    MOZ_ASSERT(obj->is<UnboxedArrayObject>());
-    if (!UnboxedArrayObject::convertToNative(cx->asJSContext(), obj))
-        return nullptr;
-
-    result = SetOrExtendBoxedOrUnboxedDenseElements<JSVAL_TYPE_MAGIC>(cx, obj, 0, vp, length,
-                                                                      updateTypes);
-    MOZ_ASSERT(result != DenseElementResult::Incomplete);
+    DenseElementResult result = obj->setOrExtendDenseElements(cx->asJSContext(), 0, vp, length, updateTypes);
     if (result == DenseElementResult::Failure)
         return nullptr;
-
+    MOZ_ASSERT(result == DenseElementResult::Success);
     return obj;
 }
 
-JSObject*
+ArrayObject*
 js::NewCopiedArrayForCallingAllocationSite(JSContext* cx, const Value* vp, size_t length,
                                            HandleObject proto /* = nullptr */)
 {
diff --git a/js/src/jsarray.h b/js/src/jsarray.h
index e22cde881..ec2e4f514 100644
--- a/js/src/jsarray.h
+++ b/js/src/jsarray.h
@@ -72,49 +72,37 @@ extern ArrayObject*
 NewDenseFullyAllocatedArrayWithTemplate(JSContext* cx, uint32_t length, JSObject* templateObject);
 
 /* Create a dense array with the same copy-on-write elements as another object. */
-extern JSObject*
+extern ArrayObject*
 NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc::InitialHeap heap);
 
-// The methods below can create either boxed or unboxed arrays.
-
-extern JSObject*
+extern ArrayObject*
 NewFullyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
                                   NewObjectKind newKind = GenericObject);
 
-extern JSObject*
+extern ArrayObject*
 NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length);
 
-extern JSObject*
+extern ArrayObject*
 NewFullyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
                                     NewObjectKind newKind = GenericObject);
 
-extern JSObject*
+extern ArrayObject*
 NewPartlyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length);
 
-extern JSObject*
+extern ArrayObject*
 NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
                                                NewObjectKind newKind = GenericObject);
 
-extern JSObject*
+extern ArrayObject*
 NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length, HandleObject proto);
 
-enum class ShouldUpdateTypes
-{
-    Update,
-    DontUpdate
-};
-
-extern bool
-MaybeAnalyzeBeforeCreatingLargeArray(ExclusiveContext* cx, HandleObjectGroup group,
-                                     const Value* vp, size_t length);
-
-extern JSObject*
+extern ArrayObject*
 NewCopiedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group,
                           const Value* vp, size_t length,
                           NewObjectKind newKind = GenericObject,
                           ShouldUpdateTypes updateTypes = ShouldUpdateTypes::Update);
 
-extern JSObject*
+extern ArrayObject*
 NewCopiedArrayForCallingAllocationSite(JSContext* cx, const Value* vp, size_t length,
                                        HandleObject proto = nullptr);
 
@@ -129,13 +117,6 @@ NewValuePair(JSContext* cx, const Value& val1, const Value& val2, MutableHandleV
 extern bool
 WouldDefinePastNonwritableLength(HandleNativeObject obj, uint32_t index);
 
-/*
- * Canonicalize |vp| to a uint32_t value potentially suitable for use as an
- * array length.
- */
-extern bool
-CanonicalizeArrayLengthValue(JSContext* cx, HandleValue v, uint32_t* canonicalized);
-
 extern bool
 GetLengthProperty(JSContext* cx, HandleObject obj, uint32_t* lengthp);
 
@@ -172,7 +153,7 @@ extern bool
 array_join(JSContext* cx, unsigned argc, js::Value* vp);
 
 extern void
-ArrayShiftMoveElements(JSObject* obj);
+ArrayShiftMoveElements(NativeObject* obj);
 
 extern bool
 array_shift(JSContext* cx, unsigned argc, js::Value* vp);
@@ -202,7 +183,7 @@ array_splice(JSContext* cx, unsigned argc, js::Value* vp);
 extern bool
 NewbornArrayPush(JSContext* cx, HandleObject obj, const Value& v);
 
-extern JSObject*
+extern ArrayObject*
 ArrayConstructorOneArg(JSContext* cx, HandleObjectGroup group, int32_t lengthInt);
 
 #ifdef DEBUG
diff --git a/js/src/jscompartment.h b/js/src/jscompartment.h
index 98c8fe200..83c15da3b 100644
--- a/js/src/jscompartment.h
+++ b/js/src/jscompartment.h
@@ -529,9 +529,6 @@ struct JSCompartment
     // table manages references from such typed objects to their buffers.
     js::ObjectWeakMap* lazyArrayBuffers;
 
-    // All unboxed layouts in the compartment.
-    mozilla::LinkedList<js::UnboxedLayout> unboxedLayouts;
-
     // WebAssembly state for the compartment.
     js::wasm::Compartment wasm;
 
diff --git a/js/src/jsfriendapi.cpp b/js/src/jsfriendapi.cpp
index f5cd56a9b..5baba0beb 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -269,9 +269,9 @@ js::GetBuiltinClass(JSContext* cx, HandleObject obj, ESClass* cls)
     if (MOZ_UNLIKELY(obj->is<ProxyObject>()))
         return Proxy::getBuiltinClass(cx, obj, cls);
 
-    if (obj->is<PlainObject>() || obj->is<UnboxedPlainObject>())
+    if (obj->is<PlainObject>())
         *cls = ESClass::Object;
-    else if (obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>())
+    else if (obj->is<ArrayObject>())
         *cls = ESClass::Array;
     else if (obj->is<NumberObject>())
         *cls = ESClass::Number;
diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 8cee9ec09..b2ee8d67b 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -1524,19 +1524,11 @@ GCMarker::delayMarkingChildren(const void* thing)
 }
 
 inline void
-ArenaLists::prepareForIncrementalGC(JSRuntime* rt)
+ArenaLists::prepareForIncrementalGC()
 {
+    purge();
     for (auto i : AllAllocKinds()) {
-        FreeSpan* span = freeLists[i];
-        if (span != &placeholder) {
-            if (!span->isEmpty()) {
-                Arena* arena = span->getArena();
-                arena->allocatedDuringIncremental = true;
-                rt->gc.marker.delayMarkingArena(arena);
-            } else {
-                freeLists[i] = &placeholder;
-            }
-        }
+        arenaLists[i].moveCursorToEnd(); 
     }
 }
 
@@ -2251,7 +2243,7 @@ GCRuntime::updateTypeDescrObjects(MovingTracer* trc, Zone* zone)
 {
     zone->typeDescrObjects.sweep();
     for (auto r = zone->typeDescrObjects.all(); !r.empty(); r.popFront())
-        UpdateCellPointers(trc, r.front().get());
+        UpdateCellPointers(trc, r.front());
 }
 
 void
@@ -3579,6 +3571,23 @@ RelazifyFunctions(Zone* zone, AllocKind kind)
     }
 }
 
+static bool
+ShouldCollectZone(Zone* zone, JS::gcreason::Reason reason)
+{
+    // Normally we collect all scheduled zones.
+    if (reason != JS::gcreason::COMPARTMENT_REVIVED)
+        return zone->isGCScheduled();
+	
+    // If we are repeating a GC because we noticed dead compartments haven't
+    // been collected, then only collect zones containing those compartments.
+    for (CompartmentsInZoneIter comp(zone); !comp.done(); comp.next()) {
+        if (comp->scheduledForDestruction)
+            return true;
+    }
+     
+    return false;
+}
+
 bool
 GCRuntime::beginMarkPhase(JS::gcreason::Reason reason, AutoLockForExclusiveAccess& lock)
 {
@@ -3602,7 +3611,7 @@ GCRuntime::beginMarkPhase(JS::gcreason::Reason reason, AutoLockForExclusiveAcces
 #endif
 
         /* Set up which zones will be collected. */
-        if (zone->isGCScheduled()) {
+        if (ShouldCollectZone(zone, reason)) {
             if (!zone->isAtomsZone()) {
                 any = true;
                 zone->setGCState(Zone::Mark);
@@ -3621,7 +3630,7 @@ GCRuntime::beginMarkPhase(JS::gcreason::Reason reason, AutoLockForExclusiveAcces
     for (CompartmentsIter c(rt, WithAtoms); !c.done(); c.next()) {
         c->marked = false;
         c->scheduledForDestruction = false;
-        c->maybeAlive = false;
+        c->maybeAlive = c->hasBeenEntered() || !c->zone()->isGCScheduled();
         if (shouldPreserveJITCode(c, currentTime, reason, canAllocateMoreCode))
             c->zone()->setPreservingCode(true);
     }
@@ -3641,6 +3650,7 @@ GCRuntime::beginMarkPhase(JS::gcreason::Reason reason, AutoLockForExclusiveAcces
      * on. If the value of keepAtoms() changes between GC slices, then we'll
      * cancel the incremental GC. See IsIncrementalGCSafe.
      */
+	 
     if (isFull && !rt->keepAtoms()) {
         Zone* atomsZone = rt->atomsCompartment(lock)->zone();
         if (atomsZone->isGCScheduled()) {
@@ -3655,15 +3665,12 @@ GCRuntime::beginMarkPhase(JS::gcreason::Reason reason, AutoLockForExclusiveAcces
         return false;
 
     /*
-     * At the end of each incremental slice, we call prepareForIncrementalGC,
-     * which marks objects in all arenas that we're currently allocating
-     * into. This can cause leaks if unreachable objects are in these
-     * arenas. This purge call ensures that we only mark arenas that have had
-     * allocations after the incremental GC started.
+     * Ensure that after the start of a collection we don't allocate into any
+     * existing arenas, as this can cause unreachable things to be marked.  
      */
     if (isIncremental) {
         for (GCZonesIter zone(rt); !zone.done(); zone.next())
-            zone->arenas.purge();
+            zone->arenas.prepareForIncrementalGC();
     }
 
     MemProfiler::MarkTenuredStart(rt);
@@ -3748,12 +3755,10 @@ GCRuntime::beginMarkPhase(JS::gcreason::Reason reason, AutoLockForExclusiveAcces
     gcstats::AutoPhase ap2(stats, gcstats::PHASE_MARK_ROOTS);
 
     if (isIncremental) {
-        gcstats::AutoPhase ap3(stats, gcstats::PHASE_BUFFER_GRAY_ROOTS);
         bufferGrayRoots();
+        markCompartments();
     }
-
-    markCompartments();
-
+     
     return true;
 }
 
@@ -3766,9 +3771,14 @@ GCRuntime::markCompartments()
      * This code ensures that if a compartment is "dead", then it will be
      * collected in this GC. A compartment is considered dead if its maybeAlive
      * flag is false. The maybeAlive flag is set if:
-     *   (1) the compartment has incoming cross-compartment edges, or
-     *   (2) an object in the compartment was marked during root marking, either
-     *       as a black root or a gray root.
+     *   (1) the compartment has been entered (set in beginMarkPhase() above)
+     *   (2) the compartment is not being collected (set in beginMarkPhase()
+     *       above)
+     *   (3) an object in the compartment was marked during root marking, either
+     *       as a black root or a gray root (set in RootMarking.cpp), or
+     *   (4) the compartment has incoming cross-compartment edges from another
+     *       compartment that has maybeAlive set (set by this method).
+     *
      * If the maybeAlive is false, then we set the scheduledForDestruction flag.
      * At the end of the GC, we look for compartments where
      * scheduledForDestruction is true. These are compartments that were somehow
@@ -3786,26 +3796,37 @@ GCRuntime::markCompartments()
      * allocation and read barriers during JS_TransplantObject and the like.
      */
 
-    /* Set the maybeAlive flag based on cross-compartment edges. */
-    for (CompartmentsIter c(rt, SkipAtoms); !c.done(); c.next()) {
-        for (JSCompartment::WrapperEnum e(c); !e.empty(); e.popFront()) {
+    /* Propagate the maybeAlive flag via cross-compartment edges. */
+	
+    Vector<JSCompartment*, 0, js::SystemAllocPolicy> workList;
+    
+    for (CompartmentsIter comp(rt, SkipAtoms); !comp.done(); comp.next()) {
+        if (comp->maybeAlive) {
+            if (!workList.append(comp))
+                return;
+        }
+    }
+    while (!workList.empty()) {
+        JSCompartment* comp = workList.popCopy();
+        for (JSCompartment::WrapperEnum e(comp); !e.empty(); e.popFront()) {
             if (e.front().key().is<JSString*>())
                 continue;
             JSCompartment* dest = e.front().mutableKey().compartment();
-            if (dest)
+            if (dest && !dest->maybeAlive) {
                 dest->maybeAlive = true;
+                if (!workList.append(dest))
+                    return;
+            }
         }
     }
 
-    /*
-     * For black roots, code in gc/Marking.cpp will already have set maybeAlive
-     * during MarkRuntime.
-     */
-
-    /* Propogate maybeAlive to scheduleForDestruction. */
-    for (GCCompartmentsIter c(rt); !c.done(); c.next()) {
-        if (!c->maybeAlive && !rt->isAtomsCompartment(c))
-            c->scheduledForDestruction = true;
+	
+    /* Set scheduleForDestruction based on maybeAlive. */
+	
+    for (GCCompartmentsIter comp(rt); !comp.done(); comp.next()) {
+         MOZ_ASSERT(!comp->scheduledForDestruction);
+         if (!comp->maybeAlive && !rt->isAtomsCompartment(comp))
+             comp->scheduledForDestruction = true;
     }
 }
 
@@ -5306,7 +5327,7 @@ AutoGCSlice::~AutoGCSlice()
     for (ZonesIter zone(runtime, WithAtoms); !zone.done(); zone.next()) {
         if (zone->isGCMarking()) {
             zone->setNeedsIncrementalBarrier(true, Zone::UpdateJit);
-            zone->arenas.prepareForIncrementalGC(runtime);
+            zone->arenas.purge();
         } else {
             zone->setNeedsIncrementalBarrier(false, Zone::UpdateJit);
         }
@@ -5487,7 +5508,7 @@ gc::AbortReason
 gc::IsIncrementalGCUnsafe(JSRuntime* rt)
 {
     MOZ_ASSERT(!rt->mainThread.suppressGC);
-
+	
     if (rt->keepAtoms())
         return gc::AbortReason::KeepAtomsSet;
 
@@ -5498,9 +5519,17 @@ gc::IsIncrementalGCUnsafe(JSRuntime* rt)
 }
 
 void
-GCRuntime::budgetIncrementalGC(SliceBudget& budget, AutoLockForExclusiveAccess& lock)
+GCRuntime::budgetIncrementalGC(JS::gcreason::Reason reason, SliceBudget& budget,
+                               AutoLockForExclusiveAccess& lock)
 {
     AbortReason unsafeReason = IsIncrementalGCUnsafe(rt);
+    if (unsafeReason == AbortReason::None) {
+        if (reason == JS::gcreason::COMPARTMENT_REVIVED)
+            unsafeReason = gc::AbortReason::CompartmentRevived;
+        else if (mode != JSGC_MODE_INCREMENTAL)
+            unsafeReason = gc::AbortReason::ModeChange;
+   }
+	
     if (unsafeReason != AbortReason::None) {
         resetIncrementalGC(unsafeReason, lock);
         budget.makeUnlimited();
@@ -5508,12 +5537,7 @@ GCRuntime::budgetIncrementalGC(SliceBudget& budget, AutoLockForExclusiveAccess&
         return;
     }
 
-    if (mode != JSGC_MODE_INCREMENTAL) {
-        resetIncrementalGC(AbortReason::ModeChange, lock);
-        budget.makeUnlimited();
-        stats.nonincremental(AbortReason::ModeChange);
-        return;
-    }
+  
 
     if (isTooMuchMalloc()) {
         budget.makeUnlimited();
@@ -5672,7 +5696,7 @@ GCRuntime::gcCycle(bool nonincrementalByAPI, SliceBudget& budget, JS::gcreason::
         stats.nonincremental(gc::AbortReason::NonIncrementalRequested);
         budget.makeUnlimited();
     } else {
-        budgetIncrementalGC(budget, session.lock);
+        budgetIncrementalGC(reason, budget, session.lock);
     }
 
     /* The GC was reset, so we need a do-over. */
@@ -5764,6 +5788,22 @@ GCRuntime::checkIfGCAllowedInCurrentState(JS::gcreason::Reason reason)
     return true;
 }
 
+bool
+GCRuntime::shouldRepeatForDeadZone(JS::gcreason::Reason reason)
+{
+    MOZ_ASSERT_IF(reason == JS::gcreason::COMPARTMENT_REVIVED, !isIncremental);
+    
+    if (!isIncremental || isIncrementalGCInProgress())
+         return false;
+    
+    for (CompartmentsIter c(rt, SkipAtoms); !c.done(); c.next()) {
+        if (c->scheduledForDestruction)
+            return true;
+    }
+    
+    return false;
+}
+
 void
 GCRuntime::collect(bool nonincrementalByAPI, SliceBudget budget, JS::gcreason::Reason reason)
 {
@@ -5782,27 +5822,23 @@ GCRuntime::collect(bool nonincrementalByAPI, SliceBudget budget, JS::gcreason::R
     do {
         poked = false;
         bool wasReset = gcCycle(nonincrementalByAPI, budget, reason);
-
-        /* Need to re-schedule all zones for GC. */
-        if (poked && cleanUpEverything)
+      
+        bool repeatForDeadZone = false;
+        if (poked && cleanUpEverything) {
+            /* Need to re-schedule all zones for GC. */
             JS::PrepareForFullGC(rt->contextFromMainThread());
 
-        /*
-         * This code makes an extra effort to collect compartments that we
-         * thought were dead at the start of the GC. See the large comment in
-         * beginMarkPhase.
-         */
-        bool repeatForDeadZone = false;
-        if (!nonincrementalByAPI && !isIncrementalGCInProgress()) {
-            for (CompartmentsIter c(rt, SkipAtoms); !c.done(); c.next()) {
-                if (c->scheduledForDestruction) {
-                    nonincrementalByAPI = true;
-                    repeatForDeadZone = true;
-                    reason = JS::gcreason::COMPARTMENT_REVIVED;
-                    c->zone()->scheduleGC();
-                }
-            }
+       
+        } else if (shouldRepeatForDeadZone(reason) && !wasReset) {
+		    /*
+             * This code makes an extra effort to collect compartments that we
+             * thought were dead at the start of the GC. See the large comment
+             * in beginMarkPhase.
+             */
+            repeatForDeadZone = true;
+            reason = JS::gcreason::COMPARTMENT_REVIVED;
         }
+   
 
         /*
          * If we reset an existing GC, we need to start a new one. Also, we
@@ -6154,12 +6190,6 @@ gc::MergeCompartments(JSCompartment* source, JSCompartment* target)
     for (auto group = source->zone()->cellIter<ObjectGroup>(); !group.done(); group.next()) {
         group->setGeneration(target->zone()->types.generation);
         group->compartment_ = target;
-
-        // Remove any unboxed layouts from the list in the off thread
-        // compartment. These do not need to be reinserted in the target
-        // compartment's list, as the list is not required to be complete.
-        if (UnboxedLayout* layout = group->maybeUnboxedLayoutDontCheckGeneration())
-            layout->detachFromCompartment();
     }
 
     // Fixup zone pointers in source's zone to refer to target's zone.
diff --git a/js/src/jsgc.h b/js/src/jsgc.h
index d3cf31fe7..952fd6bae 100644
--- a/js/src/jsgc.h
+++ b/js/src/jsgc.h
@@ -61,7 +61,8 @@ enum class State {
     D(ModeChange) \
     D(MallocBytesTrigger) \
     D(GCBytesTrigger) \
-    D(ZoneChange)
+    D(ZoneChange) \
+    D(CompartmentRevived)
 enum class AbortReason {
 #define MAKE_REASON(name) name,
     GC_ABORT_REASONS(MAKE_REASON)
@@ -453,6 +454,12 @@ class ArenaList {
         check();
         return !*cursorp_;
     }
+	
+    void moveCursorToEnd() {
+        while (!isCursorAtEnd()) {
+            cursorp_ = &(*cursorp_)->next;
+        }
+    }
 
     // This can return nullptr.
     Arena* arenaAfterCursor() const {
@@ -739,7 +746,7 @@ class ArenaLists
             freeLists[i] = &placeholder;
     }
 
-    inline void prepareForIncrementalGC(JSRuntime* rt);
+    inline void prepareForIncrementalGC();
 
     /* Check if this arena is in use. */
     bool arenaIsInUse(Arena* arena, AllocKind kind) const {
diff --git a/js/src/jsiter.cpp b/js/src/jsiter.cpp
index c1ae5dc15..004c7fc0d 100644
--- a/js/src/jsiter.cpp
+++ b/js/src/jsiter.cpp
@@ -157,8 +157,11 @@ SortComparatorIntegerIds(jsid a, jsid b, bool* lessOrEqualp)
 }
 
 static bool
-EnumerateNativeProperties(JSContext* cx, HandleNativeObject pobj, unsigned flags, Maybe<IdSet>& ht,
-                          AutoIdVector* props, Handle<UnboxedPlainObject*> unboxed = nullptr)
+EnumerateNativeProperties(JSContext* cx,
+                          HandleNativeObject pobj,
+						  unsigned flags,
+						  Maybe<IdSet>& ht,
+                          AutoIdVector* props)
 {
     bool enumerateSymbols;
     if (flags & JSITER_SYMBOLSONLY) {
@@ -220,16 +223,6 @@ EnumerateNativeProperties(JSContext* cx, HandleNativeObject pobj, unsigned flags
                 return false;
         }
 
-        if (unboxed) {
-            // If |unboxed| is set then |pobj| is the expando for an unboxed
-            // plain object we are enumerating. Add the unboxed properties
-            // themselves here since they are all property names that were
-            // given to the object before any of the expando's properties.
-            MOZ_ASSERT(pobj->is<UnboxedExpandoObject>());
-            if (!EnumerateExtraProperties(cx, unboxed, flags, ht, props))
-                return false;
-        }
-
         size_t initialLength = props->length();
 
         /* Collect all unique property names from this object's shape. */
@@ -355,22 +348,12 @@ Snapshot(JSContext* cx, HandleObject pobj_, unsigned flags, AutoIdVector* props)
 
     do {
         if (pobj->getOpsEnumerate()) {
-            if (pobj->is<UnboxedPlainObject>() && pobj->as<UnboxedPlainObject>().maybeExpando()) {
-                // Special case unboxed objects with an expando object.
-                RootedNativeObject expando(cx, pobj->as<UnboxedPlainObject>().maybeExpando());
-                if (!EnumerateNativeProperties(cx, expando, flags, ht, props,
-                                               pobj.as<UnboxedPlainObject>()))
-                {
-                    return false;
-                }
-            } else {
-                if (!EnumerateExtraProperties(cx, pobj, flags, ht, props))
-                    return false;
+            if (!EnumerateExtraProperties(cx, pobj, flags, ht, props))
+                return false;
 
-                if (pobj->isNative()) {
-                    if (!EnumerateNativeProperties(cx, pobj.as<NativeObject>(), flags, ht, props))
-                        return false;
-                }
+            if (pobj->isNative()) {
+                if (!EnumerateNativeProperties(cx, pobj.as<NativeObject>(), flags, ht, props))
+                    return false;
             }
         } else if (pobj->isNative()) {
             // Give the object a chance to resolve all lazy properties
@@ -785,11 +768,6 @@ CanCompareIterableObjectToCache(JSObject* obj)
 {
     if (obj->isNative())
         return obj->as<NativeObject>().hasEmptyElements();
-    if (obj->is<UnboxedPlainObject>()) {
-        if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando())
-            return expando->hasEmptyElements();
-        return true;
-    }
     return false;
 }
 
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index b17c845bb..2364f707e 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -43,6 +43,7 @@
 #include "frontend/BytecodeCompiler.h"
 #include "gc/Marking.h"
 #include "gc/Policy.h"
+#include "gc/StoreBuffer-inl.h"
 #include "jit/BaselineJIT.h"
 #include "js/MemoryMetrics.h"
 #include "js/Proxy.h"
@@ -869,9 +870,6 @@ static inline JSObject*
 CreateThisForFunctionWithGroup(JSContext* cx, HandleObjectGroup group,
                                NewObjectKind newKind)
 {
-    if (group->maybeUnboxedLayout() && newKind != SingletonObject)
-        return UnboxedPlainObject::create(cx, group, newKind);
-
     if (TypeNewScript* newScript = group->newScript()) {
         if (newScript->analyzed()) {
             // The definite properties analysis has been performed for this
@@ -1145,19 +1143,18 @@ js::CloneObject(JSContext* cx, HandleObject obj, Handle<js::TaggedProto> proto)
 }
 
 static bool
-GetScriptArrayObjectElements(JSContext* cx, HandleObject obj, MutableHandle<GCVector<Value>> values)
+GetScriptArrayObjectElements(JSContext* cx, HandleArrayObject arr, MutableHandle<GCVector<Value>> values)
 {
-    MOZ_ASSERT(!obj->isSingleton());
-    MOZ_ASSERT(obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>());
-    MOZ_ASSERT(!obj->isIndexed());
+    MOZ_ASSERT(!arr->isSingleton());
+    MOZ_ASSERT(!arr->isIndexed());
 
-    size_t length = GetAnyBoxedOrUnboxedArrayLength(obj);
+    size_t length = arr->length();
     if (!values.appendN(MagicValue(JS_ELEMENTS_HOLE), length))
         return false;
 
-    size_t initlen = GetAnyBoxedOrUnboxedInitializedLength(obj);
+    size_t initlen = arr->getDenseInitializedLength();
     for (size_t i = 0; i < initlen; i++)
-        values[i].set(GetAnyBoxedOrUnboxedDenseElement(obj, i));
+        values[i].set(arr->getDenseElement(i));
 
     return true;
 }
@@ -1166,46 +1163,27 @@ static bool
 GetScriptPlainObjectProperties(JSContext* cx, HandleObject obj,
                                MutableHandle<IdValueVector> properties)
 {
-    if (obj->is<PlainObject>()) {
-        PlainObject* nobj = &obj->as<PlainObject>();
+    MOZ_ASSERT(obj->is<PlainObject>());
+    PlainObject* nobj = &obj->as<PlainObject>();
 
-        if (!properties.appendN(IdValuePair(), nobj->slotSpan()))
-            return false;
-
-        for (Shape::Range<NoGC> r(nobj->lastProperty()); !r.empty(); r.popFront()) {
-            Shape& shape = r.front();
-            MOZ_ASSERT(shape.isDataDescriptor());
-            uint32_t slot = shape.slot();
-            properties[slot].get().id = shape.propid();
-            properties[slot].get().value = nobj->getSlot(slot);
-        }
-
-        for (size_t i = 0; i < nobj->getDenseInitializedLength(); i++) {
-            Value v = nobj->getDenseElement(i);
-            if (!v.isMagic(JS_ELEMENTS_HOLE) && !properties.append(IdValuePair(INT_TO_JSID(i), v)))
-                return false;
-        }
+    if (!properties.appendN(IdValuePair(), nobj->slotSpan()))
+        return false;
 
-        return true;
+    for (Shape::Range<NoGC> r(nobj->lastProperty()); !r.empty(); r.popFront()) {
+        Shape& shape = r.front();
+        MOZ_ASSERT(shape.isDataDescriptor());
+        uint32_t slot = shape.slot();
+        properties[slot].get().id = shape.propid();
+        properties[slot].get().value = nobj->getSlot(slot);
     }
 
-    if (obj->is<UnboxedPlainObject>()) {
-        UnboxedPlainObject* nobj = &obj->as<UnboxedPlainObject>();
-
-        const UnboxedLayout& layout = nobj->layout();
-        if (!properties.appendN(IdValuePair(), layout.properties().length()))
+    for (size_t i = 0; i < nobj->getDenseInitializedLength(); i++) {
+        Value v = nobj->getDenseElement(i);
+        if (!v.isMagic(JS_ELEMENTS_HOLE) && !properties.append(IdValuePair(INT_TO_JSID(i), v)))
             return false;
-
-        for (size_t i = 0; i < layout.properties().length(); i++) {
-            const UnboxedLayout::Property& property = layout.properties()[i];
-            properties[i].get().id = NameToId(property.name);
-            properties[i].get().value = nobj->getValue(property);
-        }
-
-        return true;
     }
 
-    MOZ_CRASH("Bad object kind");
+    return true;
 }
 
 static bool
@@ -1227,13 +1205,13 @@ js::DeepCloneObjectLiteral(JSContext* cx, HandleObject obj, NewObjectKind newKin
     /* NB: Keep this in sync with XDRObjectLiteral. */
     MOZ_ASSERT_IF(obj->isSingleton(),
                   cx->compartment()->behaviors().getSingletonsAsTemplates());
-    MOZ_ASSERT(obj->is<PlainObject>() || obj->is<UnboxedPlainObject>() ||
-               obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>());
+    MOZ_ASSERT(obj->is<PlainObject>() ||
+               obj->is<ArrayObject>());
     MOZ_ASSERT(newKind != SingletonObject);
 
-    if (obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>()) {
+    if (obj->is<ArrayObject>()) {
         Rooted<GCVector<Value>> values(cx, GCVector<Value>(cx));
-        if (!GetScriptArrayObjectElements(cx, obj, &values))
+        if (!GetScriptArrayObjectElements(cx, obj.as<ArrayObject>(), &values))
             return nullptr;
 
         // Deep clone any elements.
@@ -1347,10 +1325,8 @@ js::XDRObjectLiteral(XDRState<mode>* xdr, MutableHandleObject obj)
     {
         if (mode == XDR_ENCODE) {
             MOZ_ASSERT(obj->is<PlainObject>() ||
-                       obj->is<UnboxedPlainObject>() ||
-                       obj->is<ArrayObject>() ||
-                       obj->is<UnboxedArrayObject>());
-            isArray = (obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>()) ? 1 : 0;
+                       obj->is<ArrayObject>());
+            isArray = obj->is<ArrayObject>() ? 1 : 0;
         }
 
         if (!xdr->codeUint32(&isArray))
@@ -1362,8 +1338,11 @@ js::XDRObjectLiteral(XDRState<mode>* xdr, MutableHandleObject obj)
 
     if (isArray) {
         Rooted<GCVector<Value>> values(cx, GCVector<Value>(cx));
-        if (mode == XDR_ENCODE && !GetScriptArrayObjectElements(cx, obj, &values))
-            return false;
+        if (mode == XDR_ENCODE) {
+            RootedArrayObject arr(cx, &obj->as<ArrayObject>());
+            if (!GetScriptArrayObjectElements(cx, arr, &values))
+                return false;
+        }
 
         uint32_t initialized;
         if (mode == XDR_ENCODE)
@@ -2333,16 +2312,6 @@ js::LookupOwnPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, Shape**
         // us the resolve hook won't define a property with this id.
         if (ClassMayResolveId(cx->names(), obj->getClass(), id, obj))
             return false;
-    } else if (obj->is<UnboxedPlainObject>()) {
-        if (obj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, id)) {
-            MarkNonNativePropertyFound<NoGC>(propp);
-            return true;
-        }
-    } else if (obj->is<UnboxedArrayObject>()) {
-        if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-            MarkNonNativePropertyFound<NoGC>(propp);
-            return true;
-        }
     } else if (obj->is<TypedObject>()) {
         if (obj->as<TypedObject>().typeDescr().hasProperty(cx->names(), id)) {
             MarkNonNativePropertyFound<NoGC>(propp);
@@ -2590,11 +2559,6 @@ js::SetPrototype(JSContext* cx, HandleObject obj, HandleObject proto, JS::Object
             break;
     }
 
-    // Convert unboxed objects to their native representations before changing
-    // their prototype/group, as they depend on the group for their layout.
-    if (!MaybeConvertUnboxedObjectToNative(cx, obj))
-        return false;
-
     Rooted<TaggedProto> taggedProto(cx, TaggedProto(proto));
     if (!SetClassAndProto(cx, obj, obj->getClass(), taggedProto))
         return false;
@@ -2618,9 +2582,6 @@ js::PreventExtensions(JSContext* cx, HandleObject obj, ObjectOpResult& result, I
     if (!obj->nonProxyIsExtensible())
         return result.succeed();
 
-    if (!MaybeConvertUnboxedObjectToNative(cx, obj))
-        return false;
-
     // Force lazy properties to be resolved.
     AutoIdVector props(cx);
     if (!js::GetPropertyKeys(cx, obj, JSITER_HIDDEN | JSITER_OWNONLY, &props))
@@ -3714,22 +3675,6 @@ JSObject::allocKindForTenure(const js::Nursery& nursery) const
     if (IsProxy(this))
         return as<ProxyObject>().allocKindForTenure();
 
-    // Unboxed plain objects are sized according to the data they store.
-    if (is<UnboxedPlainObject>()) {
-        size_t nbytes = as<UnboxedPlainObject>().layoutDontCheckGeneration().size();
-        return GetGCObjectKindForBytes(UnboxedPlainObject::offsetOfData() + nbytes);
-    }
-
-    // Unboxed arrays use inline data if their size is small enough.
-    if (is<UnboxedArrayObject>()) {
-        const UnboxedArrayObject* nobj = &as<UnboxedArrayObject>();
-        size_t nbytes = UnboxedArrayObject::offsetOfInlineElements() +
-                        nobj->capacity() * nobj->elementSize();
-        if (nbytes <= JSObject::MAX_BYTE_SIZE)
-            return GetGCObjectKindForBytes(nbytes);
-        return AllocKind::OBJECT0;
-    }
-
     // Inlined typed objects are followed by their data, so make sure we copy
     // it all over to the new object.
     if (is<InlineTypedObject>()) {
diff --git a/js/src/jsobjinlines.h b/js/src/jsobjinlines.h
index 6be4d0d28..b1d817bca 100644
--- a/js/src/jsobjinlines.h
+++ b/js/src/jsobjinlines.h
@@ -32,21 +32,6 @@
 #include "vm/ShapedObject-inl.h"
 #include "vm/TypeInference-inl.h"
 
-namespace js {
-
-// This is needed here for ensureShape() below.
-inline bool
-MaybeConvertUnboxedObjectToNative(ExclusiveContext* cx, JSObject* obj)
-{
-    if (obj->is<UnboxedPlainObject>())
-        return UnboxedPlainObject::convertToNative(cx->asJSContext(), obj);
-    if (obj->is<UnboxedArrayObject>())
-        return UnboxedArrayObject::convertToNative(cx->asJSContext(), obj);
-    return true;
-}
-
-} // namespace js
-
 inline js::Shape*
 JSObject::maybeShape() const
 {
@@ -59,8 +44,6 @@ JSObject::maybeShape() const
 inline js::Shape*
 JSObject::ensureShape(js::ExclusiveContext* cx)
 {
-    if (!js::MaybeConvertUnboxedObjectToNative(cx, this))
-        return nullptr;
     js::Shape* shape = maybeShape();
     MOZ_ASSERT(shape);
     return shape;
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index e3b5708ca..d7db5129d 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -1970,14 +1970,14 @@ js::str_trim(JSContext* cx, unsigned argc, Value* vp)
 }
 
 bool
-js::str_trimLeft(JSContext* cx, unsigned argc, Value* vp)
+js::str_trimStart(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
     return TrimString(cx, args, true, false);
 }
 
 bool
-js::str_trimRight(JSContext* cx, unsigned argc, Value* vp)
+js::str_trimEnd(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
     return TrimString(cx, args, false, true);
@@ -2369,7 +2369,7 @@ js::str_replace_string_raw(JSContext* cx, HandleString string, HandleString patt
 }
 
 // ES 2016 draft Mar 25, 2016 21.1.3.17 steps 4, 8, 12-18.
-static JSObject*
+static ArrayObject*
 SplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleLinearString sep,
             HandleObjectGroup group)
 {
@@ -2466,7 +2466,7 @@ SplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleLinearS
 }
 
 // Fast-path for splitting a string into a character array via split("").
-static JSObject*
+static ArrayObject*
 CharSplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleObjectGroup group)
 {
     size_t strLength = str->length();
@@ -2491,7 +2491,7 @@ CharSplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleObj
 }
 
 // ES 2016 draft Mar 25, 2016 21.1.3.17 steps 4, 8, 12-18.
-JSObject*
+ArrayObject*
 js::str_split_string(JSContext* cx, HandleObjectGroup group, HandleString str, HandleString sep, uint32_t limit)
 
 {
@@ -2568,8 +2568,10 @@ static const JSFunctionSpec string_methods[] = {
     JS_FN("startsWith",        str_startsWith,        1,0),
     JS_FN("endsWith",          str_endsWith,          1,0),
     JS_FN("trim",              str_trim,              0,0),
-    JS_FN("trimLeft",          str_trimLeft,          0,0),
-    JS_FN("trimRight",         str_trimRight,         0,0),
+    JS_FN("trimLeft",          str_trimStart,         0,0),
+	JS_FN("trimStart",         str_trimStart,         0,0),
+    JS_FN("trimRight",         str_trimEnd,           0,0),
+	JS_FN("trimEnd",           str_trimEnd,           0,0),
     JS_FN("toLocaleLowerCase", str_toLocaleLowerCase, 0,0),
     JS_FN("toLocaleUpperCase", str_toLocaleUpperCase, 0,0),
     JS_SELF_HOSTED_FN("localeCompare", "String_localeCompare", 1,0),
@@ -2881,8 +2883,10 @@ static const JSFunctionSpec string_static_methods[] = {
     JS_SELF_HOSTED_FN("startsWith",      "String_static_startsWith",    2,0),
     JS_SELF_HOSTED_FN("endsWith",        "String_static_endsWith",      2,0),
     JS_SELF_HOSTED_FN("trim",            "String_static_trim",          1,0),
-    JS_SELF_HOSTED_FN("trimLeft",        "String_static_trimLeft",      1,0),
-    JS_SELF_HOSTED_FN("trimRight",       "String_static_trimRight",     1,0),
+    JS_SELF_HOSTED_FN("trimLeft",        "String_static_trimStart",     1,0),
+    JS_SELF_HOSTED_FN("trimStart",       "String_static_trimStart",     1,0),
+    JS_SELF_HOSTED_FN("trimRight",       "String_static_trimEnd",       1,0),
+    JS_SELF_HOSTED_FN("trimEnd",         "String_static_trimEnd",       1,0),
     JS_SELF_HOSTED_FN("toLocaleLowerCase","String_static_toLocaleLowerCase",1,0),
     JS_SELF_HOSTED_FN("toLocaleUpperCase","String_static_toLocaleUpperCase",1,0),
     JS_SELF_HOSTED_FN("normalize",       "String_static_normalize",     1,0),
diff --git a/js/src/jsstr.h b/js/src/jsstr.h
index 118118839..68175c826 100644
--- a/js/src/jsstr.h
+++ b/js/src/jsstr.h
@@ -367,10 +367,10 @@ extern bool
 str_trim(JSContext* cx, unsigned argc, Value* vp);
 
 extern bool
-str_trimLeft(JSContext* cx, unsigned argc, Value* vp);
+str_trimStart(JSContext* cx, unsigned argc, Value* vp);
 
 extern bool
-str_trimRight(JSContext* cx, unsigned argc, Value* vp);
+str_trimEnd(JSContext* cx, unsigned argc, Value* vp);
 
 extern bool
 str_toLocaleLowerCase(JSContext* cx, unsigned argc, Value* vp);
@@ -465,7 +465,7 @@ FileEscapedString(FILE* fp, const char* chars, size_t length, uint32_t quote)
     return res;
 }
 
-JSObject*
+ArrayObject*
 str_split_string(JSContext* cx, HandleObjectGroup group, HandleString str, HandleString sep,
                  uint32_t limit);
 
diff --git a/js/src/jstypes.h b/js/src/jstypes.h
index 6cfb3d4ad..04ffbe00d 100644
--- a/js/src/jstypes.h
+++ b/js/src/jstypes.h
@@ -147,7 +147,7 @@
 #  define JS_64BIT
 # endif
 #elif defined(__GNUC__)
-# if defined(__x86_64__) || defined(__64BIT__)
+# if defined(__x86_64__) || defined(__LP64__)
 #  define JS_64BIT
 # endif
 #elif defined(__xlc__) || defined(__xlC__)        /* IBM XL C/C++ */
diff --git a/js/src/jswatchpoint.cpp b/js/src/jswatchpoint.cpp
index 3cf43e219..e37323555 100644
--- a/js/src/jswatchpoint.cpp
+++ b/js/src/jswatchpoint.cpp
@@ -185,17 +185,18 @@ WatchpointMap::markAll(JSTracer* trc)
 {
     for (Map::Enum e(map); !e.empty(); e.popFront()) {
         Map::Entry& entry = e.front();
-        WatchKey key = entry.key();
-        WatchKey prior = key;
-        MOZ_ASSERT(JSID_IS_STRING(prior.id) || JSID_IS_INT(prior.id) || JSID_IS_SYMBOL(prior.id));
-
-        TraceEdge(trc, const_cast<PreBarrieredObject*>(&key.object),
-                   "held Watchpoint object");
-        TraceEdge(trc, const_cast<PreBarrieredId*>(&key.id), "WatchKey::id");
+        JSObject* object = entry.key().object;
+        jsid id = entry.key().id;
+        JSObject* priorObject = object;
+        jsid priorId = id;
+        MOZ_ASSERT(JSID_IS_STRING(priorId) || JSID_IS_INT(priorId) || JSID_IS_SYMBOL(priorId));
+
+        TraceManuallyBarrieredEdge(trc, &object, "held Watchpoint object");             
+        TraceManuallyBarrieredEdge(trc, &id, "WatchKey::id");		
         TraceEdge(trc, &entry.value().closure, "Watchpoint::closure");
 
-        if (prior.object != key.object || prior.id != key.id)
-            e.rekeyFront(key);
+        if (priorObject != object || priorId != id)
+            e.rekeyFront(WatchKey(object, id));
     }
 }
 
diff --git a/js/src/moz.build b/js/src/moz.build
index 888741138..eb30866c8 100644
--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -355,7 +355,6 @@ UNIFIED_SOURCES += [
     'vm/UbiNode.cpp',
     'vm/UbiNodeCensus.cpp',
     'vm/UbiNodeShortestPaths.cpp',
-    'vm/UnboxedObject.cpp',
     'vm/Unicode.cpp',
     'vm/Value.cpp',
     'vm/WeakMapPtr.cpp',
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 8d144417a..617b5e902 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -320,7 +320,6 @@ static bool enableIon = false;
 static bool enableAsmJS = false;
 static bool enableWasm = false;
 static bool enableNativeRegExp = false;
-static bool enableUnboxedArrays = false;
 static bool enableSharedMemory = SHARED_MEMORY_DEFAULT;
 static bool enableWasmAlwaysBaseline = false;
 static bool enableArrayProtoValues = true;
@@ -7260,7 +7259,6 @@ SetContextOptions(JSContext* cx, const OptionParser& op)
     enableAsmJS = !op.getBoolOption("no-asmjs");
     enableWasm = !op.getBoolOption("no-wasm");
     enableNativeRegExp = !op.getBoolOption("no-native-regexp");
-    enableUnboxedArrays = op.getBoolOption("unboxed-arrays");
     enableWasmAlwaysBaseline = op.getBoolOption("wasm-always-baseline");
     enableArrayProtoValues = !op.getBoolOption("no-array-proto-values");
 
@@ -7270,15 +7268,11 @@ SetContextOptions(JSContext* cx, const OptionParser& op)
                              .setWasm(enableWasm)
                              .setWasmAlwaysBaseline(enableWasmAlwaysBaseline)
                              .setNativeRegExp(enableNativeRegExp)
-                             .setUnboxedArrays(enableUnboxedArrays)
                              .setArrayProtoValues(enableArrayProtoValues);
 
     if (op.getBoolOption("wasm-check-bce"))
         jit::JitOptions.wasmAlwaysCheckBounds = true;
 
-    if (op.getBoolOption("no-unboxed-objects"))
-        jit::JitOptions.disableUnboxedObjects = true;
-
     if (const char* str = op.getStringOption("cache-ir-stubs")) {
         if (strcmp(str, "on") == 0)
             jit::JitOptions.disableCacheIR = false;
@@ -7542,7 +7536,6 @@ SetWorkerContextOptions(JSContext* cx)
                              .setWasm(enableWasm)
                              .setWasmAlwaysBaseline(enableWasmAlwaysBaseline)
                              .setNativeRegExp(enableNativeRegExp)
-                             .setUnboxedArrays(enableUnboxedArrays)
                              .setArrayProtoValues(enableArrayProtoValues);
     cx->setOffthreadIonCompilationEnabled(offthreadCompilation);
     cx->profilingScripts = enableCodeCoverage || enableDisassemblyDumps;
@@ -7712,8 +7705,6 @@ main(int argc, char** argv, char** envp)
         || !op.addBoolOption('\0', "no-asmjs", "Disable asm.js compilation")
         || !op.addBoolOption('\0', "no-wasm", "Disable WebAssembly compilation")
         || !op.addBoolOption('\0', "no-native-regexp", "Disable native regexp compilation")
-        || !op.addBoolOption('\0', "no-unboxed-objects", "Disable creating unboxed plain objects")
-        || !op.addBoolOption('\0', "unboxed-arrays", "Allow creating unboxed arrays")
         || !op.addBoolOption('\0', "wasm-always-baseline", "Enable wasm baseline compiler when possible")
         || !op.addBoolOption('\0', "wasm-check-bce", "Always generate wasm bounds check, even redundant ones.")
         || !op.addBoolOption('\0', "no-array-proto-values", "Remove Array.prototype.values")
diff --git a/js/src/tests/Intl/DateTimeFormat/timeZone_backward_links.js b/js/src/tests/Intl/DateTimeFormat/timeZone_backward_links.js
index d87abd7be..8cda44d87 100644
--- a/js/src/tests/Intl/DateTimeFormat/timeZone_backward_links.js
+++ b/js/src/tests/Intl/DateTimeFormat/timeZone_backward_links.js
@@ -1,7 +1,7 @@
 // |reftest| skip-if(!this.hasOwnProperty("Intl"))
 
 // Generated by make_intl_data.py. DO NOT EDIT.
-// tzdata version = 2018e
+// tzdata version = 2019a
 
 const tzMapper = [
     x => x,
@@ -67,6 +67,7 @@ const links = {
     "Cuba": "America/Havana",
     "Egypt": "Africa/Cairo",
     "Eire": "Europe/Dublin",
+    "Etc/UCT": "Etc/UTC",
     "GB": "Europe/London",
     "GB-Eire": "Europe/London",
     "GMT+0": "Etc/GMT",
@@ -98,7 +99,7 @@ const links = {
     "ROK": "Asia/Seoul",
     "Singapore": "Asia/Singapore",
     "Turkey": "Europe/Istanbul",
-    "UCT": "Etc/UCT",
+    "UCT": "Etc/UTC",
     "US/Alaska": "America/Anchorage",
     "US/Aleutian": "America/Adak",
     "US/Arizona": "America/Phoenix",
diff --git a/js/src/tests/Intl/DateTimeFormat/timeZone_backzone.js b/js/src/tests/Intl/DateTimeFormat/timeZone_backzone.js
index b96dac96f..a3efe0310 100644
--- a/js/src/tests/Intl/DateTimeFormat/timeZone_backzone.js
+++ b/js/src/tests/Intl/DateTimeFormat/timeZone_backzone.js
@@ -1,7 +1,7 @@
 // |reftest| skip-if(!this.hasOwnProperty("Intl"))
 
 // Generated by make_intl_data.py. DO NOT EDIT.
-// tzdata version = 2018e
+// tzdata version = 2019a
 
 const tzMapper = [
     x => x,
diff --git a/js/src/tests/Intl/DateTimeFormat/timeZone_backzone_links.js b/js/src/tests/Intl/DateTimeFormat/timeZone_backzone_links.js
index 66ef3075d..b61593f78 100644
--- a/js/src/tests/Intl/DateTimeFormat/timeZone_backzone_links.js
+++ b/js/src/tests/Intl/DateTimeFormat/timeZone_backzone_links.js
@@ -1,7 +1,7 @@
 // |reftest| skip-if(!this.hasOwnProperty("Intl"))
 
 // Generated by make_intl_data.py. DO NOT EDIT.
-// tzdata version = 2018e
+// tzdata version = 2019a
 
 const tzMapper = [
     x => x,
diff --git a/js/src/tests/Intl/DateTimeFormat/timeZone_notbackward_links.js b/js/src/tests/Intl/DateTimeFormat/timeZone_notbackward_links.js
index 8d44204bc..12b55c214 100644
--- a/js/src/tests/Intl/DateTimeFormat/timeZone_notbackward_links.js
+++ b/js/src/tests/Intl/DateTimeFormat/timeZone_notbackward_links.js
@@ -1,7 +1,7 @@
 // |reftest| skip-if(!this.hasOwnProperty("Intl"))
 
 // Generated by make_intl_data.py. DO NOT EDIT.
-// tzdata version = 2018e
+// tzdata version = 2019a
 
 const tzMapper = [
     x => x,
diff --git a/js/src/tests/ecma_6/Array/unscopables.js b/js/src/tests/ecma_6/Array/unscopables.js
index 6685309a0..56b3aa520 100644
--- a/js/src/tests/ecma_6/Array/unscopables.js
+++ b/js/src/tests/ecma_6/Array/unscopables.js
@@ -26,6 +26,8 @@ assertDeepEq(keys, [
     "fill",
     "find",
     "findIndex",
+    "flat",
+    "flatMap",
     "includes",
     "keys",
     "values"
diff --git a/js/src/tests/shell/futex.js b/js/src/tests/shell/futex.js
index b0951f12e..8ba61d71c 100644
--- a/js/src/tests/shell/futex.js
+++ b/js/src/tests/shell/futex.js
@@ -67,6 +67,8 @@ if (helperThreadCount() === 0) {
   quit();
 }
 
+var mem = new Int32Array(new SharedArrayBuffer(1024));
+
 ////////////////////////////////////////////////////////////
 
 // wait() returns "not-equal" if the value is not the expected one.
@@ -102,7 +104,7 @@ dprint("Sleeping for 2 seconds");
 sleep(2);
 dprint("Waking the main thread now");
 setSharedArrayBuffer(null);
-assertEq(Atomics.wake(mem, 0, 1), 1); // Can fail spuriously but very unlikely
+assertEq(Atomics.notify(mem, 0, 1), 1); // Can fail spuriously but very unlikely
 `);
 
 var then = Date.now();
@@ -113,14 +115,14 @@ assertEq(getSharedArrayBuffer(), null); // The worker's clearing of the mbx is v
 
 ////////////////////////////////////////////////////////////
 
-// Test the default argument to atomics.wake()
+// Test the default argument to atomics.notify()
 
 setSharedArrayBuffer(mem.buffer);
 
 evalInWorker(`
 var mem = new Int32Array(getSharedArrayBuffer());
 sleep(2);				// Probably long enough to avoid a spurious error next
-assertEq(Atomics.wake(mem, 0), 1);	// Last argument to wake should default to +Infinity
+assertEq(Atomics.notify(mem, 0), 1);	// Last argument to wake should default to +Infinity
 `);
 
 var then = Date.now();
diff --git a/js/src/vm/CommonPropertyNames.h b/js/src/vm/CommonPropertyNames.h
index e971dc844..8a36df083 100644
--- a/js/src/vm/CommonPropertyNames.h
+++ b/js/src/vm/CommonPropertyNames.h
@@ -115,6 +115,8 @@
     macro(firstDayOfWeek, firstDayOfWeek, "firstDayOfWeek") \
     macro(fix, fix, "fix") \
     macro(flags, flags, "flags") \
+    macro(flat, flat, "flat") \
+    macro(flatMap, flatMap, "flatMap") \
     macro(float32, float32, "float32") \
     macro(Float32x4, Float32x4, "Float32x4") \
     macro(float64, float64, "float64") \
diff --git a/js/src/vm/Interpreter-inl.h b/js/src/vm/Interpreter-inl.h
index 5f476c4ff..a2c8e220a 100644
--- a/js/src/vm/Interpreter-inl.h
+++ b/js/src/vm/Interpreter-inl.h
@@ -22,7 +22,6 @@
 #include "vm/EnvironmentObject-inl.h"
 #include "vm/Stack-inl.h"
 #include "vm/String-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 namespace js {
 
@@ -337,14 +336,10 @@ InitGlobalLexicalOperation(JSContext* cx, LexicalEnvironmentObject* lexicalEnvAr
 inline bool
 InitPropertyOperation(JSContext* cx, JSOp op, HandleObject obj, HandleId id, HandleValue rhs)
 {
-    if (obj->is<PlainObject>() || obj->is<JSFunction>()) {
-        unsigned propAttrs = GetInitDataPropAttrs(op);
-        return NativeDefineProperty(cx, obj.as<NativeObject>(), id, rhs, nullptr, nullptr,
-                                    propAttrs);
-    }
-
-    MOZ_ASSERT(obj->as<UnboxedPlainObject>().layout().lookup(id));
-    return PutProperty(cx, obj, id, rhs, false);
+  MOZ_ASSERT(obj->is<PlainObject>() || obj->is<JSFunction>());
+  unsigned propAttrs = GetInitDataPropAttrs(op);
+  return NativeDefineProperty(cx, obj.as<NativeObject>(), id, rhs,
+                              nullptr, nullptr, propAttrs);
 }
 
 inline bool
@@ -598,7 +593,7 @@ InitArrayElemOperation(JSContext* cx, jsbytecode* pc, HandleObject obj, uint32_t
     JSOp op = JSOp(*pc);
     MOZ_ASSERT(op == JSOP_INITELEM_ARRAY || op == JSOP_INITELEM_INC);
 
-    MOZ_ASSERT(obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>());
+    MOZ_ASSERT(obj->is<ArrayObject>());
 
     if (op == JSOP_INITELEM_INC && index == INT32_MAX) {
         JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_SPREAD_TOO_LARGE);
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index e6d6630c4..0f83c3435 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -1916,6 +1916,7 @@ CASE(EnableInterruptsPseudoOpcode)
 /* Various 1-byte no-ops. */
 CASE(JSOP_NOP)
 CASE(JSOP_NOP_DESTRUCTURING)
+CASE(JSOP_UNUSED126)
 CASE(JSOP_UNUSED192)
 CASE(JSOP_UNUSED209)
 CASE(JSOP_UNUSED210)
@@ -3636,7 +3637,6 @@ CASE(JSOP_NEWINIT)
 END_CASE(JSOP_NEWINIT)
 
 CASE(JSOP_NEWARRAY)
-CASE(JSOP_SPREADCALLARRAY)
 {
     uint32_t length = GET_UINT32(REGS.pc);
     JSObject* obj = NewArrayOperation(cx, script, REGS.pc, length);
@@ -4111,7 +4111,7 @@ CASE(JSOP_INITHOMEOBJECT)
     /* Load the home object */
     ReservedRooted<JSObject*> obj(&rootObject0);
     obj = &REGS.sp[int(-2 - skipOver)].toObject();
-    MOZ_ASSERT(obj->is<PlainObject>() || obj->is<UnboxedPlainObject>() || obj->is<JSFunction>());
+    MOZ_ASSERT(obj->is<PlainObject>() || obj->is<JSFunction>());
 
     func->setExtendedSlot(FunctionExtended::METHOD_HOMEOBJECT_SLOT, ObjectValue(*obj));
 }
@@ -4927,18 +4927,13 @@ js::NewObjectOperation(JSContext* cx, HandleScript script, jsbytecode* pc,
             return nullptr;
         if (group->maybePreliminaryObjects()) {
             group->maybePreliminaryObjects()->maybeAnalyze(cx, group);
-            if (group->maybeUnboxedLayout())
-                group->maybeUnboxedLayout()->setAllocationSite(script, pc);
         }
 
         if (group->shouldPreTenure() || group->maybePreliminaryObjects())
             newKind = TenuredObject;
-
-        if (group->maybeUnboxedLayout())
-            return UnboxedPlainObject::create(cx, group, newKind);
     }
 
-    RootedObject obj(cx);
+    RootedPlainObject obj(cx);
 
     if (*pc == JSOP_NEWOBJECT) {
         RootedPlainObject baseObject(cx, &script->getObject(pc)->as<PlainObject>());
@@ -4975,11 +4970,6 @@ js::NewObjectOperationWithTemplate(JSContext* cx, HandleObject templateObject)
 
     NewObjectKind newKind = templateObject->group()->shouldPreTenure() ? TenuredObject : GenericObject;
 
-    if (templateObject->group()->maybeUnboxedLayout()) {
-        RootedObjectGroup group(cx, templateObject->group());
-        return UnboxedPlainObject::create(cx, group, newKind);
-    }
-
     JSObject* obj = CopyInitializerObject(cx, templateObject.as<PlainObject>(), newKind);
     if (!obj)
         return nullptr;
@@ -5006,9 +4996,6 @@ js::NewArrayOperation(JSContext* cx, HandleScript script, jsbytecode* pc, uint32
 
         if (group->shouldPreTenure() || group->maybePreliminaryObjects())
             newKind = TenuredObject;
-
-        if (group->maybeUnboxedLayout())
-            return UnboxedArrayObject::create(cx, group, length, newKind);
     }
 
     ArrayObject* obj = NewDenseFullyAllocatedArray(cx, length, nullptr, newKind);
@@ -5019,9 +5006,6 @@ js::NewArrayOperation(JSContext* cx, HandleScript script, jsbytecode* pc, uint32
         MOZ_ASSERT(obj->isSingleton());
     } else {
         obj->setGroup(group);
-
-        if (PreliminaryObjectArray* preliminaryObjects = group->maybePreliminaryObjects())
-            preliminaryObjects->registerNewObject(obj);
     }
 
     return obj;
@@ -5034,12 +5018,6 @@ js::NewArrayOperationWithTemplate(JSContext* cx, HandleObject templateObject)
 
     NewObjectKind newKind = templateObject->group()->shouldPreTenure() ? TenuredObject : GenericObject;
 
-    if (templateObject->is<UnboxedArrayObject>()) {
-        uint32_t length = templateObject->as<UnboxedArrayObject>().length();
-        RootedObjectGroup group(cx, templateObject->group());
-        return UnboxedArrayObject::create(cx, group, length, newKind);
-    }
-
     ArrayObject* obj = NewDenseFullyAllocatedArray(cx, templateObject->as<ArrayObject>().length(),
                                                    nullptr, newKind);
     if (!obj)
diff --git a/js/src/vm/JSONParser.cpp b/js/src/vm/JSONParser.cpp
index 01883bb15..e50da3bc4 100644
--- a/js/src/vm/JSONParser.cpp
+++ b/js/src/vm/JSONParser.cpp
@@ -606,8 +606,8 @@ JSONParserBase::finishArray(MutableHandleValue vp, ElementVector& elements)
 {
     MOZ_ASSERT(&elements == &stack.back().elements());
 
-    JSObject* obj = ObjectGroup::newArrayObject(cx, elements.begin(), elements.length(),
-                                                GenericObject);
+    ArrayObject* obj = ObjectGroup::newArrayObject(cx, elements.begin(), elements.length(),
+                                                   GenericObject);
     if (!obj)
         return false;
 
diff --git a/js/src/vm/NativeObject-inl.h b/js/src/vm/NativeObject-inl.h
index 48a42a8db..052a3385c 100644
--- a/js/src/vm/NativeObject-inl.h
+++ b/js/src/vm/NativeObject-inl.h
@@ -235,6 +235,38 @@ NativeObject::ensureDenseElements(ExclusiveContext* cx, uint32_t index, uint32_t
     return DenseElementResult::Success;
 }
 
+inline DenseElementResult
+NativeObject::setOrExtendDenseElements(JSContext* cx, uint32_t start, const Value* vp,
+                                       uint32_t count,
+                                       ShouldUpdateTypes updateTypes)
+{
+    if (denseElementsAreFrozen())
+        return DenseElementResult::Incomplete;
+
+    if (is<ArrayObject>() &&
+        !as<ArrayObject>().lengthIsWritable() &&
+        start + count >= as<ArrayObject>().length())
+    {
+        return DenseElementResult::Incomplete;
+    }
+
+    DenseElementResult result = ensureDenseElements(cx, start, count);
+    if (result != DenseElementResult::Success)
+        return result;
+
+    if (is<ArrayObject>() && start + count >= as<ArrayObject>().length())
+        as<ArrayObject>().setLengthInt32(start + count);
+
+    if (updateTypes == ShouldUpdateTypes::DontUpdate && !shouldConvertDoubleElements()) {
+        copyDenseElements(start, vp, count);
+    } else {
+        for (size_t i = 0; i < count; i++)
+            setDenseElementWithType(cx, start + i, vp[i]);
+    }
+
+    return DenseElementResult::Success;
+}
+
 inline Value
 NativeObject::getDenseOrTypedArrayElement(uint32_t idx)
 {
diff --git a/js/src/vm/NativeObject.cpp b/js/src/vm/NativeObject.cpp
index 21f73f4a9..a3f28653a 100644
--- a/js/src/vm/NativeObject.cpp
+++ b/js/src/vm/NativeObject.cpp
@@ -390,33 +390,6 @@ NativeObject::setLastPropertyMakeNonNative(Shape* shape)
     shape_ = shape;
 }
 
-void
-NativeObject::setLastPropertyMakeNative(ExclusiveContext* cx, Shape* shape)
-{
-    MOZ_ASSERT(getClass()->isNative());
-    MOZ_ASSERT(shape->getObjectClass()->isNative());
-    MOZ_ASSERT(!shape->inDictionary());
-
-    // This method is used to convert unboxed objects into native objects. In
-    // this case, the shape_ field was previously used to store other data and
-    // this should be treated as an initialization.
-    shape_.init(shape);
-
-    slots_ = nullptr;
-    elements_ = emptyObjectElements;
-
-    size_t oldSpan = shape->numFixedSlots();
-    size_t newSpan = shape->slotSpan();
-
-    initializeSlotRange(0, oldSpan);
-
-    // A failure at this point will leave the object as a mutant, and we
-    // can't recover.
-    AutoEnterOOMUnsafeRegion oomUnsafe;
-    if (oldSpan != newSpan && !updateSlotsForSpan(cx, oldSpan, newSpan))
-        oomUnsafe.crash("NativeObject::setLastPropertyMakeNative");
-}
-
 bool
 NativeObject::setSlotSpan(ExclusiveContext* cx, uint32_t span)
 {
diff --git a/js/src/vm/NativeObject.h b/js/src/vm/NativeObject.h
index 4dbc167ab..d9d8b8aec 100644
--- a/js/src/vm/NativeObject.h
+++ b/js/src/vm/NativeObject.h
@@ -339,16 +339,19 @@ IsObjectValueInCompartment(const Value& v, JSCompartment* comp);
 #endif
 
 // Operations which change an object's dense elements can either succeed, fail,
-// or be unable to complete. For native objects, the latter is used when the
-// object's elements must become sparse instead. The enum below is used for
-// such operations, and for similar operations on unboxed arrays and methods
-// that work on both kinds of objects.
+// or be unable to complete. The latter is used when the object's elements must
+// become sparse instead. The enum below is used for such operations.
 enum class DenseElementResult {
     Failure,
     Success,
     Incomplete
 };
 
+enum class ShouldUpdateTypes {
+    Update,
+    DontUpdate
+};
+
 /*
  * NativeObject specifies the internal implementation of a native object.
  *
@@ -467,11 +470,6 @@ class NativeObject : public ShapedObject
     // that are (temporarily) inconsistent.
     void setLastPropertyMakeNonNative(Shape* shape);
 
-    // As for setLastProperty(), but changes the class associated with the
-    // object to a native one. The object's type has already been changed, and
-    // this brings the shape into sync with it.
-    void setLastPropertyMakeNative(ExclusiveContext* cx, Shape* shape);
-
     // Newly-created TypedArrays that map a SharedArrayBuffer are
     // marked as shared by giving them an ObjectElements that has the
     // ObjectElements::SHARED_MEMORY flag set.
@@ -1147,6 +1145,10 @@ class NativeObject : public ShapedObject
         elementsRangeWriteBarrierPost(dstStart, count);
     }
 
+    inline DenseElementResult
+    setOrExtendDenseElements(JSContext* cx, uint32_t start, const Value* vp, uint32_t count,
+                             ShouldUpdateTypes updateTypes = ShouldUpdateTypes::Update);
+
     bool shouldConvertDoubleElements() {
         return getElementsHeader()->shouldConvertDoubleElements();
     }
diff --git a/js/src/vm/ObjectGroup-inl.h b/js/src/vm/ObjectGroup-inl.h
index 9074f4d97..d41343be6 100644
--- a/js/src/vm/ObjectGroup-inl.h
+++ b/js/src/vm/ObjectGroup-inl.h
@@ -108,20 +108,6 @@ ObjectGroup::maybePreliminaryObjects()
     return maybePreliminaryObjectsDontCheckGeneration();
 }
 
-inline UnboxedLayout*
-ObjectGroup::maybeUnboxedLayout()
-{
-    maybeSweep(nullptr);
-    return maybeUnboxedLayoutDontCheckGeneration();
-}
-
-inline UnboxedLayout&
-ObjectGroup::unboxedLayout()
-{
-    maybeSweep(nullptr);
-    return unboxedLayoutDontCheckGeneration();
-}
-
 } // namespace js
 
 #endif /* vm_ObjectGroup_inl_h */
diff --git a/js/src/vm/ObjectGroup.cpp b/js/src/vm/ObjectGroup.cpp
index 46159a972..676792379 100644
--- a/js/src/vm/ObjectGroup.cpp
+++ b/js/src/vm/ObjectGroup.cpp
@@ -18,11 +18,10 @@
 #include "vm/ArrayObject.h"
 #include "vm/Shape.h"
 #include "vm/TaggedProto.h"
-#include "vm/UnboxedObject.h"
 
 #include "jsobjinlines.h"
 
-#include "vm/UnboxedObject-inl.h"
+#include "vm/NativeObject-inl.h"
 
 using namespace js;
 
@@ -56,7 +55,6 @@ ObjectGroup::finalize(FreeOp* fop)
     if (newScriptDontCheckGeneration())
         newScriptDontCheckGeneration()->clear();
     fop->delete_(newScriptDontCheckGeneration());
-    fop->delete_(maybeUnboxedLayoutDontCheckGeneration());
     if (maybePreliminaryObjectsDontCheckGeneration())
         maybePreliminaryObjectsDontCheckGeneration()->clear();
     fop->delete_(maybePreliminaryObjectsDontCheckGeneration());
@@ -83,8 +81,6 @@ ObjectGroup::sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const
     size_t n = 0;
     if (TypeNewScript* newScript = newScriptDontCheckGeneration())
         n += newScript->sizeOfIncludingThis(mallocSizeOf);
-    if (UnboxedLayout* layout = maybeUnboxedLayoutDontCheckGeneration())
-        n += layout->sizeOfIncludingThis(mallocSizeOf);
     return n;
 }
 
@@ -530,8 +526,7 @@ ObjectGroup::defaultNewGroup(ExclusiveContext* cx, const Class* clasp,
     if (p) {
         ObjectGroup* group = p->group;
         MOZ_ASSERT_IF(clasp, group->clasp() == clasp);
-        MOZ_ASSERT_IF(!clasp, group->clasp() == &PlainObject::class_ ||
-                              group->clasp() == &UnboxedPlainObject::class_);
+        MOZ_ASSERT_IF(!clasp, group->clasp() == &PlainObject::class_);
         MOZ_ASSERT(group->proto() == proto);
         return group;
     }
@@ -774,7 +769,7 @@ GetValueTypeForTable(const Value& v)
     return type;
 }
 
-/* static */ JSObject*
+/* static */ ArrayObject*
 ObjectGroup::newArrayObject(ExclusiveContext* cx,
                             const Value* vp, size_t length,
                             NewObjectKind newKind, NewArrayKind arrayKind)
@@ -838,56 +833,13 @@ ObjectGroup::newArrayObject(ExclusiveContext* cx,
 
         AddTypePropertyId(cx, group, nullptr, JSID_VOID, elementType);
 
-        if (elementType != TypeSet::UnknownType()) {
-            // Keep track of the initial objects we create with this type.
-            // If the initial ones have a consistent shape and property types, we
-            // will try to use an unboxed layout for the group.
-            PreliminaryObjectArrayWithTemplate* preliminaryObjects =
-                cx->new_<PreliminaryObjectArrayWithTemplate>(nullptr);
-            if (!preliminaryObjects)
-                return nullptr;
-            group->setPreliminaryObjects(preliminaryObjects);
-        }
-
         if (!p.add(cx, *table, ObjectGroupCompartment::ArrayObjectKey(elementType), group))
             return nullptr;
     }
 
     // The type of the elements being added will already be reflected in type
-    // information, but make sure when creating an unboxed array that the
-    // common element type is suitable for the unboxed representation.
+    // information.
     ShouldUpdateTypes updateTypes = ShouldUpdateTypes::DontUpdate;
-    if (!MaybeAnalyzeBeforeCreatingLargeArray(cx, group, vp, length))
-        return nullptr;
-    if (group->maybePreliminaryObjects())
-        group->maybePreliminaryObjects()->maybeAnalyze(cx, group);
-    if (group->maybeUnboxedLayout()) {
-        switch (group->unboxedLayout().elementType()) {
-          case JSVAL_TYPE_BOOLEAN:
-            if (elementType != TypeSet::BooleanType())
-                updateTypes = ShouldUpdateTypes::Update;
-            break;
-          case JSVAL_TYPE_INT32:
-            if (elementType != TypeSet::Int32Type())
-                updateTypes = ShouldUpdateTypes::Update;
-            break;
-          case JSVAL_TYPE_DOUBLE:
-            if (elementType != TypeSet::Int32Type() && elementType != TypeSet::DoubleType())
-                updateTypes = ShouldUpdateTypes::Update;
-            break;
-          case JSVAL_TYPE_STRING:
-            if (elementType != TypeSet::StringType())
-                updateTypes = ShouldUpdateTypes::Update;
-            break;
-          case JSVAL_TYPE_OBJECT:
-            if (elementType != TypeSet::NullType() && !elementType.get().isObjectUnchecked())
-                updateTypes = ShouldUpdateTypes::Update;
-            break;
-          default:
-            MOZ_CRASH();
-        }
-    }
-
     return NewCopiedArrayTryUseGroup(cx, group, vp, length, newKind, updateTypes);
 }
 
@@ -897,49 +849,15 @@ GiveObjectGroup(ExclusiveContext* cx, JSObject* source, JSObject* target)
 {
     MOZ_ASSERT(source->group() != target->group());
 
-    if (!target->is<ArrayObject>() && !target->is<UnboxedArrayObject>())
-        return true;
-
-    if (target->group()->maybePreliminaryObjects()) {
-        bool force = IsInsideNursery(source);
-        target->group()->maybePreliminaryObjects()->maybeAnalyze(cx, target->group(), force);
-    }
-
-    if (target->is<ArrayObject>()) {
-        ObjectGroup* sourceGroup = source->group();
-
-        if (source->is<UnboxedArrayObject>()) {
-            Shape* shape = target->as<ArrayObject>().lastProperty();
-            if (!UnboxedArrayObject::convertToNativeWithGroup(cx, source, target->group(), shape))
-                return false;
-        } else if (source->is<ArrayObject>()) {
-            source->setGroup(target->group());
-        } else {
-            return true;
-        }
-
-        if (sourceGroup->maybePreliminaryObjects())
-            sourceGroup->maybePreliminaryObjects()->unregisterObject(source);
-        if (target->group()->maybePreliminaryObjects())
-            target->group()->maybePreliminaryObjects()->registerNewObject(source);
-
-        for (size_t i = 0; i < source->as<ArrayObject>().getDenseInitializedLength(); i++) {
-            Value v = source->as<ArrayObject>().getDenseElement(i);
-            AddTypePropertyId(cx, source->group(), source, JSID_VOID, v);
-        }
-
+    if (!target->is<ArrayObject>() || !source->is<ArrayObject>()) {
         return true;
     }
 
-    if (target->is<UnboxedArrayObject>()) {
-        if (!source->is<UnboxedArrayObject>())
-            return true;
-        if (source->as<UnboxedArrayObject>().elementType() != JSVAL_TYPE_INT32)
-            return true;
-        if (target->as<UnboxedArrayObject>().elementType() != JSVAL_TYPE_DOUBLE)
-            return true;
+    source->setGroup(target->group());
 
-        return source->as<UnboxedArrayObject>().convertInt32ToDouble(cx, target->group());
+    for (size_t i = 0; i < source->as<ArrayObject>().getDenseInitializedLength(); i++) {
+        Value v = source->as<ArrayObject>().getDenseElement(i);
+        AddTypePropertyId(cx, source->group(), source, JSID_VOID, v);
     }
 
     return true;
@@ -1048,46 +966,6 @@ js::CombinePlainObjectPropertyTypes(ExclusiveContext* cx, JSObject* newObj,
                 }
             }
         }
-    } else if (newObj->is<UnboxedPlainObject>()) {
-        const UnboxedLayout& layout = newObj->as<UnboxedPlainObject>().layout();
-        const int32_t* traceList = layout.traceList();
-        if (!traceList)
-            return true;
-
-        uint8_t* newData = newObj->as<UnboxedPlainObject>().data();
-        uint8_t* oldData = oldObj->as<UnboxedPlainObject>().data();
-
-        for (; *traceList != -1; traceList++) {}
-        traceList++;
-        for (; *traceList != -1; traceList++) {
-            JSObject* newInnerObj = *reinterpret_cast<JSObject**>(newData + *traceList);
-            JSObject* oldInnerObj = *reinterpret_cast<JSObject**>(oldData + *traceList);
-
-            if (!newInnerObj || !oldInnerObj || SameGroup(oldInnerObj, newInnerObj))
-                continue;
-
-            if (!GiveObjectGroup(cx, newInnerObj, oldInnerObj))
-                return false;
-
-            if (SameGroup(oldInnerObj, newInnerObj))
-                continue;
-
-            if (!GiveObjectGroup(cx, oldInnerObj, newInnerObj))
-                return false;
-
-            if (SameGroup(oldInnerObj, newInnerObj)) {
-                for (size_t i = 1; i < ncompare; i++) {
-                    if (compare[i].isObject() && SameGroup(&compare[i].toObject(), newObj)) {
-                        uint8_t* otherData = compare[i].toObject().as<UnboxedPlainObject>().data();
-                        JSObject* otherInnerObj = *reinterpret_cast<JSObject**>(otherData + *traceList);
-                        if (otherInnerObj && !SameGroup(otherInnerObj, newInnerObj)) {
-                            if (!GiveObjectGroup(cx, otherInnerObj, newInnerObj))
-                                return false;
-                        }
-                    }
-                }
-            }
-        }
     }
 
     return true;
@@ -1311,12 +1189,6 @@ ObjectGroup::newPlainObject(ExclusiveContext* cx, IdValuePair* properties, size_
 
     RootedObjectGroup group(cx, p->value().group);
 
-    // Watch for existing groups which now use an unboxed layout.
-    if (group->maybeUnboxedLayout()) {
-        MOZ_ASSERT(group->unboxedLayout().properties().length() == nproperties);
-        return UnboxedPlainObject::createWithProperties(cx, group, newKind, properties);
-    }
-
     // Update property types according to the properties we are about to add.
     // Do this before we do anything which can GC, which might move or remove
     // this table entry.
@@ -1503,18 +1375,6 @@ ObjectGroup::allocationSiteGroup(JSContext* cx, JSScript* scriptArg, jsbytecode*
         }
     }
 
-    if (kind == JSProto_Array &&
-        (JSOp(*pc) == JSOP_NEWARRAY || IsCallPC(pc)) &&
-        cx->options().unboxedArrays())
-    {
-        PreliminaryObjectArrayWithTemplate* preliminaryObjects =
-            cx->new_<PreliminaryObjectArrayWithTemplate>(nullptr);
-        if (preliminaryObjects)
-            res->setPreliminaryObjects(preliminaryObjects);
-        else
-            cx->recoverFromOutOfMemory();
-    }
-
     if (!table->add(p, key, res)) {
         ReportOutOfMemory(cx);
         return nullptr;
diff --git a/js/src/vm/ObjectGroup.h b/js/src/vm/ObjectGroup.h
index 4e24de9f1..0b6eaee51 100644
--- a/js/src/vm/ObjectGroup.h
+++ b/js/src/vm/ObjectGroup.h
@@ -20,7 +20,6 @@
 namespace js {
 
 class TypeDescr;
-class UnboxedLayout;
 
 class PreliminaryObjectArrayWithTemplate;
 class TypeNewScript;
@@ -154,16 +153,6 @@ class ObjectGroup : public gc::TenuredCell
         // For some plain objects, the addendum stores a PreliminaryObjectArrayWithTemplate.
         Addendum_PreliminaryObjects,
 
-        // When objects in this group have an unboxed representation, the
-        // addendum stores an UnboxedLayout (which might have a TypeNewScript
-        // as well, if the group is also constructed using 'new').
-        Addendum_UnboxedLayout,
-
-        // If this group is used by objects that have been converted from an
-        // unboxed representation and/or have the same allocation kind as such
-        // objects, the addendum points to that unboxed group.
-        Addendum_OriginalUnboxedGroup,
-
         // When used by typed objects, the addendum stores a TypeDescr.
         Addendum_TypeDescr
     };
@@ -185,7 +174,6 @@ class ObjectGroup : public gc::TenuredCell
         return nullptr;
     }
 
-    TypeNewScript* anyNewScript();
     void detachNewScript(bool writeBarrier, ObjectGroup* replacement);
 
     ObjectGroupFlags flagsDontCheckGeneration() const {
@@ -225,34 +213,6 @@ class ObjectGroup : public gc::TenuredCell
                maybePreliminaryObjectsDontCheckGeneration();
     }
 
-    inline UnboxedLayout* maybeUnboxedLayout();
-    inline UnboxedLayout& unboxedLayout();
-
-    UnboxedLayout* maybeUnboxedLayoutDontCheckGeneration() const {
-        if (addendumKind() == Addendum_UnboxedLayout)
-            return reinterpret_cast<UnboxedLayout*>(addendum_);
-        return nullptr;
-    }
-
-    UnboxedLayout& unboxedLayoutDontCheckGeneration() const {
-        MOZ_ASSERT(addendumKind() == Addendum_UnboxedLayout);
-        return *maybeUnboxedLayoutDontCheckGeneration();
-    }
-
-    void setUnboxedLayout(UnboxedLayout* layout) {
-        setAddendum(Addendum_UnboxedLayout, layout);
-    }
-
-    ObjectGroup* maybeOriginalUnboxedGroup() const {
-        if (addendumKind() == Addendum_OriginalUnboxedGroup)
-            return reinterpret_cast<ObjectGroup*>(addendum_);
-        return nullptr;
-    }
-
-    void setOriginalUnboxedGroup(ObjectGroup* group) {
-        setAddendum(Addendum_OriginalUnboxedGroup, group);
-    }
-
     TypeDescr* maybeTypeDescr() {
         // Note: there is no need to sweep when accessing the type descriptor
         // of an object, as it is strongly held and immutable.
@@ -313,9 +273,8 @@ class ObjectGroup : public gc::TenuredCell
      * that can be read out of that property in actual JS objects. In native
      * objects, property types account for plain data properties (those with a
      * slot and no getter or setter hook) and dense elements. In typed objects
-     * and unboxed objects, property types account for object and value
-     * properties and elements in the object, and expando properties in unboxed
-     * objects.
+     * property types account for object and value properties and elements in
+     * the object.
      *
      * For accesses on these properties, the correspondence is as follows:
      *
@@ -338,10 +297,9 @@ class ObjectGroup : public gc::TenuredCell
      * 2. Array lengths are special cased by the compiler and VM and are not
      *    reflected in property types.
      *
-     * 3. In typed objects (but not unboxed objects), the initial values of
-     *    properties (null pointers and undefined values) are not reflected in
-     *    the property types. These values are always possible when reading the
-     *    property.
+     * 3. In typed objects, the initial values of properties (null pointers and
+     *    undefined values) are not reflected in the property types. These
+     *    values are always possible when reading the property.
      *
      * We establish these by using write barriers on calls to setProperty and
      * defineProperty which are on native properties, and on any jitcode which
@@ -455,12 +413,6 @@ class ObjectGroup : public gc::TenuredCell
         return &flags_;
     }
 
-    // Get the bit pattern stored in an object's addendum when it has an
-    // original unboxed group.
-    static inline int32_t addendumOriginalUnboxedGroupValue() {
-        return Addendum_OriginalUnboxedGroup << OBJECT_FLAG_ADDENDUM_SHIFT;
-    }
-
     inline uint32_t basePropertyCount();
 
   private:
@@ -505,14 +457,14 @@ class ObjectGroup : public gc::TenuredCell
         UnknownIndex  // Make an array with an unknown element type.
     };
 
-    // Create an ArrayObject or UnboxedArrayObject with the specified elements
-    // and a group specialized for the elements.
-    static JSObject* newArrayObject(ExclusiveContext* cx, const Value* vp, size_t length,
-                                    NewObjectKind newKind,
-                                    NewArrayKind arrayKind = NewArrayKind::Normal);
+    // Create an ArrayObject with the specified elements and a group specialized
+    // for the elements.
+    static ArrayObject* newArrayObject(ExclusiveContext* cx, const Value* vp, size_t length,
+                                       NewObjectKind newKind,
+                                       NewArrayKind arrayKind = NewArrayKind::Normal);
 
-    // Create a PlainObject or UnboxedPlainObject with the specified properties
-    // and a group specialized for those properties.
+    // Create a PlainObject with the specified properties and a group specialized
+    // for those properties.
     static JSObject* newPlainObject(ExclusiveContext* cx,
                                     IdValuePair* properties, size_t nproperties,
                                     NewObjectKind newKind);
diff --git a/js/src/vm/Opcodes.h b/js/src/vm/Opcodes.h
index 4b044c8d8..095ef57ae 100644
--- a/js/src/vm/Opcodes.h
+++ b/js/src/vm/Opcodes.h
@@ -1281,17 +1281,7 @@
      *   Stack: receiver, obj, propval => obj[propval]
      */ \
     macro(JSOP_GETELEM_SUPER, 125, "getelem-super", NULL, 1,  3,  1, JOF_BYTE |JOF_ELEM|JOF_LEFTASSOC) \
-    /*
-     * Pushes newly created array for a spread call onto the stack. This has
-     * the same semantics as JSOP_NEWARRAY, but is distinguished to avoid
-     * using unboxed arrays in spread calls, which would make compiling spread
-     * calls in baseline more complex.
-     *   Category: Literals
-     *   Type: Array
-     *   Operands: uint32_t length
-     *   Stack: => obj
-     */ \
-    macro(JSOP_SPREADCALLARRAY, 126, "spreadcallarray", NULL, 5,  0,  1, JOF_UINT32) \
+    macro(JSOP_UNUSED126, 126, "unused126", NULL, 5,  0,  1, JOF_UINT32) \
     \
     /*
      * Defines the given function on the current scope.
diff --git a/js/src/vm/ReceiverGuard.cpp b/js/src/vm/ReceiverGuard.cpp
index 97df908c3..e95e8a208 100644
--- a/js/src/vm/ReceiverGuard.cpp
+++ b/js/src/vm/ReceiverGuard.cpp
@@ -7,7 +7,6 @@
 #include "vm/ReceiverGuard.h"
 
 #include "builtin/TypedObject.h"
-#include "vm/UnboxedObject.h"
 #include "jsobjinlines.h"
 
 using namespace js;
@@ -16,11 +15,7 @@ ReceiverGuard::ReceiverGuard(JSObject* obj)
   : group(nullptr), shape(nullptr)
 {
     if (obj) {
-        if (obj->is<UnboxedPlainObject>()) {
-            group = obj->group();
-            if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando())
-                shape = expando->lastProperty();
-        } else if (obj->is<UnboxedArrayObject>() || obj->is<TypedObject>()) {
+        if (obj->is<TypedObject>()) {
             group = obj->group();
         } else {
             shape = obj->maybeShape();
@@ -33,9 +28,7 @@ ReceiverGuard::ReceiverGuard(ObjectGroup* group, Shape* shape)
 {
     if (group) {
         const Class* clasp = group->clasp();
-        if (clasp == &UnboxedPlainObject::class_) {
-            // Keep both group and shape.
-        } else if (clasp == &UnboxedArrayObject::class_ || IsTypedObjectClass(clasp)) {
+        if (IsTypedObjectClass(clasp)) {
             this->shape = nullptr;
         } else {
             this->group = nullptr;
@@ -46,12 +39,8 @@ ReceiverGuard::ReceiverGuard(ObjectGroup* group, Shape* shape)
 /* static */ int32_t
 HeapReceiverGuard::keyBits(JSObject* obj)
 {
-    if (obj->is<UnboxedPlainObject>()) {
-        // Both the group and shape need to be guarded for unboxed plain objects.
-        return obj->as<UnboxedPlainObject>().maybeExpando() ? 0 : 1;
-    }
-    if (obj->is<UnboxedArrayObject>() || obj->is<TypedObject>()) {
-        // Only the group needs to be guarded for unboxed arrays and typed objects.
+    if (obj->is<TypedObject>()) {
+        // Only the group needs to be guarded for typed objects.
         return 2;
     }
     // Other objects only need the shape to be guarded.
diff --git a/js/src/vm/ReceiverGuard.h b/js/src/vm/ReceiverGuard.h
index 459cc0012..c14f0d83b 100644
--- a/js/src/vm/ReceiverGuard.h
+++ b/js/src/vm/ReceiverGuard.h
@@ -28,11 +28,6 @@ namespace js {
 // TypedObject: The structure of a typed object is determined by its group.
 //   All typed objects with the same group have the same class, prototype, and
 //   own properties.
-//
-// UnboxedPlainObject: The structure of an unboxed plain object is determined
-//   by its group and its expando object's shape, if there is one. All unboxed
-//   plain objects with the same group and expando shape have the same
-//   properties except those stored in the expando's dense elements.
 
 class HeapReceiverGuard;
 class RootedReceiverGuard;
diff --git a/js/src/vm/Runtime.cpp b/js/src/vm/Runtime.cpp
index 8eb997c71..5fc8e0e17 100644
--- a/js/src/vm/Runtime.cpp
+++ b/js/src/vm/Runtime.cpp
@@ -589,7 +589,7 @@ JSRuntime::requestInterrupt(InterruptMode mode)
         // Atomics.wait().
         fx.lock();
         if (fx.isWaiting())
-            fx.wake(FutexRuntime::WakeForJSInterrupt);
+            fx.notify(FutexRuntime::NotifyForJSInterrupt);
         fx.unlock();
         InterruptRunningJitCode(this);
     }
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 328a960b6..ccd4cc8d7 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -2200,8 +2200,10 @@ static const JSFunctionSpec intrinsic_functions[] = {
     JS_INLINABLE_FN("std_String_charAt",         str_charAt,                   1,0, StringCharAt),
     JS_FN("std_String_endsWith",                 str_endsWith,                 1,0),
     JS_FN("std_String_trim",                     str_trim,                     0,0),
-    JS_FN("std_String_trimLeft",                 str_trimLeft,                 0,0),
-    JS_FN("std_String_trimRight",                str_trimRight,                0,0),
+    JS_FN("std_String_trimLeft",                 str_trimStart,                0,0),
+    JS_FN("std_String_trimStart",                str_trimStart,                0,0),
+    JS_FN("std_String_trimRight",                str_trimEnd,                  0,0),
+    JS_FN("std_String_trimEnd",                  str_trimEnd,                  0,0),
     JS_FN("std_String_toLocaleLowerCase",        str_toLocaleLowerCase,        0,0),
     JS_FN("std_String_toLocaleUpperCase",        str_toLocaleUpperCase,        0,0),
     JS_FN("std_String_normalize",                str_normalize,                0,0),
diff --git a/js/src/vm/Stack.cpp b/js/src/vm/Stack.cpp
index 87e95c893..c5f2cf5f3 100644
--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -82,7 +82,7 @@ InterpreterFrame::isNonGlobalEvalFrame() const
     return isEvalFrame() && script()->bodyScope()->as<EvalScope>().isNonGlobal();
 }
 
-JSObject*
+ArrayObject*
 InterpreterFrame::createRestParameter(JSContext* cx)
 {
     MOZ_ASSERT(script()->hasRest());
diff --git a/js/src/vm/Stack.h b/js/src/vm/Stack.h
index 552738d89..dc9306c99 100644
--- a/js/src/vm/Stack.h
+++ b/js/src/vm/Stack.h
@@ -523,7 +523,7 @@ class InterpreterFrame
     ArgumentsObject& argsObj() const;
     void initArgsObj(ArgumentsObject& argsobj);
 
-    JSObject* createRestParameter(JSContext* cx);
+    ArrayObject* createRestParameter(JSContext* cx);
 
     /*
      * Environment chain
diff --git a/js/src/vm/TypeInference-inl.h b/js/src/vm/TypeInference-inl.h
index da47fa898..2af252cea 100644
--- a/js/src/vm/TypeInference-inl.h
+++ b/js/src/vm/TypeInference-inl.h
@@ -23,7 +23,6 @@
 #include "vm/SharedArrayObject.h"
 #include "vm/StringObject.h"
 #include "vm/TypedArrayObject.h"
-#include "vm/UnboxedObject.h"
 
 #include "jscntxtinlines.h"
 
@@ -285,10 +284,6 @@ TypeIdString(jsid id)
  */
 struct AutoEnterAnalysis
 {
-    // For use when initializing an UnboxedLayout.  The UniquePtr's destructor
-    // must run when GC is not suppressed.
-    UniquePtr<UnboxedLayout> unboxedLayoutToCleanUp;
-
     // Prevent GC activity in the middle of analysis.
     gc::AutoSuppressGC suppressGC;
 
diff --git a/js/src/vm/TypeInference.cpp b/js/src/vm/TypeInference.cpp
index 4775a2dea..ba809fc4e 100644
--- a/js/src/vm/TypeInference.cpp
+++ b/js/src/vm/TypeInference.cpp
@@ -35,7 +35,6 @@
 #include "vm/Opcodes.h"
 #include "vm/Shape.h"
 #include "vm/Time.h"
-#include "vm/UnboxedObject.h"
 
 #include "jsatominlines.h"
 #include "jsscriptinlines.h"
@@ -297,9 +296,6 @@ js::ObjectGroupHasProperty(JSContext* cx, ObjectGroup* group, jsid id, const Val
                         return true;
                 }
             }
-            JSObject* obj = &value.toObject();
-            if (!obj->hasLazyGroup() && obj->group()->maybeOriginalUnboxedGroup())
-                return true;
         }
 
         if (!types->hasType(type)) {
@@ -1944,33 +1940,6 @@ class ConstraintDataFreezeObjectForTypedArrayData
     }
 };
 
-// Constraint which triggers recompilation if an unboxed object in some group
-// is converted to a native object.
-class ConstraintDataFreezeObjectForUnboxedConvertedToNative
-{
-  public:
-    ConstraintDataFreezeObjectForUnboxedConvertedToNative()
-    {}
-
-    const char* kind() { return "freezeObjectForUnboxedConvertedToNative"; }
-
-    bool invalidateOnNewType(TypeSet::Type type) { return false; }
-    bool invalidateOnNewPropertyState(TypeSet* property) { return false; }
-    bool invalidateOnNewObjectState(ObjectGroup* group) {
-        return group->unboxedLayout().nativeGroup() != nullptr;
-    }
-
-    bool constraintHolds(JSContext* cx,
-                         const HeapTypeSetKey& property, TemporaryTypeSet* expected)
-    {
-        return !invalidateOnNewObjectState(property.object()->maybeGroup());
-    }
-
-    bool shouldSweep() { return false; }
-
-    JSCompartment* maybeCompartment() { return nullptr; }
-};
-
 } /* anonymous namespace */
 
 void
@@ -1995,17 +1964,6 @@ TypeSet::ObjectKey::watchStateChangeForTypedArrayData(CompilerConstraintList* co
                                     ConstraintDataFreezeObjectForTypedArrayData(tarray)));
 }
 
-void
-TypeSet::ObjectKey::watchStateChangeForUnboxedConvertedToNative(CompilerConstraintList* constraints)
-{
-    HeapTypeSetKey objectProperty = property(JSID_EMPTY);
-    LifoAlloc* alloc = constraints->alloc();
-
-    typedef CompilerConstraintInstance<ConstraintDataFreezeObjectForUnboxedConvertedToNative> T;
-    constraints->add(alloc->new_<T>(alloc, objectProperty,
-                                    ConstraintDataFreezeObjectForUnboxedConvertedToNative()));
-}
-
 static void
 ObjectStateChange(ExclusiveContext* cxArg, ObjectGroup* group, bool markingUnknown)
 {
@@ -2516,8 +2474,6 @@ TemporaryTypeSet::propertyNeedsBarrier(CompilerConstraintList* constraints, jsid
 bool
 js::ClassCanHaveExtraProperties(const Class* clasp)
 {
-    if (clasp == &UnboxedPlainObject::class_ || clasp == &UnboxedArrayObject::class_)
-        return false;
     return clasp->getResolve()
         || clasp->getOpsLookupProperty()
         || clasp->getOpsGetProperty()
@@ -2816,15 +2772,6 @@ js::AddTypePropertyId(ExclusiveContext* cx, ObjectGroup* group, JSObject* obj, j
     // from acquiring the fully initialized group.
     if (group->newScript() && group->newScript()->initializedGroup())
         AddTypePropertyId(cx, group->newScript()->initializedGroup(), nullptr, id, type);
-
-    // Maintain equivalent type information for unboxed object groups and their
-    // corresponding native group. Since type sets might contain the unboxed
-    // group but not the native group, this ensures optimizations based on the
-    // unboxed group are valid for the native group.
-    if (group->maybeUnboxedLayout() && group->maybeUnboxedLayout()->nativeGroup())
-        AddTypePropertyId(cx, group->maybeUnboxedLayout()->nativeGroup(), nullptr, id, type);
-    if (ObjectGroup* unboxedGroup = group->maybeOriginalUnboxedGroup())
-        AddTypePropertyId(cx, unboxedGroup, nullptr, id, type);
 }
 
 void
@@ -2896,12 +2843,6 @@ ObjectGroup::setFlags(ExclusiveContext* cx, ObjectGroupFlags flags)
     // acquired properties analysis.
     if (newScript() && newScript()->initializedGroup())
         newScript()->initializedGroup()->setFlags(cx, flags);
-
-    // Propagate flag changes between unboxed and corresponding native groups.
-    if (maybeUnboxedLayout() && maybeUnboxedLayout()->nativeGroup())
-        maybeUnboxedLayout()->nativeGroup()->setFlags(cx, flags);
-    if (ObjectGroup* unboxedGroup = maybeOriginalUnboxedGroup())
-        unboxedGroup->setFlags(cx, flags);
 }
 
 void
@@ -2934,23 +2875,6 @@ ObjectGroup::markUnknown(ExclusiveContext* cx)
             prop->types.setNonDataProperty(cx);
         }
     }
-
-    if (ObjectGroup* unboxedGroup = maybeOriginalUnboxedGroup())
-        MarkObjectGroupUnknownProperties(cx, unboxedGroup);
-    if (maybeUnboxedLayout() && maybeUnboxedLayout()->nativeGroup())
-        MarkObjectGroupUnknownProperties(cx, maybeUnboxedLayout()->nativeGroup());
-    if (ObjectGroup* unboxedGroup = maybeOriginalUnboxedGroup())
-        MarkObjectGroupUnknownProperties(cx, unboxedGroup);
-}
-
-TypeNewScript*
-ObjectGroup::anyNewScript()
-{
-    if (newScript())
-        return newScript();
-    if (maybeUnboxedLayout())
-        return unboxedLayout().newScript();
-    return nullptr;
 }
 
 void
@@ -2960,7 +2884,7 @@ ObjectGroup::detachNewScript(bool writeBarrier, ObjectGroup* replacement)
     // analyzed, remove it from the newObjectGroups table so that it will not be
     // produced by calling 'new' on the associated function anymore.
     // The TypeNewScript is not actually destroyed.
-    TypeNewScript* newScript = anyNewScript();
+    TypeNewScript* newScript = this->newScript();
     MOZ_ASSERT(newScript);
 
     if (newScript->analyzed()) {
@@ -2979,10 +2903,7 @@ ObjectGroup::detachNewScript(bool writeBarrier, ObjectGroup* replacement)
         MOZ_ASSERT(!replacement);
     }
 
-    if (this->newScript())
-        setAddendum(Addendum_None, nullptr, writeBarrier);
-    else
-        unboxedLayout().setNewScript(nullptr, writeBarrier);
+    setAddendum(Addendum_None, nullptr, writeBarrier);
 }
 
 void
@@ -2993,7 +2914,7 @@ ObjectGroup::maybeClearNewScriptOnOOM()
     if (!isMarked())
         return;
 
-    TypeNewScript* newScript = anyNewScript();
+    TypeNewScript* newScript = this->newScript();
     if (!newScript)
         return;
 
@@ -3008,7 +2929,7 @@ ObjectGroup::maybeClearNewScriptOnOOM()
 void
 ObjectGroup::clearNewScript(ExclusiveContext* cx, ObjectGroup* replacement /* = nullptr*/)
 {
-    TypeNewScript* newScript = anyNewScript();
+    TypeNewScript* newScript = this->newScript();
     if (!newScript)
         return;
 
@@ -3404,7 +3325,7 @@ JSFunction::setTypeForScriptedFunction(ExclusiveContext* cx, HandleFunction fun,
 /////////////////////////////////////////////////////////////////////
 
 void
-PreliminaryObjectArray::registerNewObject(JSObject* res)
+PreliminaryObjectArray::registerNewObject(PlainObject* res)
 {
     // The preliminary object pointers are weak, and won't be swept properly
     // during nursery collections, so the preliminary objects need to be
@@ -3422,7 +3343,7 @@ PreliminaryObjectArray::registerNewObject(JSObject* res)
 }
 
 void
-PreliminaryObjectArray::unregisterObject(JSObject* obj)
+PreliminaryObjectArray::unregisterObject(PlainObject* obj)
 {
     for (size_t i = 0; i < COUNT; i++) {
         if (objects[i] == obj) {
@@ -3462,22 +3383,6 @@ PreliminaryObjectArray::sweep()
     for (size_t i = 0; i < COUNT; i++) {
         JSObject** ptr = &objects[i];
         if (*ptr && IsAboutToBeFinalizedUnbarriered(ptr)) {
-            // Before we clear this reference, change the object's group to the
-            // Object.prototype group. This is done to ensure JSObject::finalize
-            // sees a NativeObject Class even if we change the current group's
-            // Class to one of the unboxed object classes in the meantime. If
-            // the compartment's global is dead, we don't do anything as the
-            // group's Class is not going to change in that case.
-            JSObject* obj = *ptr;
-            GlobalObject* global = obj->compartment()->unsafeUnbarrieredMaybeGlobal();
-            if (global && !obj->isSingleton()) {
-                JSObject* objectProto = GetBuiltinPrototypePure(global, JSProto_Object);
-                obj->setGroup(objectProto->groupRaw());
-                MOZ_ASSERT(obj->is<NativeObject>());
-                MOZ_ASSERT(obj->getClass() == objectProto->getClass());
-                MOZ_ASSERT(!obj->getClass()->hasFinalize());
-            }
-
             *ptr = nullptr;
         }
     }
@@ -3577,17 +3482,11 @@ PreliminaryObjectArrayWithTemplate::maybeAnalyze(ExclusiveContext* cx, ObjectGro
         }
     }
 
-    TryConvertToUnboxedLayout(cx, enter, shape(), group, preliminaryObjects);
-    if (group->maybeUnboxedLayout())
-        return;
-
-    if (shape()) {
-        // We weren't able to use an unboxed layout, but since the preliminary
-        // objects still reflect the template object's properties, and all
-        // objects in the future will be created with those properties, the
-        // properties can be marked as definite for objects in the group.
-        group->addDefiniteProperties(cx, shape());
-    }
+    // Since the preliminary objects still reflect the template object's
+    // properties, and all objects in the future will be created with those
+    // properties, the properties can be marked as definitive for objects in
+    // the group.
+    group->addDefiniteProperties(cx, shape());
 }
 
 /////////////////////////////////////////////////////////////////////
@@ -3601,7 +3500,6 @@ TypeNewScript::make(JSContext* cx, ObjectGroup* group, JSFunction* fun)
 {
     MOZ_ASSERT(cx->zone()->types.activeAnalysis);
     MOZ_ASSERT(!group->newScript());
-    MOZ_ASSERT(!group->maybeUnboxedLayout());
 
     // rollbackPartiallyInitializedObjects expects function_ to be
     // canonicalized.
@@ -3861,34 +3759,9 @@ TypeNewScript::maybeAnalyze(JSContext* cx, ObjectGroup* group, bool* regenerate,
         PodCopy(initializerList, initializerVector.begin(), initializerVector.length());
     }
 
-    // Try to use an unboxed representation for the group.
-    if (!TryConvertToUnboxedLayout(cx, enter, templateObject()->lastProperty(), group, preliminaryObjects))
-        return false;
-
     js_delete(preliminaryObjects);
     preliminaryObjects = nullptr;
 
-    if (group->maybeUnboxedLayout()) {
-        // An unboxed layout was constructed for the group, and this has already
-        // been hooked into it.
-        MOZ_ASSERT(group->unboxedLayout().newScript() == this);
-        destroyNewScript.group = nullptr;
-
-        // Clear out the template object, which is not used for TypeNewScripts
-        // with an unboxed layout. Currently it is a mutant object with a
-        // non-native group and native shape, so make it safe for GC by changing
-        // its group to the default for its prototype.
-        AutoEnterOOMUnsafeRegion oomUnsafe;
-        ObjectGroup* plainGroup = ObjectGroup::defaultNewGroup(cx, &PlainObject::class_,
-                                                               group->proto());
-        if (!plainGroup)
-            oomUnsafe.crash("TypeNewScript::maybeAnalyze");
-        templateObject_->setGroup(plainGroup);
-        templateObject_ = nullptr;
-
-        return true;
-    }
-
     if (prefixShape->slotSpan() == templateObject()->slotSpan()) {
         // The definite properties analysis found exactly the properties that
         // are held in common by the preliminary objects. No further analysis
@@ -3984,12 +3857,6 @@ TypeNewScript::rollbackPartiallyInitializedObjects(JSContext* cx, ObjectGroup* g
             continue;
         }
 
-        if (thisv.toObject().is<UnboxedPlainObject>()) {
-            AutoEnterOOMUnsafeRegion oomUnsafe;
-            if (!UnboxedPlainObject::convertToNative(cx, &thisv.toObject()))
-                oomUnsafe.crash("rollbackPartiallyInitializedObjects");
-        }
-
         // Found a matching frame.
         RootedPlainObject obj(cx, &thisv.toObject().as<PlainObject>());
 
@@ -4183,12 +4050,6 @@ ConstraintTypeSet::sweep(Zone* zone, AutoClearTypeInferenceStateOnOOM& oom)
                 // Object sets containing objects with unknown properties might
                 // not be complete. Mark the type set as unknown, which it will
                 // be treated as during Ion compilation.
-                //
-                // Note that we don't have to do this when the type set might
-                // be missing the native group corresponding to an unboxed
-                // object group. In this case, the native group points to the
-                // unboxed object group via its addendum, so as long as objects
-                // with either group exist, neither group will be finalized.
                 flags |= TYPE_FLAG_ANYOBJECT;
                 clearObjects();
                 objectCount = 0;
@@ -4272,21 +4133,6 @@ ObjectGroup::sweep(AutoClearTypeInferenceStateOnOOM* oom)
     Maybe<AutoClearTypeInferenceStateOnOOM> fallbackOOM;
     EnsureHasAutoClearTypeInferenceStateOnOOM(oom, zone(), fallbackOOM);
 
-    if (maybeUnboxedLayout()) {
-        // Remove unboxed layouts that are about to be finalized from the
-        // compartment wide list while we are still on the main thread.
-        ObjectGroup* group = this;
-        if (IsAboutToBeFinalizedUnbarriered(&group))
-            unboxedLayout().detachFromCompartment();
-
-        if (unboxedLayout().newScript())
-            unboxedLayout().newScript()->sweep();
-
-        // Discard constructor code to avoid holding onto ExecutablePools.
-        if (zone()->isGCCompacting())
-            unboxedLayout().setConstructorCode(nullptr);
-    }
-
     if (maybePreliminaryObjects())
         maybePreliminaryObjects()->sweep();
 
diff --git a/js/src/vm/TypeInference.h b/js/src/vm/TypeInference.h
index 0f1cd4936..94ce7e871 100644
--- a/js/src/vm/TypeInference.h
+++ b/js/src/vm/TypeInference.h
@@ -262,7 +262,6 @@ class TypeSet
         bool hasStableClassAndProto(CompilerConstraintList* constraints);
         void watchStateChangeForInlinedCall(CompilerConstraintList* constraints);
         void watchStateChangeForTypedArrayData(CompilerConstraintList* constraints);
-        void watchStateChangeForUnboxedConvertedToNative(CompilerConstraintList* constraints);
         HeapTypeSetKey property(jsid id);
         void ensureTrackedProperty(JSContext* cx, jsid id);
 
@@ -815,8 +814,8 @@ class PreliminaryObjectArray
   public:
     PreliminaryObjectArray() = default;
 
-    void registerNewObject(JSObject* res);
-    void unregisterObject(JSObject* obj);
+    void registerNewObject(PlainObject* res);
+    void unregisterObject(PlainObject* obj);
 
     JSObject* get(size_t i) const {
         MOZ_ASSERT(i < COUNT);
diff --git a/js/src/vm/UnboxedObject-inl.h b/js/src/vm/UnboxedObject-inl.h
deleted file mode 100644
index 93ad7bf28..000000000
--- a/js/src/vm/UnboxedObject-inl.h
+++ /dev/null
@@ -1,840 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
- * vim: set ts=8 sts=4 et sw=4 tw=99:
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef vm_UnboxedObject_inl_h
-#define vm_UnboxedObject_inl_h
-
-#include "vm/UnboxedObject.h"
-
-#include "gc/StoreBuffer-inl.h"
-#include "vm/ArrayObject-inl.h"
-#include "vm/NativeObject-inl.h"
-
-namespace js {
-
-static inline Value
-GetUnboxedValue(uint8_t* p, JSValueType type, bool maybeUninitialized)
-{
-    switch (type) {
-      case JSVAL_TYPE_BOOLEAN:
-        return BooleanValue(*p != 0);
-
-      case JSVAL_TYPE_INT32:
-        return Int32Value(*reinterpret_cast<int32_t*>(p));
-
-      case JSVAL_TYPE_DOUBLE: {
-        // During unboxed plain object creation, non-GC thing properties are
-        // left uninitialized. This is normally fine, since the properties will
-        // be filled in shortly, but if they are read before that happens we
-        // need to make sure that doubles are canonical.
-        double d = *reinterpret_cast<double*>(p);
-        if (maybeUninitialized)
-            return DoubleValue(JS::CanonicalizeNaN(d));
-        return DoubleValue(d);
-      }
-
-      case JSVAL_TYPE_STRING:
-        return StringValue(*reinterpret_cast<JSString**>(p));
-
-      case JSVAL_TYPE_OBJECT:
-        return ObjectOrNullValue(*reinterpret_cast<JSObject**>(p));
-
-      default:
-        MOZ_CRASH("Invalid type for unboxed value");
-    }
-}
-
-static inline void
-SetUnboxedValueNoTypeChange(JSObject* unboxedObject,
-                            uint8_t* p, JSValueType type, const Value& v,
-                            bool preBarrier)
-{
-    switch (type) {
-      case JSVAL_TYPE_BOOLEAN:
-        *p = v.toBoolean();
-        return;
-
-      case JSVAL_TYPE_INT32:
-        *reinterpret_cast<int32_t*>(p) = v.toInt32();
-        return;
-
-      case JSVAL_TYPE_DOUBLE:
-        *reinterpret_cast<double*>(p) = v.toNumber();
-        return;
-
-      case JSVAL_TYPE_STRING: {
-        MOZ_ASSERT(!IsInsideNursery(v.toString()));
-        JSString** np = reinterpret_cast<JSString**>(p);
-        if (preBarrier)
-            JSString::writeBarrierPre(*np);
-        *np = v.toString();
-        return;
-      }
-
-      case JSVAL_TYPE_OBJECT: {
-        JSObject** np = reinterpret_cast<JSObject**>(p);
-
-        // Manually trigger post barriers on the whole object. If we treat
-        // the pointer as a HeapPtrObject we will get confused later if the
-        // object is converted to its native representation.
-        JSObject* obj = v.toObjectOrNull();
-        if (IsInsideNursery(obj) && !IsInsideNursery(unboxedObject)) {
-            JSRuntime* rt = unboxedObject->runtimeFromMainThread();
-            rt->gc.storeBuffer.putWholeCell(unboxedObject);
-        }
-
-        if (preBarrier)
-            JSObject::writeBarrierPre(*np);
-        *np = obj;
-        return;
-      }
-
-      default:
-        MOZ_CRASH("Invalid type for unboxed value");
-    }
-}
-
-static inline bool
-SetUnboxedValue(ExclusiveContext* cx, JSObject* unboxedObject, jsid id,
-                uint8_t* p, JSValueType type, const Value& v, bool preBarrier)
-{
-    switch (type) {
-      case JSVAL_TYPE_BOOLEAN:
-        if (v.isBoolean()) {
-            *p = v.toBoolean();
-            return true;
-        }
-        return false;
-
-      case JSVAL_TYPE_INT32:
-        if (v.isInt32()) {
-            *reinterpret_cast<int32_t*>(p) = v.toInt32();
-            return true;
-        }
-        return false;
-
-      case JSVAL_TYPE_DOUBLE:
-        if (v.isNumber()) {
-            *reinterpret_cast<double*>(p) = v.toNumber();
-            return true;
-        }
-        return false;
-
-      case JSVAL_TYPE_STRING:
-        if (v.isString()) {
-            MOZ_ASSERT(!IsInsideNursery(v.toString()));
-            JSString** np = reinterpret_cast<JSString**>(p);
-            if (preBarrier)
-                JSString::writeBarrierPre(*np);
-            *np = v.toString();
-            return true;
-        }
-        return false;
-
-      case JSVAL_TYPE_OBJECT:
-        if (v.isObjectOrNull()) {
-            JSObject** np = reinterpret_cast<JSObject**>(p);
-
-            // Update property types when writing object properties. Types for
-            // other properties were captured when the unboxed layout was
-            // created.
-            AddTypePropertyId(cx, unboxedObject, id, v);
-
-            // As above, trigger post barriers on the whole object.
-            JSObject* obj = v.toObjectOrNull();
-            if (IsInsideNursery(v.toObjectOrNull()) && !IsInsideNursery(unboxedObject)) {
-                JSRuntime* rt = unboxedObject->runtimeFromMainThread();
-                rt->gc.storeBuffer.putWholeCell(unboxedObject);
-            }
-
-            if (preBarrier)
-                JSObject::writeBarrierPre(*np);
-            *np = obj;
-            return true;
-        }
-        return false;
-
-      default:
-        MOZ_CRASH("Invalid type for unboxed value");
-    }
-}
-
-/////////////////////////////////////////////////////////////////////
-// UnboxedPlainObject
-/////////////////////////////////////////////////////////////////////
-
-inline const UnboxedLayout&
-UnboxedPlainObject::layout() const
-{
-    return group()->unboxedLayout();
-}
-
-/////////////////////////////////////////////////////////////////////
-// UnboxedArrayObject
-/////////////////////////////////////////////////////////////////////
-
-inline const UnboxedLayout&
-UnboxedArrayObject::layout() const
-{
-    return group()->unboxedLayout();
-}
-
-inline void
-UnboxedArrayObject::setLength(ExclusiveContext* cx, uint32_t length)
-{
-    if (length > INT32_MAX) {
-        // Track objects with overflowing lengths in type information.
-        MarkObjectGroupFlags(cx, this, OBJECT_FLAG_LENGTH_OVERFLOW);
-    }
-
-    length_ = length;
-}
-
-inline void
-UnboxedArrayObject::setInitializedLength(uint32_t initlen)
-{
-    if (initlen < initializedLength()) {
-        switch (elementType()) {
-          case JSVAL_TYPE_STRING:
-            for (size_t i = initlen; i < initializedLength(); i++)
-                triggerPreBarrier<JSVAL_TYPE_STRING>(i);
-            break;
-          case JSVAL_TYPE_OBJECT:
-            for (size_t i = initlen; i < initializedLength(); i++)
-                triggerPreBarrier<JSVAL_TYPE_OBJECT>(i);
-            break;
-          default:
-            MOZ_ASSERT(!UnboxedTypeNeedsPreBarrier(elementType()));
-        }
-    }
-    setInitializedLengthNoBarrier(initlen);
-}
-
-template <JSValueType Type>
-inline bool
-UnboxedArrayObject::setElementSpecific(ExclusiveContext* cx, size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    MOZ_ASSERT(Type == elementType());
-    uint8_t* p = elements() + index * UnboxedTypeSize(Type);
-    return SetUnboxedValue(cx, this, JSID_VOID, p, elementType(), v, /* preBarrier = */ true);
-}
-
-template <JSValueType Type>
-inline void
-UnboxedArrayObject::setElementNoTypeChangeSpecific(size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    MOZ_ASSERT(Type == elementType());
-    uint8_t* p = elements() + index * UnboxedTypeSize(Type);
-    return SetUnboxedValueNoTypeChange(this, p, elementType(), v, /* preBarrier = */ true);
-}
-
-template <JSValueType Type>
-inline bool
-UnboxedArrayObject::initElementSpecific(ExclusiveContext* cx, size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    MOZ_ASSERT(Type == elementType());
-    uint8_t* p = elements() + index * UnboxedTypeSize(Type);
-    return SetUnboxedValue(cx, this, JSID_VOID, p, elementType(), v, /* preBarrier = */ false);
-}
-
-template <JSValueType Type>
-inline void
-UnboxedArrayObject::initElementNoTypeChangeSpecific(size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    MOZ_ASSERT(Type == elementType());
-    uint8_t* p = elements() + index * UnboxedTypeSize(Type);
-    return SetUnboxedValueNoTypeChange(this, p, elementType(), v, /* preBarrier = */ false);
-}
-
-template <JSValueType Type>
-inline Value
-UnboxedArrayObject::getElementSpecific(size_t index)
-{
-    MOZ_ASSERT(index < initializedLength());
-    MOZ_ASSERT(Type == elementType());
-    uint8_t* p = elements() + index * UnboxedTypeSize(Type);
-    return GetUnboxedValue(p, Type, /* maybeUninitialized = */ false);
-}
-
-template <JSValueType Type>
-inline void
-UnboxedArrayObject::triggerPreBarrier(size_t index)
-{
-    MOZ_ASSERT(UnboxedTypeNeedsPreBarrier(Type));
-
-    uint8_t* p = elements() + index * UnboxedTypeSize(Type);
-
-    switch (Type) {
-      case JSVAL_TYPE_STRING: {
-        JSString** np = reinterpret_cast<JSString**>(p);
-        JSString::writeBarrierPre(*np);
-        break;
-      }
-
-      case JSVAL_TYPE_OBJECT: {
-        JSObject** np = reinterpret_cast<JSObject**>(p);
-        JSObject::writeBarrierPre(*np);
-        break;
-      }
-
-      default:
-        MOZ_CRASH("Bad type");
-    }
-}
-
-/////////////////////////////////////////////////////////////////////
-// Combined methods for NativeObject and UnboxedArrayObject accesses.
-/////////////////////////////////////////////////////////////////////
-
-static inline bool
-HasAnyBoxedOrUnboxedDenseElements(JSObject* obj)
-{
-    return obj->isNative() || obj->is<UnboxedArrayObject>();
-}
-
-static inline size_t
-GetAnyBoxedOrUnboxedInitializedLength(JSObject* obj)
-{
-    if (obj->isNative())
-        return obj->as<NativeObject>().getDenseInitializedLength();
-    if (obj->is<UnboxedArrayObject>())
-        return obj->as<UnboxedArrayObject>().initializedLength();
-    return 0;
-}
-
-static inline size_t
-GetAnyBoxedOrUnboxedCapacity(JSObject* obj)
-{
-    if (obj->isNative())
-        return obj->as<NativeObject>().getDenseCapacity();
-    if (obj->is<UnboxedArrayObject>())
-        return obj->as<UnboxedArrayObject>().capacity();
-    return 0;
-}
-
-static inline Value
-GetAnyBoxedOrUnboxedDenseElement(JSObject* obj, size_t index)
-{
-    if (obj->isNative())
-        return obj->as<NativeObject>().getDenseElement(index);
-    return obj->as<UnboxedArrayObject>().getElement(index);
-}
-
-static inline size_t
-GetAnyBoxedOrUnboxedArrayLength(JSObject* obj)
-{
-    if (obj->is<ArrayObject>())
-        return obj->as<ArrayObject>().length();
-    return obj->as<UnboxedArrayObject>().length();
-}
-
-static inline void
-SetAnyBoxedOrUnboxedArrayLength(JSContext* cx, JSObject* obj, size_t length)
-{
-    if (obj->is<ArrayObject>()) {
-        MOZ_ASSERT(length >= obj->as<ArrayObject>().length());
-        obj->as<ArrayObject>().setLength(cx, length);
-    } else {
-        MOZ_ASSERT(length >= obj->as<UnboxedArrayObject>().length());
-        obj->as<UnboxedArrayObject>().setLength(cx, length);
-    }
-}
-
-static inline bool
-SetAnyBoxedOrUnboxedDenseElement(JSContext* cx, JSObject* obj, size_t index, const Value& value)
-{
-    if (obj->isNative()) {
-        obj->as<NativeObject>().setDenseElementWithType(cx, index, value);
-        return true;
-    }
-    return obj->as<UnboxedArrayObject>().setElement(cx, index, value);
-}
-
-static inline bool
-InitAnyBoxedOrUnboxedDenseElement(JSContext* cx, JSObject* obj, size_t index, const Value& value)
-{
-    if (obj->isNative()) {
-        obj->as<NativeObject>().initDenseElementWithType(cx, index, value);
-        return true;
-    }
-    return obj->as<UnboxedArrayObject>().initElement(cx, index, value);
-}
-
-/////////////////////////////////////////////////////////////////////
-// Template methods for NativeObject and UnboxedArrayObject accesses.
-/////////////////////////////////////////////////////////////////////
-
-static inline JSValueType
-GetBoxedOrUnboxedType(JSObject* obj)
-{
-    if (obj->isNative())
-        return JSVAL_TYPE_MAGIC;
-    return obj->as<UnboxedArrayObject>().elementType();
-}
-
-template <JSValueType Type>
-static inline bool
-HasBoxedOrUnboxedDenseElements(JSObject* obj)
-{
-    if (Type == JSVAL_TYPE_MAGIC)
-        return obj->isNative();
-    return obj->is<UnboxedArrayObject>() && obj->as<UnboxedArrayObject>().elementType() == Type;
-}
-
-template <JSValueType Type>
-static inline size_t
-GetBoxedOrUnboxedInitializedLength(JSObject* obj)
-{
-    if (Type == JSVAL_TYPE_MAGIC)
-        return obj->as<NativeObject>().getDenseInitializedLength();
-    return obj->as<UnboxedArrayObject>().initializedLength();
-}
-
-template <JSValueType Type>
-static inline DenseElementResult
-SetBoxedOrUnboxedInitializedLength(JSContext* cx, JSObject* obj, size_t initlen)
-{
-    size_t oldInitlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
-    if (Type == JSVAL_TYPE_MAGIC) {
-        obj->as<NativeObject>().setDenseInitializedLength(initlen);
-        if (initlen < oldInitlen)
-            obj->as<NativeObject>().shrinkElements(cx, initlen);
-    } else {
-        obj->as<UnboxedArrayObject>().setInitializedLength(initlen);
-        if (initlen < oldInitlen)
-            obj->as<UnboxedArrayObject>().shrinkElements(cx, initlen);
-    }
-    return DenseElementResult::Success;
-}
-
-template <JSValueType Type>
-static inline size_t
-GetBoxedOrUnboxedCapacity(JSObject* obj)
-{
-    if (Type == JSVAL_TYPE_MAGIC)
-        return obj->as<NativeObject>().getDenseCapacity();
-    return obj->as<UnboxedArrayObject>().capacity();
-}
-
-template <JSValueType Type>
-static inline Value
-GetBoxedOrUnboxedDenseElement(JSObject* obj, size_t index)
-{
-    if (Type == JSVAL_TYPE_MAGIC)
-        return obj->as<NativeObject>().getDenseElement(index);
-    return obj->as<UnboxedArrayObject>().getElementSpecific<Type>(index);
-}
-
-template <JSValueType Type>
-static inline void
-SetBoxedOrUnboxedDenseElementNoTypeChange(JSObject* obj, size_t index, const Value& value)
-{
-    if (Type == JSVAL_TYPE_MAGIC)
-        obj->as<NativeObject>().setDenseElement(index, value);
-    else
-        obj->as<UnboxedArrayObject>().setElementNoTypeChangeSpecific<Type>(index, value);
-}
-
-template <JSValueType Type>
-static inline bool
-SetBoxedOrUnboxedDenseElement(JSContext* cx, JSObject* obj, size_t index, const Value& value)
-{
-    if (Type == JSVAL_TYPE_MAGIC) {
-        obj->as<NativeObject>().setDenseElementWithType(cx, index, value);
-        return true;
-    }
-    return obj->as<UnboxedArrayObject>().setElementSpecific<Type>(cx, index, value);
-}
-
-template <JSValueType Type>
-static inline DenseElementResult
-EnsureBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* obj, size_t count)
-{
-    if (Type == JSVAL_TYPE_MAGIC) {
-        if (!obj->as<ArrayObject>().ensureElements(cx, count))
-            return DenseElementResult::Failure;
-    } else {
-        if (obj->as<UnboxedArrayObject>().capacity() < count) {
-            if (!obj->as<UnboxedArrayObject>().growElements(cx, count))
-                return DenseElementResult::Failure;
-        }
-    }
-    return DenseElementResult::Success;
-}
-
-template <JSValueType Type>
-static inline DenseElementResult
-SetOrExtendBoxedOrUnboxedDenseElements(ExclusiveContext* cx, JSObject* obj,
-                                       uint32_t start, const Value* vp, uint32_t count,
-                                       ShouldUpdateTypes updateTypes = ShouldUpdateTypes::Update)
-{
-    if (Type == JSVAL_TYPE_MAGIC) {
-        NativeObject* nobj = &obj->as<NativeObject>();
-
-        if (nobj->denseElementsAreFrozen())
-            return DenseElementResult::Incomplete;
-
-        if (obj->is<ArrayObject>() &&
-            !obj->as<ArrayObject>().lengthIsWritable() &&
-            start + count >= obj->as<ArrayObject>().length())
-        {
-            return DenseElementResult::Incomplete;
-        }
-
-        DenseElementResult result = nobj->ensureDenseElements(cx, start, count);
-        if (result != DenseElementResult::Success)
-            return result;
-
-        if (obj->is<ArrayObject>() && start + count >= obj->as<ArrayObject>().length())
-            obj->as<ArrayObject>().setLengthInt32(start + count);
-
-        if (updateTypes == ShouldUpdateTypes::DontUpdate && !nobj->shouldConvertDoubleElements()) {
-            nobj->copyDenseElements(start, vp, count);
-        } else {
-            for (size_t i = 0; i < count; i++)
-                nobj->setDenseElementWithType(cx, start + i, vp[i]);
-        }
-
-        return DenseElementResult::Success;
-    }
-
-    UnboxedArrayObject* nobj = &obj->as<UnboxedArrayObject>();
-
-    if (start > nobj->initializedLength())
-        return DenseElementResult::Incomplete;
-
-    if (start + count >= UnboxedArrayObject::MaximumCapacity)
-        return DenseElementResult::Incomplete;
-
-    if (start + count > nobj->capacity() && !nobj->growElements(cx, start + count))
-        return DenseElementResult::Failure;
-
-    size_t oldInitlen = nobj->initializedLength();
-
-    // Overwrite any existing elements covered by the new range. If we fail
-    // after this point due to some incompatible type being written to the
-    // object's elements, afterwards the contents will be different from when
-    // we started. The caller must retry the operation using a generic path,
-    // which will overwrite the already-modified elements as well as the ones
-    // that were left alone.
-    size_t i = 0;
-    if (updateTypes == ShouldUpdateTypes::DontUpdate) {
-        for (size_t j = start; i < count && j < oldInitlen; i++, j++)
-            nobj->setElementNoTypeChangeSpecific<Type>(j, vp[i]);
-    } else {
-        for (size_t j = start; i < count && j < oldInitlen; i++, j++) {
-            if (!nobj->setElementSpecific<Type>(cx, j, vp[i]))
-                return DenseElementResult::Incomplete;
-        }
-    }
-
-    if (i != count) {
-        obj->as<UnboxedArrayObject>().setInitializedLength(start + count);
-        if (updateTypes == ShouldUpdateTypes::DontUpdate) {
-            for (; i < count; i++)
-                nobj->initElementNoTypeChangeSpecific<Type>(start + i, vp[i]);
-        } else {
-            for (; i < count; i++) {
-                if (!nobj->initElementSpecific<Type>(cx, start + i, vp[i])) {
-                    nobj->setInitializedLengthNoBarrier(oldInitlen);
-                    return DenseElementResult::Incomplete;
-                }
-            }
-        }
-    }
-
-    if (start + count >= nobj->length())
-        nobj->setLength(cx, start + count);
-
-    return DenseElementResult::Success;
-}
-
-template <JSValueType Type>
-static inline DenseElementResult
-MoveBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* obj, uint32_t dstStart, uint32_t srcStart,
-                                uint32_t length)
-{
-    MOZ_ASSERT(HasBoxedOrUnboxedDenseElements<Type>(obj));
-
-    if (Type == JSVAL_TYPE_MAGIC) {
-        if (obj->as<NativeObject>().denseElementsAreFrozen())
-            return DenseElementResult::Incomplete;
-
-        if (!obj->as<NativeObject>().maybeCopyElementsForWrite(cx))
-            return DenseElementResult::Failure;
-        obj->as<NativeObject>().moveDenseElements(dstStart, srcStart, length);
-    } else {
-        uint8_t* data = obj->as<UnboxedArrayObject>().elements();
-        size_t elementSize = UnboxedTypeSize(Type);
-
-        if (UnboxedTypeNeedsPreBarrier(Type) &&
-            JS::shadow::Zone::asShadowZone(obj->zone())->needsIncrementalBarrier())
-        {
-            // Trigger pre barriers on any elements we are overwriting. See
-            // NativeObject::moveDenseElements. No post barrier is needed as
-            // only whole cell post barriers are used with unboxed objects.
-            for (size_t i = 0; i < length; i++)
-                obj->as<UnboxedArrayObject>().triggerPreBarrier<Type>(dstStart + i);
-        }
-
-        memmove(data + dstStart * elementSize,
-                data + srcStart * elementSize,
-                length * elementSize);
-    }
-
-    return DenseElementResult::Success;
-}
-
-template <JSValueType DstType, JSValueType SrcType>
-static inline DenseElementResult
-CopyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* dst, JSObject* src,
-                                uint32_t dstStart, uint32_t srcStart, uint32_t length)
-{
-    MOZ_ASSERT(HasBoxedOrUnboxedDenseElements<SrcType>(src));
-    MOZ_ASSERT(HasBoxedOrUnboxedDenseElements<DstType>(dst));
-    MOZ_ASSERT(GetBoxedOrUnboxedInitializedLength<DstType>(dst) == dstStart);
-    MOZ_ASSERT(GetBoxedOrUnboxedInitializedLength<SrcType>(src) >= srcStart + length);
-    MOZ_ASSERT(GetBoxedOrUnboxedCapacity<DstType>(dst) >= dstStart + length);
-
-    SetBoxedOrUnboxedInitializedLength<DstType>(cx, dst, dstStart + length);
-
-    if (DstType == JSVAL_TYPE_MAGIC) {
-        if (SrcType == JSVAL_TYPE_MAGIC) {
-            const Value* vp = src->as<NativeObject>().getDenseElements() + srcStart;
-            dst->as<NativeObject>().initDenseElements(dstStart, vp, length);
-        } else {
-            for (size_t i = 0; i < length; i++) {
-                Value v = GetBoxedOrUnboxedDenseElement<SrcType>(src, srcStart + i);
-                dst->as<NativeObject>().initDenseElement(dstStart + i, v);
-            }
-        }
-    } else if (DstType == SrcType) {
-        uint8_t* dstData = dst->as<UnboxedArrayObject>().elements();
-        uint8_t* srcData = src->as<UnboxedArrayObject>().elements();
-        size_t elementSize = UnboxedTypeSize(DstType);
-
-        memcpy(dstData + dstStart * elementSize,
-               srcData + srcStart * elementSize,
-               length * elementSize);
-
-        // Add a store buffer entry if we might have copied a nursery pointer to dst.
-        if (UnboxedTypeNeedsPostBarrier(DstType) && !IsInsideNursery(dst))
-            dst->runtimeFromMainThread()->gc.storeBuffer.putWholeCell(dst);
-    } else if (DstType == JSVAL_TYPE_DOUBLE && SrcType == JSVAL_TYPE_INT32) {
-        uint8_t* dstData = dst->as<UnboxedArrayObject>().elements();
-        uint8_t* srcData = src->as<UnboxedArrayObject>().elements();
-
-        for (size_t i = 0; i < length; i++) {
-            int32_t v = *reinterpret_cast<int32_t*>(srcData + (srcStart + i) * sizeof(int32_t));
-            *reinterpret_cast<double*>(dstData + (dstStart + i) * sizeof(double)) = v;
-        }
-    } else {
-        for (size_t i = 0; i < length; i++) {
-            Value v = GetBoxedOrUnboxedDenseElement<SrcType>(src, srcStart + i);
-            dst->as<UnboxedArrayObject>().initElementNoTypeChangeSpecific<DstType>(dstStart + i, v);
-        }
-    }
-
-    return DenseElementResult::Success;
-}
-
-/////////////////////////////////////////////////////////////////////
-// Dispatch to specialized methods based on the type of an object.
-/////////////////////////////////////////////////////////////////////
-
-// Goop to fix MSVC. See DispatchTraceKindTyped in TraceKind.h.
-// The clang-cl front end defines _MSC_VER, but still requires the explicit
-// template declaration, so we must test for __clang__ here as well.
-#if defined(_MSC_VER) && !defined(__clang__)
-# define DEPENDENT_TEMPLATE_HINT
-#else
-# define DEPENDENT_TEMPLATE_HINT template
-#endif
-
-// Function to dispatch a method specialized to whatever boxed or unboxed dense
-// elements which an input object has.
-template <typename F>
-DenseElementResult
-CallBoxedOrUnboxedSpecialization(F f, JSObject* obj)
-{
-    if (!HasAnyBoxedOrUnboxedDenseElements(obj))
-        return DenseElementResult::Incomplete;
-    switch (GetBoxedOrUnboxedType(obj)) {
-      case JSVAL_TYPE_MAGIC:
-        return f. DEPENDENT_TEMPLATE_HINT operator()<JSVAL_TYPE_MAGIC>();
-      case JSVAL_TYPE_BOOLEAN:
-        return f. DEPENDENT_TEMPLATE_HINT operator()<JSVAL_TYPE_BOOLEAN>();
-      case JSVAL_TYPE_INT32:
-        return f. DEPENDENT_TEMPLATE_HINT operator()<JSVAL_TYPE_INT32>();
-      case JSVAL_TYPE_DOUBLE:
-        return f. DEPENDENT_TEMPLATE_HINT operator()<JSVAL_TYPE_DOUBLE>();
-      case JSVAL_TYPE_STRING:
-        return f. DEPENDENT_TEMPLATE_HINT operator()<JSVAL_TYPE_STRING>();
-      case JSVAL_TYPE_OBJECT:
-        return f. DEPENDENT_TEMPLATE_HINT operator()<JSVAL_TYPE_OBJECT>();
-      default:
-        MOZ_CRASH();
-    }
-}
-
-// As above, except the specialization can reflect the unboxed type of two objects.
-template <typename F>
-DenseElementResult
-CallBoxedOrUnboxedSpecialization(F f, JSObject* obj1, JSObject* obj2)
-{
-    if (!HasAnyBoxedOrUnboxedDenseElements(obj1) || !HasAnyBoxedOrUnboxedDenseElements(obj2))
-        return DenseElementResult::Incomplete;
-
-#define SPECIALIZE_OBJ2(TYPE)                                                     \
-    switch (GetBoxedOrUnboxedType(obj2)) {                                        \
-      case JSVAL_TYPE_MAGIC:                                                      \
-        return f. DEPENDENT_TEMPLATE_HINT operator()<TYPE, JSVAL_TYPE_MAGIC>();   \
-      case JSVAL_TYPE_BOOLEAN:                                                    \
-        return f. DEPENDENT_TEMPLATE_HINT operator()<TYPE, JSVAL_TYPE_BOOLEAN>(); \
-      case JSVAL_TYPE_INT32:                                                      \
-        return f. DEPENDENT_TEMPLATE_HINT operator()<TYPE, JSVAL_TYPE_INT32>();   \
-      case JSVAL_TYPE_DOUBLE:                                                     \
-        return f. DEPENDENT_TEMPLATE_HINT operator()<TYPE, JSVAL_TYPE_DOUBLE>();  \
-      case JSVAL_TYPE_STRING:                                                     \
-        return f. DEPENDENT_TEMPLATE_HINT operator()<TYPE, JSVAL_TYPE_STRING>();  \
-      case JSVAL_TYPE_OBJECT:                                                     \
-        return f. DEPENDENT_TEMPLATE_HINT operator()<TYPE, JSVAL_TYPE_OBJECT>();  \
-      default:                                                                    \
-        MOZ_CRASH();                                                              \
-    }
-
-    switch (GetBoxedOrUnboxedType(obj1)) {
-      case JSVAL_TYPE_MAGIC:
-        SPECIALIZE_OBJ2(JSVAL_TYPE_MAGIC)
-      case JSVAL_TYPE_BOOLEAN:
-        SPECIALIZE_OBJ2(JSVAL_TYPE_BOOLEAN)
-      case JSVAL_TYPE_INT32:
-        SPECIALIZE_OBJ2(JSVAL_TYPE_INT32)
-      case JSVAL_TYPE_DOUBLE:
-        SPECIALIZE_OBJ2(JSVAL_TYPE_DOUBLE)
-      case JSVAL_TYPE_STRING:
-        SPECIALIZE_OBJ2(JSVAL_TYPE_STRING)
-      case JSVAL_TYPE_OBJECT:
-        SPECIALIZE_OBJ2(JSVAL_TYPE_OBJECT)
-      default:
-        MOZ_CRASH();
-    }
-
-#undef SPECIALIZE_OBJ2
-}
-
-#undef DEPENDENT_TEMPLATE_HINT
-
-#define DefineBoxedOrUnboxedFunctor1(Signature, A)                      \
-struct Signature ## Functor {                                           \
-    A a;                                                                \
-    explicit Signature ## Functor(A a)                                  \
-      : a(a)                                                            \
-    {}                                                                  \
-    template <JSValueType Type>                                         \
-    DenseElementResult operator()() {                                   \
-        return Signature<Type>(a);                                      \
-    }                                                                   \
-}
-
-#define DefineBoxedOrUnboxedFunctor3(Signature, A, B, C)                \
-struct Signature ## Functor {                                           \
-    A a; B b; C c;                                                      \
-    Signature ## Functor(A a, B b, C c)                                 \
-      : a(a), b(b), c(c)                                                \
-    {}                                                                  \
-    template <JSValueType Type>                                         \
-    DenseElementResult operator()() {                                   \
-        return Signature<Type>(a, b, c);                                \
-    }                                                                   \
-}
-
-#define DefineBoxedOrUnboxedFunctor4(Signature, A, B, C, D)             \
-struct Signature ## Functor {                                           \
-    A a; B b; C c; D d;                                                 \
-    Signature ## Functor(A a, B b, C c, D d)                            \
-      : a(a), b(b), c(c), d(d)                                          \
-    {}                                                                  \
-    template <JSValueType Type>                                         \
-    DenseElementResult operator()() {                                   \
-        return Signature<Type>(a, b, c, d);                             \
-    }                                                                   \
-}
-
-#define DefineBoxedOrUnboxedFunctorPair4(Signature, A, B, C, D)         \
-struct Signature ## Functor {                                           \
-    A a; B b; C c; D d;                                                 \
-    Signature ## Functor(A a, B b, C c, D d)                            \
-      : a(a), b(b), c(c), d(d)                                          \
-    {}                                                                  \
-    template <JSValueType TypeOne, JSValueType TypeTwo>                 \
-    DenseElementResult operator()() {                                   \
-        return Signature<TypeOne, TypeTwo>(a, b, c, d);                 \
-    }                                                                   \
-}
-
-#define DefineBoxedOrUnboxedFunctor5(Signature, A, B, C, D, E)          \
-struct Signature ## Functor {                                           \
-    A a; B b; C c; D d; E e;                                            \
-    Signature ## Functor(A a, B b, C c, D d, E e)                       \
-      : a(a), b(b), c(c), d(d), e(e)                                    \
-    {}                                                                  \
-    template <JSValueType Type>                                         \
-    DenseElementResult operator()() {                                   \
-        return Signature<Type>(a, b, c, d, e);                          \
-    }                                                                   \
-}
-
-#define DefineBoxedOrUnboxedFunctor6(Signature, A, B, C, D, E, F)       \
-struct Signature ## Functor {                                           \
-    A a; B b; C c; D d; E e; F f;                                       \
-    Signature ## Functor(A a, B b, C c, D d, E e, F f)                  \
-      : a(a), b(b), c(c), d(d), e(e), f(f)                              \
-    {}                                                                  \
-    template <JSValueType Type>                                         \
-    DenseElementResult operator()() {                                   \
-        return Signature<Type>(a, b, c, d, e, f);                       \
-    }                                                                   \
-}
-
-#define DefineBoxedOrUnboxedFunctorPair6(Signature, A, B, C, D, E, F)   \
-struct Signature ## Functor {                                           \
-    A a; B b; C c; D d; E e; F f;                                       \
-    Signature ## Functor(A a, B b, C c, D d, E e, F f)                  \
-      : a(a), b(b), c(c), d(d), e(e), f(f)                              \
-    {}                                                                  \
-    template <JSValueType TypeOne, JSValueType TypeTwo>                 \
-    DenseElementResult operator()() {                                   \
-        return Signature<TypeOne, TypeTwo>(a, b, c, d, e, f);           \
-    }                                                                   \
-}
-
-DenseElementResult
-SetOrExtendAnyBoxedOrUnboxedDenseElements(ExclusiveContext* cx, JSObject* obj,
-                                          uint32_t start, const Value* vp, uint32_t count,
-                                          ShouldUpdateTypes updateTypes = ShouldUpdateTypes::Update);
-
-DenseElementResult
-MoveAnyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* obj,
-                                   uint32_t dstStart, uint32_t srcStart, uint32_t length);
-
-DenseElementResult
-CopyAnyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* dst, JSObject* src,
-                                   uint32_t dstStart, uint32_t srcStart, uint32_t length);
-
-void
-SetAnyBoxedOrUnboxedInitializedLength(JSContext* cx, JSObject* obj, size_t initlen);
-
-DenseElementResult
-EnsureAnyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* obj, size_t count);
-
-} // namespace js
-
-#endif // vm_UnboxedObject_inl_h
diff --git a/js/src/vm/UnboxedObject.cpp b/js/src/vm/UnboxedObject.cpp
deleted file mode 100644
index 3018ace67..000000000
--- a/js/src/vm/UnboxedObject.cpp
+++ /dev/null
@@ -1,2152 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
- * vim: set ts=8 sts=4 et sw=4 tw=99:
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "vm/UnboxedObject-inl.h"
-
-#include "jit/BaselineIC.h"
-#include "jit/ExecutableAllocator.h"
-#include "jit/JitCommon.h"
-#include "jit/Linker.h"
-
-#include "jsobjinlines.h"
-
-#include "gc/Nursery-inl.h"
-#include "jit/MacroAssembler-inl.h"
-#include "vm/Shape-inl.h"
-
-using mozilla::ArrayLength;
-using mozilla::DebugOnly;
-using mozilla::PodCopy;
-
-using namespace js;
-
-/////////////////////////////////////////////////////////////////////
-// UnboxedLayout
-/////////////////////////////////////////////////////////////////////
-
-void
-UnboxedLayout::trace(JSTracer* trc)
-{
-    for (size_t i = 0; i < properties_.length(); i++)
-        TraceManuallyBarrieredEdge(trc, &properties_[i].name, "unboxed_layout_name");
-
-    if (newScript())
-        newScript()->trace(trc);
-
-    TraceNullableEdge(trc, &nativeGroup_, "unboxed_layout_nativeGroup");
-    TraceNullableEdge(trc, &nativeShape_, "unboxed_layout_nativeShape");
-    TraceNullableEdge(trc, &allocationScript_, "unboxed_layout_allocationScript");
-    TraceNullableEdge(trc, &replacementGroup_, "unboxed_layout_replacementGroup");
-    TraceNullableEdge(trc, &constructorCode_, "unboxed_layout_constructorCode");
-}
-
-size_t
-UnboxedLayout::sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf)
-{
-    return mallocSizeOf(this)
-         + properties_.sizeOfExcludingThis(mallocSizeOf)
-         + (newScript() ? newScript()->sizeOfIncludingThis(mallocSizeOf) : 0)
-         + mallocSizeOf(traceList());
-}
-
-void
-UnboxedLayout::setNewScript(TypeNewScript* newScript, bool writeBarrier /* = true */)
-{
-    if (newScript_ && writeBarrier)
-        TypeNewScript::writeBarrierPre(newScript_);
-    newScript_ = newScript;
-}
-
-// Constructor code returns a 0x1 value to indicate the constructor code should
-// be cleared.
-static const uintptr_t CLEAR_CONSTRUCTOR_CODE_TOKEN = 0x1;
-
-/* static */ bool
-UnboxedLayout::makeConstructorCode(JSContext* cx, HandleObjectGroup group)
-{
-    gc::AutoSuppressGC suppress(cx);
-
-    using namespace jit;
-
-    if (!cx->compartment()->ensureJitCompartmentExists(cx))
-        return false;
-
-    UnboxedLayout& layout = group->unboxedLayout();
-    MOZ_ASSERT(!layout.constructorCode());
-
-    UnboxedPlainObject* templateObject = UnboxedPlainObject::create(cx, group, TenuredObject);
-    if (!templateObject)
-        return false;
-
-    JitContext jitContext(cx, nullptr);
-
-    MacroAssembler masm;
-
-    Register propertiesReg, newKindReg;
-#ifdef JS_CODEGEN_X86
-    propertiesReg = eax;
-    newKindReg = ecx;
-    masm.loadPtr(Address(masm.getStackPointer(), sizeof(void*)), propertiesReg);
-    masm.loadPtr(Address(masm.getStackPointer(), 2 * sizeof(void*)), newKindReg);
-#else
-    propertiesReg = IntArgReg0;
-    newKindReg = IntArgReg1;
-#endif
-
-#ifdef JS_CODEGEN_ARM64
-    // ARM64 communicates stack address via sp, but uses a pseudo-sp for addressing.
-    masm.initStackPtr();
-#endif
-
-    MOZ_ASSERT(propertiesReg.volatile_());
-    MOZ_ASSERT(newKindReg.volatile_());
-
-    AllocatableGeneralRegisterSet regs(GeneralRegisterSet::All());
-    regs.take(propertiesReg);
-    regs.take(newKindReg);
-    Register object = regs.takeAny(), scratch1 = regs.takeAny(), scratch2 = regs.takeAny();
-
-    LiveGeneralRegisterSet savedNonVolatileRegisters = SavedNonVolatileRegisters(regs);
-    masm.PushRegsInMask(savedNonVolatileRegisters);
-
-    // The scratch double register might be used by MacroAssembler methods.
-    if (ScratchDoubleReg.volatile_())
-        masm.push(ScratchDoubleReg);
-
-    Label failure, tenuredObject, allocated;
-    masm.branch32(Assembler::NotEqual, newKindReg, Imm32(GenericObject), &tenuredObject);
-    masm.branchTest32(Assembler::NonZero, AbsoluteAddress(group->addressOfFlags()),
-                      Imm32(OBJECT_FLAG_PRE_TENURE), &tenuredObject);
-
-    // Allocate an object in the nursery
-    masm.createGCObject(object, scratch1, templateObject, gc::DefaultHeap, &failure,
-                        /* initFixedSlots = */ false);
-
-    masm.jump(&allocated);
-    masm.bind(&tenuredObject);
-
-    // Allocate an object in the tenured heap.
-    masm.createGCObject(object, scratch1, templateObject, gc::TenuredHeap, &failure,
-                        /* initFixedSlots = */ false);
-
-    // If any of the properties being stored are in the nursery, add a store
-    // buffer entry for the new object.
-    Label postBarrier;
-    for (size_t i = 0; i < layout.properties().length(); i++) {
-        const UnboxedLayout::Property& property = layout.properties()[i];
-        if (property.type == JSVAL_TYPE_OBJECT) {
-            Address valueAddress(propertiesReg, i * sizeof(IdValuePair) + offsetof(IdValuePair, value));
-            Label notObject;
-            masm.branchTestObject(Assembler::NotEqual, valueAddress, &notObject);
-            Register valueObject = masm.extractObject(valueAddress, scratch1);
-            masm.branchPtrInNurseryChunk(Assembler::Equal, valueObject, scratch2, &postBarrier);
-            masm.bind(&notObject);
-        }
-    }
-
-    masm.jump(&allocated);
-    masm.bind(&postBarrier);
-
-    LiveGeneralRegisterSet liveVolatileRegisters;
-    liveVolatileRegisters.add(propertiesReg);
-    if (object.volatile_())
-        liveVolatileRegisters.add(object);
-    masm.PushRegsInMask(liveVolatileRegisters);
-
-    masm.mov(ImmPtr(cx->runtime()), scratch1);
-    masm.setupUnalignedABICall(scratch2);
-    masm.passABIArg(scratch1);
-    masm.passABIArg(object);
-    masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, PostWriteBarrier));
-
-    masm.PopRegsInMask(liveVolatileRegisters);
-
-    masm.bind(&allocated);
-
-    ValueOperand valueOperand;
-#ifdef JS_NUNBOX32
-    valueOperand = ValueOperand(scratch1, scratch2);
-#else
-    valueOperand = ValueOperand(scratch1);
-#endif
-
-    Label failureStoreOther, failureStoreObject;
-
-    for (size_t i = 0; i < layout.properties().length(); i++) {
-        const UnboxedLayout::Property& property = layout.properties()[i];
-        Address valueAddress(propertiesReg, i * sizeof(IdValuePair) + offsetof(IdValuePair, value));
-        Address targetAddress(object, UnboxedPlainObject::offsetOfData() + property.offset);
-
-        masm.loadValue(valueAddress, valueOperand);
-
-        if (property.type == JSVAL_TYPE_OBJECT) {
-            HeapTypeSet* types = group->maybeGetProperty(IdToTypeId(NameToId(property.name)));
-
-            Label notObject;
-            masm.branchTestObject(Assembler::NotEqual, valueOperand,
-                                  types->mightBeMIRType(MIRType::Null) ? &notObject : &failureStoreObject);
-
-            Register payloadReg = masm.extractObject(valueOperand, scratch1);
-
-            if (!types->hasType(TypeSet::AnyObjectType())) {
-                Register scratch = (payloadReg == scratch1) ? scratch2 : scratch1;
-                masm.guardObjectType(payloadReg, types, scratch, &failureStoreObject);
-            }
-
-            masm.storeUnboxedProperty(targetAddress, JSVAL_TYPE_OBJECT,
-                                      TypedOrValueRegister(MIRType::Object,
-                                                           AnyRegister(payloadReg)), nullptr);
-
-            if (notObject.used()) {
-                Label done;
-                masm.jump(&done);
-                masm.bind(&notObject);
-                masm.branchTestNull(Assembler::NotEqual, valueOperand, &failureStoreOther);
-                masm.storeUnboxedProperty(targetAddress, JSVAL_TYPE_OBJECT, NullValue(), nullptr);
-                masm.bind(&done);
-            }
-        } else {
-            masm.storeUnboxedProperty(targetAddress, property.type,
-                                      ConstantOrRegister(valueOperand), &failureStoreOther);
-        }
-    }
-
-    Label done;
-    masm.bind(&done);
-
-    if (object != ReturnReg)
-        masm.movePtr(object, ReturnReg);
-
-    // Restore non-volatile registers which were saved on entry.
-    if (ScratchDoubleReg.volatile_())
-        masm.pop(ScratchDoubleReg);
-    masm.PopRegsInMask(savedNonVolatileRegisters);
-
-    masm.abiret();
-
-    masm.bind(&failureStoreOther);
-
-    // There was a failure while storing a value which cannot be stored at all
-    // in the unboxed object. Initialize the object so it is safe for GC and
-    // return null.
-    masm.initUnboxedObjectContents(object, templateObject);
-
-    masm.bind(&failure);
-
-    masm.movePtr(ImmWord(0), object);
-    masm.jump(&done);
-
-    masm.bind(&failureStoreObject);
-
-    // There was a failure while storing a value to an object slot of the
-    // unboxed object. If the value is storable, the failure occurred due to
-    // incomplete type information in the object, so return a token to trigger
-    // regeneration of the jitcode after a new object is created in the VM.
-    {
-        Label isObject;
-        masm.branchTestObject(Assembler::Equal, valueOperand, &isObject);
-        masm.branchTestNull(Assembler::NotEqual, valueOperand, &failureStoreOther);
-        masm.bind(&isObject);
-    }
-
-    // Initialize the object so it is safe for GC.
-    masm.initUnboxedObjectContents(object, templateObject);
-
-    masm.movePtr(ImmWord(CLEAR_CONSTRUCTOR_CODE_TOKEN), object);
-    masm.jump(&done);
-
-    Linker linker(masm);
-    AutoFlushICache afc("UnboxedObject");
-    JitCode* code = linker.newCode<NoGC>(cx, OTHER_CODE);
-    if (!code)
-        return false;
-
-    layout.setConstructorCode(code);
-    return true;
-}
-
-void
-UnboxedLayout::detachFromCompartment()
-{
-    if (isInList())
-        remove();
-}
-
-/////////////////////////////////////////////////////////////////////
-// UnboxedPlainObject
-/////////////////////////////////////////////////////////////////////
-
-bool
-UnboxedPlainObject::setValue(ExclusiveContext* cx, const UnboxedLayout::Property& property,
-                             const Value& v)
-{
-    uint8_t* p = &data_[property.offset];
-    return SetUnboxedValue(cx, this, NameToId(property.name), p, property.type, v,
-                           /* preBarrier = */ true);
-}
-
-Value
-UnboxedPlainObject::getValue(const UnboxedLayout::Property& property,
-                             bool maybeUninitialized /* = false */)
-{
-    uint8_t* p = &data_[property.offset];
-    return GetUnboxedValue(p, property.type, maybeUninitialized);
-}
-
-void
-UnboxedPlainObject::trace(JSTracer* trc, JSObject* obj)
-{
-    if (obj->as<UnboxedPlainObject>().expando_) {
-        TraceManuallyBarrieredEdge(trc,
-            reinterpret_cast<NativeObject**>(&obj->as<UnboxedPlainObject>().expando_),
-            "unboxed_expando");
-    }
-
-    const UnboxedLayout& layout = obj->as<UnboxedPlainObject>().layoutDontCheckGeneration();
-    const int32_t* list = layout.traceList();
-    if (!list)
-        return;
-
-    uint8_t* data = obj->as<UnboxedPlainObject>().data();
-    while (*list != -1) {
-        GCPtrString* heap = reinterpret_cast<GCPtrString*>(data + *list);
-        TraceEdge(trc, heap, "unboxed_string");
-        list++;
-    }
-    list++;
-    while (*list != -1) {
-        GCPtrObject* heap = reinterpret_cast<GCPtrObject*>(data + *list);
-        TraceNullableEdge(trc, heap, "unboxed_object");
-        list++;
-    }
-
-    // Unboxed objects don't have Values to trace.
-    MOZ_ASSERT(*(list + 1) == -1);
-}
-
-/* static */ UnboxedExpandoObject*
-UnboxedPlainObject::ensureExpando(JSContext* cx, Handle<UnboxedPlainObject*> obj)
-{
-    if (obj->expando_)
-        return obj->expando_;
-
-    UnboxedExpandoObject* expando =
-        NewObjectWithGivenProto<UnboxedExpandoObject>(cx, nullptr, gc::AllocKind::OBJECT4);
-    if (!expando)
-        return nullptr;
-
-    // Don't track property types for expando objects. This allows Baseline
-    // and Ion AddSlot ICs to guard on the unboxed group without guarding on
-    // the expando group.
-    MarkObjectGroupUnknownProperties(cx, expando->group());
-
-    // If the expando is tenured then the original object must also be tenured.
-    // Otherwise barriers triggered on the original object for writes to the
-    // expando (as can happen in the JIT) won't see the tenured->nursery edge.
-    // See WholeCellEdges::mark.
-    MOZ_ASSERT_IF(!IsInsideNursery(expando), !IsInsideNursery(obj));
-
-    // As with setValue(), we need to manually trigger post barriers on the
-    // whole object. If we treat the field as a GCPtrObject and later
-    // convert the object to its native representation, we will end up with a
-    // corrupted store buffer entry.
-    if (IsInsideNursery(expando) && !IsInsideNursery(obj))
-        cx->runtime()->gc.storeBuffer.putWholeCell(obj);
-
-    obj->expando_ = expando;
-    return expando;
-}
-
-bool
-UnboxedPlainObject::containsUnboxedOrExpandoProperty(ExclusiveContext* cx, jsid id) const
-{
-    if (layout().lookup(id))
-        return true;
-
-    if (maybeExpando() && maybeExpando()->containsShapeOrElement(cx, id))
-        return true;
-
-    return false;
-}
-
-static bool
-PropagatePropertyTypes(JSContext* cx, jsid id, ObjectGroup* oldGroup, ObjectGroup* newGroup)
-{
-    HeapTypeSet* typeProperty = oldGroup->maybeGetProperty(id);
-    TypeSet::TypeList types;
-    if (!typeProperty->enumerateTypes(&types)) {
-        ReportOutOfMemory(cx);
-        return false;
-    }
-    for (size_t j = 0; j < types.length(); j++)
-        AddTypePropertyId(cx, newGroup, nullptr, id, types[j]);
-    return true;
-}
-
-static PlainObject*
-MakeReplacementTemplateObject(JSContext* cx, HandleObjectGroup group, const UnboxedLayout &layout)
-{
-    PlainObject* obj = NewObjectWithGroup<PlainObject>(cx, group, layout.getAllocKind(),
-                                                       TenuredObject);
-    if (!obj)
-        return nullptr;
-
-    for (size_t i = 0; i < layout.properties().length(); i++) {
-        const UnboxedLayout::Property& property = layout.properties()[i];
-        if (!obj->addDataProperty(cx, NameToId(property.name), i, JSPROP_ENUMERATE))
-            return nullptr;
-        MOZ_ASSERT(obj->slotSpan() == i + 1);
-        MOZ_ASSERT(!obj->inDictionaryMode());
-    }
-
-    return obj;
-}
-
-/* static */ bool
-UnboxedLayout::makeNativeGroup(JSContext* cx, ObjectGroup* group)
-{
-    AutoEnterAnalysis enter(cx);
-
-    UnboxedLayout& layout = group->unboxedLayout();
-    Rooted<TaggedProto> proto(cx, group->proto());
-
-    MOZ_ASSERT(!layout.nativeGroup());
-
-    RootedObjectGroup replacementGroup(cx);
-
-    const Class* clasp = layout.isArray() ? &ArrayObject::class_ : &PlainObject::class_;
-
-    // Immediately clear any new script on the group. This is done by replacing
-    // the existing new script with one for a replacement default new group.
-    // This is done so that the size of the replacment group's objects is the
-    // same as that for the unboxed group, so that we do not see polymorphic
-    // slot accesses later on for sites that see converted objects from this
-    // group and objects that were allocated using the replacement new group.
-    if (layout.newScript()) {
-        MOZ_ASSERT(!layout.isArray());
-
-        replacementGroup = ObjectGroupCompartment::makeGroup(cx, &PlainObject::class_, proto);
-        if (!replacementGroup)
-            return false;
-
-        PlainObject* templateObject = MakeReplacementTemplateObject(cx, replacementGroup, layout);
-        if (!templateObject)
-            return false;
-
-        TypeNewScript* replacementNewScript =
-            TypeNewScript::makeNativeVersion(cx, layout.newScript(), templateObject);
-        if (!replacementNewScript)
-            return false;
-
-        replacementGroup->setNewScript(replacementNewScript);
-        gc::TraceTypeNewScript(replacementGroup);
-
-        group->clearNewScript(cx, replacementGroup);
-    }
-
-    // Similarly, if this group is keyed to an allocation site, replace its
-    // entry with a new group that has no unboxed layout.
-    if (layout.allocationScript()) {
-        RootedScript script(cx, layout.allocationScript());
-        jsbytecode* pc = layout.allocationPc();
-
-        replacementGroup = ObjectGroupCompartment::makeGroup(cx, clasp, proto);
-        if (!replacementGroup)
-            return false;
-
-        PlainObject* templateObject = &script->getObject(pc)->as<PlainObject>();
-        replacementGroup->addDefiniteProperties(cx, templateObject->lastProperty());
-
-        JSProtoKey key = layout.isArray() ? JSProto_Array : JSProto_Object;
-        cx->compartment()->objectGroups.replaceAllocationSiteGroup(script, pc, key,
-                                                                   replacementGroup);
-
-        // Clear any baseline information at this opcode which might use the old group.
-        if (script->hasBaselineScript()) {
-            jit::ICEntry& entry = script->baselineScript()->icEntryFromPCOffset(script->pcToOffset(pc));
-            jit::ICFallbackStub* fallback = entry.fallbackStub();
-            for (jit::ICStubIterator iter = fallback->beginChain(); !iter.atEnd(); iter++)
-                iter.unlink(cx);
-            if (fallback->isNewObject_Fallback())
-                fallback->toNewObject_Fallback()->setTemplateObject(nullptr);
-            else if (fallback->isNewArray_Fallback())
-                fallback->toNewArray_Fallback()->setTemplateGroup(replacementGroup);
-        }
-    }
-
-    size_t nfixed = layout.isArray() ? 0 : gc::GetGCKindSlots(layout.getAllocKind());
-
-    if (layout.isArray()) {
-        // The length shape to use for arrays is cached via a modified initial
-        // shape for array objects. Create an array now to make sure this entry
-        // is instantiated.
-        if (!NewDenseEmptyArray(cx))
-            return false;
-    }
-
-    RootedShape shape(cx, EmptyShape::getInitialShape(cx, clasp, proto, nfixed, 0));
-    if (!shape)
-        return false;
-
-    MOZ_ASSERT_IF(layout.isArray(), !shape->isEmptyShape() && shape->slotSpan() == 0);
-
-    // Add shapes for each property, if this is for a plain object.
-    for (size_t i = 0; i < layout.properties().length(); i++) {
-        const UnboxedLayout::Property& property = layout.properties()[i];
-
-        Rooted<StackShape> child(cx, StackShape(shape->base()->unowned(), NameToId(property.name),
-                                                i, JSPROP_ENUMERATE, 0));
-        shape = cx->zone()->propertyTree.getChild(cx, shape, child);
-        if (!shape)
-            return false;
-    }
-
-    ObjectGroup* nativeGroup =
-        ObjectGroupCompartment::makeGroup(cx, clasp, proto,
-                                          group->flags() & OBJECT_FLAG_DYNAMIC_MASK);
-    if (!nativeGroup)
-        return false;
-
-    // No sense propagating if we don't know what we started with.
-    if (!group->unknownProperties()) {
-        // Propagate all property types from the old group to the new group.
-        if (layout.isArray()) {
-            if (!PropagatePropertyTypes(cx, JSID_VOID, group, nativeGroup))
-                return false;
-        } else {
-            for (size_t i = 0; i < layout.properties().length(); i++) {
-                const UnboxedLayout::Property& property = layout.properties()[i];
-                jsid id = NameToId(property.name);
-                if (!PropagatePropertyTypes(cx, id, group, nativeGroup))
-                    return false;
-
-                // If we are OOM we may not be able to propagate properties.
-                if (nativeGroup->unknownProperties())
-                    break;
-
-                HeapTypeSet* nativeProperty = nativeGroup->maybeGetProperty(id);
-                if (nativeProperty && nativeProperty->canSetDefinite(i))
-                    nativeProperty->setDefinite(i);
-            }
-        }
-    } else {
-        // If we skip, though, the new group had better agree.
-        MOZ_ASSERT(nativeGroup->unknownProperties());
-    }
-
-    layout.nativeGroup_ = nativeGroup;
-    layout.nativeShape_ = shape;
-    layout.replacementGroup_ = replacementGroup;
-
-    nativeGroup->setOriginalUnboxedGroup(group);
-
-    group->markStateChange(cx);
-
-    return true;
-}
-
-/* static */ bool
-UnboxedPlainObject::convertToNative(JSContext* cx, JSObject* obj)
-{
-    const UnboxedLayout& layout = obj->as<UnboxedPlainObject>().layout();
-    UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando();
-
-    if (!layout.nativeGroup()) {
-        if (!UnboxedLayout::makeNativeGroup(cx, obj->group()))
-            return false;
-
-        // makeNativeGroup can reentrantly invoke this method.
-        if (obj->is<PlainObject>())
-            return true;
-    }
-
-    AutoValueVector values(cx);
-    for (size_t i = 0; i < layout.properties().length(); i++) {
-        // We might be reading properties off the object which have not been
-        // initialized yet. Make sure any double values we read here are
-        // canonicalized.
-        if (!values.append(obj->as<UnboxedPlainObject>().getValue(layout.properties()[i], true)))
-            return false;
-    }
-
-    // We are eliminating the expando edge with the conversion, so trigger a
-    // pre barrier.
-    JSObject::writeBarrierPre(expando);
-
-    // Additionally trigger a post barrier on the expando itself. Whole cell
-    // store buffer entries can be added on the original unboxed object for
-    // writes to the expando (see WholeCellEdges::trace), so after conversion
-    // we need to make sure the expando itself will still be traced.
-    if (expando && !IsInsideNursery(expando))
-        cx->runtime()->gc.storeBuffer.putWholeCell(expando);
-
-    obj->setGroup(layout.nativeGroup());
-    obj->as<PlainObject>().setLastPropertyMakeNative(cx, layout.nativeShape());
-
-    for (size_t i = 0; i < values.length(); i++)
-        obj->as<PlainObject>().initSlotUnchecked(i, values[i]);
-
-    if (expando) {
-        // Add properties from the expando object to the object, in order.
-        // Suppress GC here, so that callers don't need to worry about this
-        // method collecting. The stuff below can only fail due to OOM, in
-        // which case the object will not have been completely filled back in.
-        gc::AutoSuppressGC suppress(cx);
-
-        Vector<jsid> ids(cx);
-        for (Shape::Range<NoGC> r(expando->lastProperty()); !r.empty(); r.popFront()) {
-            if (!ids.append(r.front().propid()))
-                return false;
-        }
-        for (size_t i = 0; i < expando->getDenseInitializedLength(); i++) {
-            if (!expando->getDenseElement(i).isMagic(JS_ELEMENTS_HOLE)) {
-                if (!ids.append(INT_TO_JSID(i)))
-                    return false;
-            }
-        }
-        ::Reverse(ids.begin(), ids.end());
-
-        RootedPlainObject nobj(cx, &obj->as<PlainObject>());
-        Rooted<UnboxedExpandoObject*> nexpando(cx, expando);
-        RootedId id(cx);
-        Rooted<PropertyDescriptor> desc(cx);
-        for (size_t i = 0; i < ids.length(); i++) {
-            id = ids[i];
-            if (!GetOwnPropertyDescriptor(cx, nexpando, id, &desc))
-                return false;
-            ObjectOpResult result;
-            if (!DefineProperty(cx, nobj, id, desc, result))
-                return false;
-            MOZ_ASSERT(result.ok());
-        }
-    }
-
-    return true;
-}
-
-/* static */
-UnboxedPlainObject*
-UnboxedPlainObject::create(ExclusiveContext* cx, HandleObjectGroup group, NewObjectKind newKind)
-{
-    AutoSetNewObjectMetadata metadata(cx);
-
-    MOZ_ASSERT(group->clasp() == &class_);
-    gc::AllocKind allocKind = group->unboxedLayout().getAllocKind();
-
-    UnboxedPlainObject* res =
-        NewObjectWithGroup<UnboxedPlainObject>(cx, group, allocKind, newKind);
-    if (!res)
-        return nullptr;
-
-    // Overwrite the dummy shape which was written to the object's expando field.
-    res->initExpando();
-
-    // Initialize reference fields of the object. All fields in the object will
-    // be overwritten shortly, but references need to be safe for the GC.
-    const int32_t* list = res->layout().traceList();
-    if (list) {
-        uint8_t* data = res->data();
-        while (*list != -1) {
-            GCPtrString* heap = reinterpret_cast<GCPtrString*>(data + *list);
-            heap->init(cx->names().empty);
-            list++;
-        }
-        list++;
-        while (*list != -1) {
-            GCPtrObject* heap = reinterpret_cast<GCPtrObject*>(data + *list);
-            heap->init(nullptr);
-            list++;
-        }
-        // Unboxed objects don't have Values to initialize.
-        MOZ_ASSERT(*(list + 1) == -1);
-    }
-
-    return res;
-}
-
-/* static */ JSObject*
-UnboxedPlainObject::createWithProperties(ExclusiveContext* cx, HandleObjectGroup group,
-                                         NewObjectKind newKind, IdValuePair* properties)
-{
-    MOZ_ASSERT(newKind == GenericObject || newKind == TenuredObject);
-
-    UnboxedLayout& layout = group->unboxedLayout();
-
-    if (layout.constructorCode()) {
-        MOZ_ASSERT(cx->isJSContext());
-
-        typedef JSObject* (*ConstructorCodeSignature)(IdValuePair*, NewObjectKind);
-        ConstructorCodeSignature function =
-            reinterpret_cast<ConstructorCodeSignature>(layout.constructorCode()->raw());
-
-        JSObject* obj;
-        {
-            JS::AutoSuppressGCAnalysis nogc;
-            obj = reinterpret_cast<JSObject*>(CALL_GENERATED_2(function, properties, newKind));
-        }
-        if (obj > reinterpret_cast<JSObject*>(CLEAR_CONSTRUCTOR_CODE_TOKEN))
-            return obj;
-
-        if (obj == reinterpret_cast<JSObject*>(CLEAR_CONSTRUCTOR_CODE_TOKEN))
-            layout.setConstructorCode(nullptr);
-    }
-
-    UnboxedPlainObject* obj = UnboxedPlainObject::create(cx, group, newKind);
-    if (!obj)
-        return nullptr;
-
-    for (size_t i = 0; i < layout.properties().length(); i++) {
-        if (!obj->setValue(cx, layout.properties()[i], properties[i].value))
-            return NewPlainObjectWithProperties(cx, properties, layout.properties().length(), newKind);
-    }
-
-#ifndef JS_CODEGEN_NONE
-    if (cx->isJSContext() &&
-        !group->unknownProperties() &&
-        !layout.constructorCode() &&
-        cx->asJSContext()->runtime()->jitSupportsFloatingPoint &&
-        jit::CanLikelyAllocateMoreExecutableMemory())
-    {
-        if (!UnboxedLayout::makeConstructorCode(cx->asJSContext(), group))
-            return nullptr;
-    }
-#endif
-
-    return obj;
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
-                                       HandleId id, MutableHandleObject objp,
-                                       MutableHandleShape propp)
-{
-    if (obj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, id)) {
-        MarkNonNativePropertyFound<CanGC>(propp);
-        objp.set(obj);
-        return true;
-    }
-
-    RootedObject proto(cx, obj->staticPrototype());
-    if (!proto) {
-        objp.set(nullptr);
-        propp.set(nullptr);
-        return true;
-    }
-
-    return LookupProperty(cx, proto, id, objp, propp);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                       Handle<PropertyDescriptor> desc,
-                                       ObjectOpResult& result)
-{
-    const UnboxedLayout& layout = obj->as<UnboxedPlainObject>().layout();
-
-    if (const UnboxedLayout::Property* property = layout.lookup(id)) {
-        if (!desc.getter() && !desc.setter() && desc.attributes() == JSPROP_ENUMERATE) {
-            // This define is equivalent to setting an existing property.
-            if (obj->as<UnboxedPlainObject>().setValue(cx, *property, desc.value()))
-                return result.succeed();
-        }
-
-        // Trying to incompatibly redefine an existing property requires the
-        // object to be converted to a native object.
-        if (!convertToNative(cx, obj))
-            return false;
-
-        return DefineProperty(cx, obj, id, desc, result);
-    }
-
-    // Define the property on the expando object.
-    Rooted<UnboxedExpandoObject*> expando(cx, ensureExpando(cx, obj.as<UnboxedPlainObject>()));
-    if (!expando)
-        return false;
-
-    // Update property types on the unboxed object as well.
-    AddTypePropertyId(cx, obj, id, desc.value());
-
-    return DefineProperty(cx, expando, id, desc, result);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_hasProperty(JSContext* cx, HandleObject obj, HandleId id, bool* foundp)
-{
-    if (obj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, id)) {
-        *foundp = true;
-        return true;
-    }
-
-    RootedObject proto(cx, obj->staticPrototype());
-    if (!proto) {
-        *foundp = false;
-        return true;
-    }
-
-    return HasProperty(cx, proto, id, foundp);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_getProperty(JSContext* cx, HandleObject obj, HandleValue receiver,
-                                    HandleId id, MutableHandleValue vp)
-{
-    const UnboxedLayout& layout = obj->as<UnboxedPlainObject>().layout();
-
-    if (const UnboxedLayout::Property* property = layout.lookup(id)) {
-        vp.set(obj->as<UnboxedPlainObject>().getValue(*property));
-        return true;
-    }
-
-    if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando()) {
-        if (expando->containsShapeOrElement(cx, id)) {
-            RootedObject nexpando(cx, expando);
-            return GetProperty(cx, nexpando, receiver, id, vp);
-        }
-    }
-
-    RootedObject proto(cx, obj->staticPrototype());
-    if (!proto) {
-        vp.setUndefined();
-        return true;
-    }
-
-    return GetProperty(cx, proto, receiver, id, vp);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_setProperty(JSContext* cx, HandleObject obj, HandleId id, HandleValue v,
-                                    HandleValue receiver, ObjectOpResult& result)
-{
-    const UnboxedLayout& layout = obj->as<UnboxedPlainObject>().layout();
-
-    if (const UnboxedLayout::Property* property = layout.lookup(id)) {
-        if (receiver.isObject() && obj == &receiver.toObject()) {
-            if (obj->as<UnboxedPlainObject>().setValue(cx, *property, v))
-                return result.succeed();
-
-            if (!convertToNative(cx, obj))
-                return false;
-            return SetProperty(cx, obj, id, v, receiver, result);
-        }
-
-        return SetPropertyByDefining(cx, id, v, receiver, result);
-    }
-
-    if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando()) {
-        if (expando->containsShapeOrElement(cx, id)) {
-            // Update property types on the unboxed object as well.
-            AddTypePropertyId(cx, obj, id, v);
-
-            RootedObject nexpando(cx, expando);
-            return SetProperty(cx, nexpando, id, v, receiver, result);
-        }
-    }
-
-    return SetPropertyOnProto(cx, obj, id, v, receiver, result);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_getOwnPropertyDescriptor(JSContext* cx, HandleObject obj, HandleId id,
-                                                 MutableHandle<PropertyDescriptor> desc)
-{
-    const UnboxedLayout& layout = obj->as<UnboxedPlainObject>().layout();
-
-    if (const UnboxedLayout::Property* property = layout.lookup(id)) {
-        desc.value().set(obj->as<UnboxedPlainObject>().getValue(*property));
-        desc.setAttributes(JSPROP_ENUMERATE);
-        desc.object().set(obj);
-        return true;
-    }
-
-    if (UnboxedExpandoObject* expando = obj->as<UnboxedPlainObject>().maybeExpando()) {
-        if (expando->containsShapeOrElement(cx, id)) {
-            RootedObject nexpando(cx, expando);
-            if (!GetOwnPropertyDescriptor(cx, nexpando, id, desc))
-                return false;
-            if (desc.object() == nexpando)
-                desc.object().set(obj);
-            return true;
-        }
-    }
-
-    desc.object().set(nullptr);
-    return true;
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_deleteProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                       ObjectOpResult& result)
-{
-    if (!convertToNative(cx, obj))
-        return false;
-    return DeleteProperty(cx, obj, id, result);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_watch(JSContext* cx, HandleObject obj, HandleId id, HandleObject callable)
-{
-    if (!convertToNative(cx, obj))
-        return false;
-    return WatchProperty(cx, obj, id, callable);
-}
-
-/* static */ bool
-UnboxedPlainObject::obj_enumerate(JSContext* cx, HandleObject obj, AutoIdVector& properties,
-                                  bool enumerableOnly)
-{
-    // Ignore expando properties here, they are special-cased by the property
-    // enumeration code.
-
-    const UnboxedLayout::PropertyVector& unboxed = obj->as<UnboxedPlainObject>().layout().properties();
-    for (size_t i = 0; i < unboxed.length(); i++) {
-        if (!properties.append(NameToId(unboxed[i].name)))
-            return false;
-    }
-
-    return true;
-}
-
-const Class UnboxedExpandoObject::class_ = {
-    "UnboxedExpandoObject",
-    0
-};
-
-static const ClassOps UnboxedPlainObjectClassOps = {
-    nullptr,        /* addProperty */
-    nullptr,        /* delProperty */
-    nullptr,        /* getProperty */
-    nullptr,        /* setProperty */
-    nullptr,        /* enumerate   */
-    nullptr,        /* resolve     */
-    nullptr,        /* mayResolve  */
-    nullptr,        /* finalize    */
-    nullptr,        /* call        */
-    nullptr,        /* hasInstance */
-    nullptr,        /* construct   */
-    UnboxedPlainObject::trace,
-};
-
-static const ObjectOps UnboxedPlainObjectObjectOps = {
-    UnboxedPlainObject::obj_lookupProperty,
-    UnboxedPlainObject::obj_defineProperty,
-    UnboxedPlainObject::obj_hasProperty,
-    UnboxedPlainObject::obj_getProperty,
-    UnboxedPlainObject::obj_setProperty,
-    UnboxedPlainObject::obj_getOwnPropertyDescriptor,
-    UnboxedPlainObject::obj_deleteProperty,
-    UnboxedPlainObject::obj_watch,
-    nullptr,   /* No unwatch needed, as watch() converts the object to native */
-    nullptr,   /* getElements */
-    UnboxedPlainObject::obj_enumerate,
-    nullptr    /* funToString */
-};
-
-const Class UnboxedPlainObject::class_ = {
-    js_Object_str,
-    Class::NON_NATIVE |
-    JSCLASS_HAS_CACHED_PROTO(JSProto_Object) |
-    JSCLASS_DELAY_METADATA_BUILDER,
-    &UnboxedPlainObjectClassOps,
-    JS_NULL_CLASS_SPEC,
-    JS_NULL_CLASS_EXT,
-    &UnboxedPlainObjectObjectOps
-};
-
-/////////////////////////////////////////////////////////////////////
-// UnboxedArrayObject
-/////////////////////////////////////////////////////////////////////
-
-template <JSValueType Type>
-DenseElementResult
-AppendUnboxedDenseElements(UnboxedArrayObject* obj, uint32_t initlen,
-                           MutableHandle<GCVector<Value>> values)
-{
-    for (size_t i = 0; i < initlen; i++)
-        values.infallibleAppend(obj->getElementSpecific<Type>(i));
-    return DenseElementResult::Success;
-}
-
-DefineBoxedOrUnboxedFunctor3(AppendUnboxedDenseElements,
-                             UnboxedArrayObject*, uint32_t, MutableHandle<GCVector<Value>>);
-
-/* static */ bool
-UnboxedArrayObject::convertToNativeWithGroup(ExclusiveContext* cx, JSObject* obj,
-                                             ObjectGroup* group, Shape* shape)
-{
-    size_t length = obj->as<UnboxedArrayObject>().length();
-    size_t initlen = obj->as<UnboxedArrayObject>().initializedLength();
-
-    Rooted<GCVector<Value>> values(cx, GCVector<Value>(cx));
-    if (!values.reserve(initlen))
-        return false;
-
-    AppendUnboxedDenseElementsFunctor functor(&obj->as<UnboxedArrayObject>(), initlen, &values);
-    DebugOnly<DenseElementResult> result = CallBoxedOrUnboxedSpecialization(functor, obj);
-    MOZ_ASSERT(result.value == DenseElementResult::Success);
-
-    obj->setGroup(group);
-
-    ArrayObject* aobj = &obj->as<ArrayObject>();
-    aobj->setLastPropertyMakeNative(cx, shape);
-
-    // Make sure there is at least one element, so that this array does not
-    // use emptyObjectElements / emptyObjectElementsShared.
-    if (!aobj->ensureElements(cx, Max<size_t>(initlen, 1)))
-        return false;
-
-    MOZ_ASSERT(!aobj->getDenseInitializedLength());
-    aobj->setDenseInitializedLength(initlen);
-    aobj->initDenseElements(0, values.begin(), initlen);
-    aobj->setLengthInt32(length);
-
-    return true;
-}
-
-/* static */ bool
-UnboxedArrayObject::convertToNative(JSContext* cx, JSObject* obj)
-{
-    const UnboxedLayout& layout = obj->as<UnboxedArrayObject>().layout();
-
-    if (!layout.nativeGroup()) {
-        if (!UnboxedLayout::makeNativeGroup(cx, obj->group()))
-            return false;
-    }
-
-    return convertToNativeWithGroup(cx, obj, layout.nativeGroup(), layout.nativeShape());
-}
-
-bool
-UnboxedArrayObject::convertInt32ToDouble(ExclusiveContext* cx, ObjectGroup* group)
-{
-    MOZ_ASSERT(elementType() == JSVAL_TYPE_INT32);
-    MOZ_ASSERT(group->unboxedLayout().elementType() == JSVAL_TYPE_DOUBLE);
-
-    Vector<int32_t> values(cx);
-    if (!values.reserve(initializedLength()))
-        return false;
-    for (size_t i = 0; i < initializedLength(); i++)
-        values.infallibleAppend(getElementSpecific<JSVAL_TYPE_INT32>(i).toInt32());
-
-    uint8_t* newElements;
-    if (hasInlineElements()) {
-        newElements = AllocateObjectBuffer<uint8_t>(cx, this, capacity() * sizeof(double));
-    } else {
-        newElements = ReallocateObjectBuffer<uint8_t>(cx, this, elements(),
-                                                      capacity() * sizeof(int32_t),
-                                                      capacity() * sizeof(double));
-    }
-    if (!newElements)
-        return false;
-
-    setGroup(group);
-    elements_ = newElements;
-
-    for (size_t i = 0; i < initializedLength(); i++)
-        setElementNoTypeChangeSpecific<JSVAL_TYPE_DOUBLE>(i, DoubleValue(values[i]));
-
-    return true;
-}
-
-/* static */ UnboxedArrayObject*
-UnboxedArrayObject::create(ExclusiveContext* cx, HandleObjectGroup group, uint32_t length,
-                           NewObjectKind newKind, uint32_t maxLength)
-{
-    MOZ_ASSERT(length <= MaximumCapacity);
-
-    MOZ_ASSERT(group->clasp() == &class_);
-    uint32_t elementSize = UnboxedTypeSize(group->unboxedLayout().elementType());
-    uint32_t capacity = Min(length, maxLength);
-    uint32_t nbytes = offsetOfInlineElements() + elementSize * capacity;
-
-    UnboxedArrayObject* res;
-    if (nbytes <= JSObject::MAX_BYTE_SIZE) {
-        gc::AllocKind allocKind = gc::GetGCObjectKindForBytes(nbytes);
-
-        // If there was no provided length information, pick an allocation kind
-        // to accommodate small arrays (as is done for normal native arrays).
-        if (capacity == 0)
-            allocKind = gc::AllocKind::OBJECT8;
-
-        res = NewObjectWithGroup<UnboxedArrayObject>(cx, group, allocKind, newKind);
-        if (!res)
-            return nullptr;
-        res->setInitializedLengthNoBarrier(0);
-        res->setInlineElements();
-
-        size_t actualCapacity = (GetGCKindBytes(allocKind) - offsetOfInlineElements()) / elementSize;
-        MOZ_ASSERT(actualCapacity >= capacity);
-        res->setCapacityIndex(exactCapacityIndex(actualCapacity));
-    } else {
-        res = NewObjectWithGroup<UnboxedArrayObject>(cx, group, gc::AllocKind::OBJECT0, newKind);
-        if (!res)
-            return nullptr;
-        res->setInitializedLengthNoBarrier(0);
-
-        uint32_t capacityIndex = (capacity == length)
-                                 ? CapacityMatchesLengthIndex
-                                 : chooseCapacityIndex(capacity, length);
-        uint32_t actualCapacity = computeCapacity(capacityIndex, length);
-
-        res->elements_ = AllocateObjectBuffer<uint8_t>(cx, res, actualCapacity * elementSize);
-        if (!res->elements_) {
-            // Make the object safe for GC.
-            res->setInlineElements();
-            return nullptr;
-        }
-
-        res->setCapacityIndex(capacityIndex);
-    }
-
-    res->setLength(cx, length);
-    return res;
-}
-
-bool
-UnboxedArrayObject::setElement(ExclusiveContext* cx, size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    uint8_t* p = elements() + index * elementSize();
-    return SetUnboxedValue(cx, this, JSID_VOID, p, elementType(), v, /* preBarrier = */ true);
-}
-
-bool
-UnboxedArrayObject::initElement(ExclusiveContext* cx, size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    uint8_t* p = elements() + index * elementSize();
-    return SetUnboxedValue(cx, this, JSID_VOID, p, elementType(), v, /* preBarrier = */ false);
-}
-
-void
-UnboxedArrayObject::initElementNoTypeChange(size_t index, const Value& v)
-{
-    MOZ_ASSERT(index < initializedLength());
-    uint8_t* p = elements() + index * elementSize();
-    if (UnboxedTypeNeedsPreBarrier(elementType()))
-        *reinterpret_cast<void**>(p) = nullptr;
-    SetUnboxedValueNoTypeChange(this, p, elementType(), v, /* preBarrier = */ false);
-}
-
-Value
-UnboxedArrayObject::getElement(size_t index)
-{
-    MOZ_ASSERT(index < initializedLength());
-    uint8_t* p = elements() + index * elementSize();
-    return GetUnboxedValue(p, elementType(), /* maybeUninitialized = */ false);
-}
-
-/* static */ void
-UnboxedArrayObject::trace(JSTracer* trc, JSObject* obj)
-{
-    JSValueType type = obj->as<UnboxedArrayObject>().elementType();
-    if (!UnboxedTypeNeedsPreBarrier(type))
-        return;
-
-    MOZ_ASSERT(obj->as<UnboxedArrayObject>().elementSize() == sizeof(uintptr_t));
-    size_t initlen = obj->as<UnboxedArrayObject>().initializedLength();
-    void** elements = reinterpret_cast<void**>(obj->as<UnboxedArrayObject>().elements());
-
-    switch (type) {
-      case JSVAL_TYPE_OBJECT:
-        for (size_t i = 0; i < initlen; i++) {
-            GCPtrObject* heap = reinterpret_cast<GCPtrObject*>(elements + i);
-            TraceNullableEdge(trc, heap, "unboxed_object");
-        }
-        break;
-
-      case JSVAL_TYPE_STRING:
-        for (size_t i = 0; i < initlen; i++) {
-            GCPtrString* heap = reinterpret_cast<GCPtrString*>(elements + i);
-            TraceEdge(trc, heap, "unboxed_string");
-        }
-        break;
-
-      default:
-        MOZ_CRASH();
-    }
-}
-
-/* static */ void
-UnboxedArrayObject::objectMoved(JSObject* obj, const JSObject* old)
-{
-    UnboxedArrayObject& dst = obj->as<UnboxedArrayObject>();
-    const UnboxedArrayObject& src = old->as<UnboxedArrayObject>();
-
-    // Fix up possible inline data pointer.
-    if (src.hasInlineElements())
-        dst.setInlineElements();
-}
-
-/* static */ void
-UnboxedArrayObject::finalize(FreeOp* fop, JSObject* obj)
-{
-    MOZ_ASSERT(!IsInsideNursery(obj));
-    if (!obj->as<UnboxedArrayObject>().hasInlineElements())
-        js_free(obj->as<UnboxedArrayObject>().elements());
-}
-
-/* static */ size_t
-UnboxedArrayObject::objectMovedDuringMinorGC(JSTracer* trc, JSObject* dst, JSObject* src,
-                                             gc::AllocKind allocKind)
-{
-    UnboxedArrayObject* ndst = &dst->as<UnboxedArrayObject>();
-    UnboxedArrayObject* nsrc = &src->as<UnboxedArrayObject>();
-    MOZ_ASSERT(ndst->elements() == nsrc->elements());
-
-    Nursery& nursery = trc->runtime()->gc.nursery;
-
-    if (!nursery.isInside(nsrc->elements())) {
-        nursery.removeMallocedBuffer(nsrc->elements());
-        return 0;
-    }
-
-    // Determine if we can use inline data for the target array. If this is
-    // possible, the nursery will have picked an allocation size that is large
-    // enough.
-    size_t nbytes = nsrc->capacity() * nsrc->elementSize();
-    if (offsetOfInlineElements() + nbytes <= GetGCKindBytes(allocKind)) {
-        ndst->setInlineElements();
-    } else {
-        MOZ_ASSERT(allocKind == gc::AllocKind::OBJECT0);
-
-        AutoEnterOOMUnsafeRegion oomUnsafe;
-        uint8_t* data = nsrc->zone()->pod_malloc<uint8_t>(nbytes);
-        if (!data)
-            oomUnsafe.crash("Failed to allocate unboxed array elements while tenuring.");
-        ndst->elements_ = data;
-    }
-
-    PodCopy(ndst->elements(), nsrc->elements(), nsrc->initializedLength() * nsrc->elementSize());
-
-    // Set a forwarding pointer for the element buffers in case they were
-    // preserved on the stack by Ion.
-    bool direct = nsrc->capacity() * nsrc->elementSize() >= sizeof(uintptr_t);
-    nursery.maybeSetForwardingPointer(trc, nsrc->elements(), ndst->elements(), direct);
-
-    return ndst->hasInlineElements() ? 0 : nbytes;
-}
-
-// Possible capacities for unboxed arrays. Some of these capacities might seem
-// a little weird, but were chosen to allow the inline data of objects of each
-// size to be fully utilized for arrays of the various types on both 32 bit and
-// 64 bit platforms.
-//
-// To find the possible inline capacities, the following script was used:
-//
-// var fixedSlotCapacities = [0, 2, 4, 8, 12, 16];
-// var dataSizes = [1, 4, 8];
-// var header32 = 4 * 2 + 4 * 2;
-// var header64 = 8 * 2 + 4 * 2;
-//
-// for (var i = 0; i < fixedSlotCapacities.length; i++) {
-//    var nfixed = fixedSlotCapacities[i];
-//    var size32 = 4 * 4 + 8 * nfixed - header32;
-//    var size64 = 8 * 4 + 8 * nfixed - header64;
-//    for (var j = 0; j < dataSizes.length; j++) {
-//        print(size32 / dataSizes[j]);
-//        print(size64 / dataSizes[j]);
-//    }
-// }
-//
-/* static */ const uint32_t
-UnboxedArrayObject::CapacityArray[] = {
-    UINT32_MAX, // For CapacityMatchesLengthIndex.
-    0, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 13, 16, 17, 18, 24, 26, 32, 34, 40, 64, 72, 96, 104, 128, 136,
-    256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288,
-    1048576, 2097152, 3145728, 4194304, 5242880, 6291456, 7340032, 8388608, 9437184, 11534336,
-    13631488, 15728640, 17825792, 20971520, 24117248, 27262976, 31457280, 35651584, 40894464,
-    46137344, 52428800, 59768832, MaximumCapacity
-};
-
-static const uint32_t
-Pow2CapacityIndexes[] = {
-    2,  // 1
-    3,  // 2
-    5,  // 4
-    8,  // 8
-    13, // 16
-    18, // 32
-    21, // 64
-    25, // 128
-    27, // 256
-    28, // 512
-    29, // 1024
-    30, // 2048
-    31, // 4096
-    32, // 8192
-    33, // 16384
-    34, // 32768
-    35, // 65536
-    36, // 131072
-    37, // 262144
-    38, // 524288
-    39  // 1048576
-};
-
-static const uint32_t MebiCapacityIndex = 39;
-
-/* static */ uint32_t
-UnboxedArrayObject::chooseCapacityIndex(uint32_t capacity, uint32_t length)
-{
-    // Note: the structure and behavior of this method follow along with
-    // NativeObject::goodAllocated. Changes to the allocation strategy in one
-    // should generally be matched by the other.
-
-    // Make sure we have enough space to store all possible values for the capacity index.
-    // This ought to be a static_assert, but MSVC doesn't like that.
-    MOZ_ASSERT(mozilla::ArrayLength(CapacityArray) - 1 <= (CapacityMask >> CapacityShift));
-
-    // The caller should have ensured the capacity is possible for an unboxed array.
-    MOZ_ASSERT(capacity <= MaximumCapacity);
-
-    static const uint32_t Mebi = 1024 * 1024;
-
-    if (capacity <= Mebi) {
-        capacity = mozilla::RoundUpPow2(capacity);
-
-        // When the required capacity is close to the array length, then round
-        // up to the array length itself, as for NativeObject.
-        if (length >= capacity && capacity > (length / 3) * 2)
-            return CapacityMatchesLengthIndex;
-
-        if (capacity < MinimumDynamicCapacity)
-            capacity = MinimumDynamicCapacity;
-
-        uint32_t bit = mozilla::FloorLog2Size(capacity);
-        MOZ_ASSERT(capacity == uint32_t(1 << bit));
-        MOZ_ASSERT(bit <= 20);
-        MOZ_ASSERT(mozilla::ArrayLength(Pow2CapacityIndexes) == 21);
-
-        uint32_t index = Pow2CapacityIndexes[bit];
-        MOZ_ASSERT(CapacityArray[index] == capacity);
-
-        return index;
-    }
-
-    MOZ_ASSERT(CapacityArray[MebiCapacityIndex] == Mebi);
-
-    for (uint32_t i = MebiCapacityIndex + 1;; i++) {
-        if (CapacityArray[i] >= capacity)
-            return i;
-    }
-
-    MOZ_CRASH("Invalid capacity");
-}
-
-/* static */ uint32_t
-UnboxedArrayObject::exactCapacityIndex(uint32_t capacity)
-{
-    for (size_t i = CapacityMatchesLengthIndex + 1; i < ArrayLength(CapacityArray); i++) {
-        if (CapacityArray[i] == capacity)
-            return i;
-    }
-    MOZ_CRASH();
-}
-
-bool
-UnboxedArrayObject::growElements(ExclusiveContext* cx, size_t cap)
-{
-    // The caller should have checked if this capacity is possible for an
-    // unboxed array, so the only way this call can fail is from OOM.
-    MOZ_ASSERT(cap <= MaximumCapacity);
-
-    uint32_t oldCapacity = capacity();
-    uint32_t newCapacityIndex = chooseCapacityIndex(cap, length());
-    uint32_t newCapacity = computeCapacity(newCapacityIndex, length());
-
-    MOZ_ASSERT(oldCapacity < cap);
-    MOZ_ASSERT(cap <= newCapacity);
-
-    // The allocation size computation below cannot have integer overflows.
-    JS_STATIC_ASSERT(MaximumCapacity < UINT32_MAX / sizeof(double));
-
-    uint8_t* newElements;
-    if (hasInlineElements()) {
-        newElements = AllocateObjectBuffer<uint8_t>(cx, this, newCapacity * elementSize());
-        if (!newElements)
-            return false;
-        js_memcpy(newElements, elements(), initializedLength() * elementSize());
-    } else {
-        newElements = ReallocateObjectBuffer<uint8_t>(cx, this, elements(),
-                                                      oldCapacity * elementSize(),
-                                                      newCapacity * elementSize());
-        if (!newElements)
-            return false;
-    }
-
-    elements_ = newElements;
-    setCapacityIndex(newCapacityIndex);
-
-    return true;
-}
-
-void
-UnboxedArrayObject::shrinkElements(ExclusiveContext* cx, size_t cap)
-{
-    if (hasInlineElements())
-        return;
-
-    uint32_t oldCapacity = capacity();
-    uint32_t newCapacityIndex = chooseCapacityIndex(cap, 0);
-    uint32_t newCapacity = computeCapacity(newCapacityIndex, 0);
-
-    MOZ_ASSERT(cap < oldCapacity);
-    MOZ_ASSERT(cap <= newCapacity);
-
-    if (newCapacity >= oldCapacity)
-        return;
-
-    uint8_t* newElements = ReallocateObjectBuffer<uint8_t>(cx, this, elements(),
-                                                           oldCapacity * elementSize(),
-                                                           newCapacity * elementSize());
-    if (!newElements)
-        return;
-
-    elements_ = newElements;
-    setCapacityIndex(newCapacityIndex);
-}
-
-bool
-UnboxedArrayObject::containsProperty(ExclusiveContext* cx, jsid id)
-{
-    if (JSID_IS_INT(id) && uint32_t(JSID_TO_INT(id)) < initializedLength())
-        return true;
-    if (JSID_IS_ATOM(id) && JSID_TO_ATOM(id) == cx->names().length)
-        return true;
-    return false;
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_lookupProperty(JSContext* cx, HandleObject obj,
-                                       HandleId id, MutableHandleObject objp,
-                                       MutableHandleShape propp)
-{
-    if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        MarkNonNativePropertyFound<CanGC>(propp);
-        objp.set(obj);
-        return true;
-    }
-
-    RootedObject proto(cx, obj->staticPrototype());
-    if (!proto) {
-        objp.set(nullptr);
-        propp.set(nullptr);
-        return true;
-    }
-
-    return LookupProperty(cx, proto, id, objp, propp);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                       Handle<PropertyDescriptor> desc,
-                                       ObjectOpResult& result)
-{
-    if (JSID_IS_INT(id) && !desc.getter() && !desc.setter() && desc.attributes() == JSPROP_ENUMERATE) {
-        UnboxedArrayObject* nobj = &obj->as<UnboxedArrayObject>();
-
-        uint32_t index = JSID_TO_INT(id);
-        if (index < nobj->initializedLength()) {
-            if (nobj->setElement(cx, index, desc.value()))
-                return result.succeed();
-        } else if (index == nobj->initializedLength() && index < MaximumCapacity) {
-            if (nobj->initializedLength() == nobj->capacity()) {
-                if (!nobj->growElements(cx, index + 1))
-                    return false;
-            }
-            nobj->setInitializedLength(index + 1);
-            if (nobj->initElement(cx, index, desc.value())) {
-                if (nobj->length() <= index)
-                    nobj->setLengthInt32(index + 1);
-                return result.succeed();
-            }
-            nobj->setInitializedLengthNoBarrier(index);
-        }
-    }
-
-    if (!convertToNative(cx, obj))
-        return false;
-
-    return DefineProperty(cx, obj, id, desc, result);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_hasProperty(JSContext* cx, HandleObject obj, HandleId id, bool* foundp)
-{
-    if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        *foundp = true;
-        return true;
-    }
-
-    RootedObject proto(cx, obj->staticPrototype());
-    if (!proto) {
-        *foundp = false;
-        return true;
-    }
-
-    return HasProperty(cx, proto, id, foundp);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_getProperty(JSContext* cx, HandleObject obj, HandleValue receiver,
-                                    HandleId id, MutableHandleValue vp)
-{
-    if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        if (JSID_IS_INT(id))
-            vp.set(obj->as<UnboxedArrayObject>().getElement(JSID_TO_INT(id)));
-        else
-            vp.set(Int32Value(obj->as<UnboxedArrayObject>().length()));
-        return true;
-    }
-
-    RootedObject proto(cx, obj->staticPrototype());
-    if (!proto) {
-        vp.setUndefined();
-        return true;
-    }
-
-    return GetProperty(cx, proto, receiver, id, vp);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_setProperty(JSContext* cx, HandleObject obj, HandleId id, HandleValue v,
-                                    HandleValue receiver, ObjectOpResult& result)
-{
-    if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        if (receiver.isObject() && obj == &receiver.toObject()) {
-            if (JSID_IS_INT(id)) {
-                if (obj->as<UnboxedArrayObject>().setElement(cx, JSID_TO_INT(id), v))
-                    return result.succeed();
-            } else {
-                uint32_t len;
-                if (!CanonicalizeArrayLengthValue(cx, v, &len))
-                    return false;
-                UnboxedArrayObject* nobj = &obj->as<UnboxedArrayObject>();
-                if (len < nobj->initializedLength()) {
-                    nobj->setInitializedLength(len);
-                    nobj->shrinkElements(cx, len);
-                }
-                nobj->setLength(cx, len);
-                return result.succeed();
-            }
-
-            if (!convertToNative(cx, obj))
-                return false;
-            return SetProperty(cx, obj, id, v, receiver, result);
-        }
-
-        return SetPropertyByDefining(cx, id, v, receiver, result);
-    }
-
-    return SetPropertyOnProto(cx, obj, id, v, receiver, result);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_getOwnPropertyDescriptor(JSContext* cx, HandleObject obj, HandleId id,
-                                                 MutableHandle<PropertyDescriptor> desc)
-{
-    if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        if (JSID_IS_INT(id)) {
-            desc.value().set(obj->as<UnboxedArrayObject>().getElement(JSID_TO_INT(id)));
-            desc.setAttributes(JSPROP_ENUMERATE);
-        } else {
-            desc.value().set(Int32Value(obj->as<UnboxedArrayObject>().length()));
-            desc.setAttributes(JSPROP_PERMANENT);
-        }
-        desc.object().set(obj);
-        return true;
-    }
-
-    desc.object().set(nullptr);
-    return true;
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_deleteProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                       ObjectOpResult& result)
-{
-    if (obj->as<UnboxedArrayObject>().containsProperty(cx, id)) {
-        size_t initlen = obj->as<UnboxedArrayObject>().initializedLength();
-        if (JSID_IS_INT(id) && JSID_TO_INT(id) == int32_t(initlen - 1)) {
-            obj->as<UnboxedArrayObject>().setInitializedLength(initlen - 1);
-            obj->as<UnboxedArrayObject>().shrinkElements(cx, initlen - 1);
-            return result.succeed();
-        }
-    }
-
-    if (!convertToNative(cx, obj))
-        return false;
-    return DeleteProperty(cx, obj, id, result);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_watch(JSContext* cx, HandleObject obj, HandleId id, HandleObject callable)
-{
-    if (!convertToNative(cx, obj))
-        return false;
-    return WatchProperty(cx, obj, id, callable);
-}
-
-/* static */ bool
-UnboxedArrayObject::obj_enumerate(JSContext* cx, HandleObject obj, AutoIdVector& properties,
-                                  bool enumerableOnly)
-{
-    for (size_t i = 0; i < obj->as<UnboxedArrayObject>().initializedLength(); i++) {
-        if (!properties.append(INT_TO_JSID(i)))
-            return false;
-    }
-
-    if (!enumerableOnly && !properties.append(NameToId(cx->names().length)))
-        return false;
-
-    return true;
-}
-
-static const ClassOps UnboxedArrayObjectClassOps = {
-    nullptr,        /* addProperty */
-    nullptr,        /* delProperty */
-    nullptr,        /* getProperty */
-    nullptr,        /* setProperty */
-    nullptr,        /* enumerate   */
-    nullptr,        /* resolve     */
-    nullptr,        /* mayResolve  */
-    UnboxedArrayObject::finalize,
-    nullptr,        /* call        */
-    nullptr,        /* hasInstance */
-    nullptr,        /* construct   */
-    UnboxedArrayObject::trace,
-};
-
-static const ClassExtension UnboxedArrayObjectClassExtension = {
-    nullptr,    /* weakmapKeyDelegateOp */
-    UnboxedArrayObject::objectMoved
-};
-
-static const ObjectOps UnboxedArrayObjectObjectOps = {
-    UnboxedArrayObject::obj_lookupProperty,
-    UnboxedArrayObject::obj_defineProperty,
-    UnboxedArrayObject::obj_hasProperty,
-    UnboxedArrayObject::obj_getProperty,
-    UnboxedArrayObject::obj_setProperty,
-    UnboxedArrayObject::obj_getOwnPropertyDescriptor,
-    UnboxedArrayObject::obj_deleteProperty,
-    UnboxedArrayObject::obj_watch,
-    nullptr,   /* No unwatch needed, as watch() converts the object to native */
-    nullptr,   /* getElements */
-    UnboxedArrayObject::obj_enumerate,
-    nullptr    /* funToString */
-};
-
-const Class UnboxedArrayObject::class_ = {
-    "Array",
-    Class::NON_NATIVE |
-    JSCLASS_SKIP_NURSERY_FINALIZE |
-    JSCLASS_BACKGROUND_FINALIZE,
-    &UnboxedArrayObjectClassOps,
-    JS_NULL_CLASS_SPEC,
-    &UnboxedArrayObjectClassExtension,
-    &UnboxedArrayObjectObjectOps
-};
-
-/////////////////////////////////////////////////////////////////////
-// API
-/////////////////////////////////////////////////////////////////////
-
-static bool
-UnboxedTypeIncludes(JSValueType supertype, JSValueType subtype)
-{
-    if (supertype == JSVAL_TYPE_DOUBLE && subtype == JSVAL_TYPE_INT32)
-        return true;
-    if (supertype == JSVAL_TYPE_OBJECT && subtype == JSVAL_TYPE_NULL)
-        return true;
-    return false;
-}
-
-static bool
-CombineUnboxedTypes(const Value& value, JSValueType* existing)
-{
-    JSValueType type = value.isDouble() ? JSVAL_TYPE_DOUBLE : value.extractNonDoubleType();
-
-    if (*existing == JSVAL_TYPE_MAGIC || *existing == type || UnboxedTypeIncludes(type, *existing)) {
-        *existing = type;
-        return true;
-    }
-    if (UnboxedTypeIncludes(*existing, type))
-        return true;
-    return false;
-}
-
-// Return whether the property names and types in layout are a subset of the
-// specified vector.
-static bool
-PropertiesAreSuperset(const UnboxedLayout::PropertyVector& properties, UnboxedLayout* layout)
-{
-    for (size_t i = 0; i < layout->properties().length(); i++) {
-        const UnboxedLayout::Property& layoutProperty = layout->properties()[i];
-        bool found = false;
-        for (size_t j = 0; j < properties.length(); j++) {
-            if (layoutProperty.name == properties[j].name) {
-                found = (layoutProperty.type == properties[j].type);
-                break;
-            }
-        }
-        if (!found)
-            return false;
-    }
-    return true;
-}
-
-static bool
-CombinePlainObjectProperties(PlainObject* obj, Shape* templateShape,
-                             UnboxedLayout::PropertyVector& properties)
-{
-    // All preliminary objects must have been created with enough space to
-    // fill in their unboxed data inline. This is ensured either by using
-    // the largest allocation kind (which limits the maximum size of an
-    // unboxed object), or by using an allocation kind that covers all
-    // properties in the template, as the space used by unboxed properties
-    // is less than or equal to that used by boxed properties.
-    MOZ_ASSERT(gc::GetGCKindSlots(obj->asTenured().getAllocKind()) >=
-               Min(NativeObject::MAX_FIXED_SLOTS, templateShape->slotSpan()));
-
-    if (obj->lastProperty() != templateShape || obj->hasDynamicElements()) {
-        // Only use an unboxed representation if all created objects match
-        // the template shape exactly.
-        return false;
-    }
-
-    for (size_t i = 0; i < templateShape->slotSpan(); i++) {
-        Value val = obj->getSlot(i);
-
-        JSValueType& existing = properties[i].type;
-        if (!CombineUnboxedTypes(val, &existing))
-            return false;
-    }
-
-    return true;
-}
-
-static bool
-CombineArrayObjectElements(ExclusiveContext* cx, ArrayObject* obj, JSValueType* elementType)
-{
-    if (obj->inDictionaryMode() ||
-        obj->lastProperty()->propid() != AtomToId(cx->names().length) ||
-        !obj->lastProperty()->previous()->isEmptyShape())
-    {
-        // Only use an unboxed representation if the object has no properties.
-        return false;
-    }
-
-    for (size_t i = 0; i < obj->getDenseInitializedLength(); i++) {
-        Value val = obj->getDenseElement(i);
-
-        // For now, unboxed arrays cannot have holes.
-        if (val.isMagic(JS_ELEMENTS_HOLE))
-            return false;
-
-        if (!CombineUnboxedTypes(val, elementType))
-            return false;
-    }
-
-    return true;
-}
-
-static size_t
-ComputePlainObjectLayout(ExclusiveContext* cx, Shape* templateShape,
-                         UnboxedLayout::PropertyVector& properties)
-{
-    // Fill in the names for all the object's properties.
-    for (Shape::Range<NoGC> r(templateShape); !r.empty(); r.popFront()) {
-        size_t slot = r.front().slot();
-        MOZ_ASSERT(!properties[slot].name);
-        properties[slot].name = JSID_TO_ATOM(r.front().propid())->asPropertyName();
-    }
-
-    // Fill in all the unboxed object's property offsets.
-    uint32_t offset = 0;
-
-    // Search for an existing unboxed layout which is a subset of this one.
-    // If there are multiple such layouts, use the largest one. If we're able
-    // to find such a layout, use the same property offsets for the shared
-    // properties, which will allow us to generate better code if the objects
-    // have a subtype/supertype relation and are accessed at common sites.
-    UnboxedLayout* bestExisting = nullptr;
-    for (UnboxedLayout* existing : cx->compartment()->unboxedLayouts) {
-        if (PropertiesAreSuperset(properties, existing)) {
-            if (!bestExisting ||
-                existing->properties().length() > bestExisting->properties().length())
-            {
-                bestExisting = existing;
-            }
-        }
-    }
-    if (bestExisting) {
-        for (size_t i = 0; i < bestExisting->properties().length(); i++) {
-            const UnboxedLayout::Property& existingProperty = bestExisting->properties()[i];
-            for (size_t j = 0; j < templateShape->slotSpan(); j++) {
-                if (existingProperty.name == properties[j].name) {
-                    MOZ_ASSERT(existingProperty.type == properties[j].type);
-                    properties[j].offset = existingProperty.offset;
-                }
-            }
-        }
-        offset = bestExisting->size();
-    }
-
-    // Order remaining properties from the largest down for the best space
-    // utilization.
-    static const size_t typeSizes[] = { 8, 4, 1 };
-
-    for (size_t i = 0; i < ArrayLength(typeSizes); i++) {
-        size_t size = typeSizes[i];
-        for (size_t j = 0; j < templateShape->slotSpan(); j++) {
-            if (properties[j].offset != UINT32_MAX)
-                continue;
-            JSValueType type = properties[j].type;
-            if (UnboxedTypeSize(type) == size) {
-                offset = JS_ROUNDUP(offset, size);
-                properties[j].offset = offset;
-                offset += size;
-            }
-        }
-    }
-
-    // The final offset is the amount of data needed by the object.
-    return offset;
-}
-
-static bool
-SetLayoutTraceList(ExclusiveContext* cx, UnboxedLayout* layout)
-{
-    // Figure out the offsets of any objects or string properties.
-    Vector<int32_t, 8, SystemAllocPolicy> objectOffsets, stringOffsets;
-    for (size_t i = 0; i < layout->properties().length(); i++) {
-        const UnboxedLayout::Property& property = layout->properties()[i];
-        MOZ_ASSERT(property.offset != UINT32_MAX);
-        if (property.type == JSVAL_TYPE_OBJECT) {
-            if (!objectOffsets.append(property.offset))
-                return false;
-        } else if (property.type == JSVAL_TYPE_STRING) {
-            if (!stringOffsets.append(property.offset))
-                return false;
-        }
-    }
-
-    // Construct the layout's trace list.
-    if (!objectOffsets.empty() || !stringOffsets.empty()) {
-        Vector<int32_t, 8, SystemAllocPolicy> entries;
-        if (!entries.appendAll(stringOffsets) ||
-            !entries.append(-1) ||
-            !entries.appendAll(objectOffsets) ||
-            !entries.append(-1) ||
-            !entries.append(-1))
-        {
-            return false;
-        }
-        int32_t* traceList = cx->zone()->pod_malloc<int32_t>(entries.length());
-        if (!traceList)
-            return false;
-        PodCopy(traceList, entries.begin(), entries.length());
-        layout->setTraceList(traceList);
-    }
-
-    return true;
-}
-
-static inline Value
-NextValue(Handle<GCVector<Value>> values, size_t* valueCursor)
-{
-    return values[(*valueCursor)++];
-}
-
-static bool
-GetValuesFromPreliminaryArrayObject(ArrayObject* obj, MutableHandle<GCVector<Value>> values)
-{
-    if (!values.append(Int32Value(obj->length())))
-        return false;
-    if (!values.append(Int32Value(obj->getDenseInitializedLength())))
-        return false;
-    for (size_t i = 0; i < obj->getDenseInitializedLength(); i++) {
-        if (!values.append(obj->getDenseElement(i)))
-            return false;
-    }
-    return true;
-}
-
-void
-UnboxedArrayObject::fillAfterConvert(ExclusiveContext* cx,
-                                     Handle<GCVector<Value>> values, size_t* valueCursor)
-{
-    MOZ_ASSERT(CapacityArray[1] == 0);
-    setCapacityIndex(1);
-    setInitializedLengthNoBarrier(0);
-    setInlineElements();
-
-    setLength(cx, NextValue(values, valueCursor).toInt32());
-
-    int32_t initlen = NextValue(values, valueCursor).toInt32();
-    if (!initlen)
-        return;
-
-    AutoEnterOOMUnsafeRegion oomUnsafe;
-    if (!growElements(cx, initlen))
-        oomUnsafe.crash("UnboxedArrayObject::fillAfterConvert");
-
-    setInitializedLength(initlen);
-
-    for (size_t i = 0; i < size_t(initlen); i++)
-        JS_ALWAYS_TRUE(initElement(cx, i, NextValue(values, valueCursor)));
-}
-
-static bool
-GetValuesFromPreliminaryPlainObject(PlainObject* obj, MutableHandle<GCVector<Value>> values)
-{
-    for (size_t i = 0; i < obj->slotSpan(); i++) {
-        if (!values.append(obj->getSlot(i)))
-            return false;
-    }
-    return true;
-}
-
-void
-UnboxedPlainObject::fillAfterConvert(ExclusiveContext* cx,
-                                     Handle<GCVector<Value>> values, size_t* valueCursor)
-{
-    initExpando();
-    memset(data(), 0, layout().size());
-    for (size_t i = 0; i < layout().properties().length(); i++)
-        JS_ALWAYS_TRUE(setValue(cx, layout().properties()[i], NextValue(values, valueCursor)));
-}
-
-bool
-js::TryConvertToUnboxedLayout(ExclusiveContext* cx, AutoEnterAnalysis& enter, Shape* templateShape,
-                              ObjectGroup* group, PreliminaryObjectArray* objects)
-{
-    bool isArray = !templateShape;
-
-    // Unboxed arrays are nightly only for now. The getenv() call will be
-    // removed when they are on by default. See bug 1153266.
-    if (isArray) {
-#ifdef NIGHTLY_BUILD
-        if (!getenv("JS_OPTION_USE_UNBOXED_ARRAYS")) {
-            if (!cx->options().unboxedArrays())
-                return true;
-        }
-#else
-        return true;
-#endif
-    } else {
-        if (jit::JitOptions.disableUnboxedObjects)
-            return true;
-    }
-
-    MOZ_ASSERT_IF(templateShape, !templateShape->getObjectFlags());
-
-    if (group->runtimeFromAnyThread()->isSelfHostingGlobal(cx->global()))
-        return true;
-
-    if (!isArray && templateShape->slotSpan() == 0)
-        return true;
-
-    UnboxedLayout::PropertyVector properties;
-    if (!isArray) {
-        if (!properties.appendN(UnboxedLayout::Property(), templateShape->slotSpan()))
-            return false;
-    }
-    JSValueType elementType = JSVAL_TYPE_MAGIC;
-
-    size_t objectCount = 0;
-    for (size_t i = 0; i < PreliminaryObjectArray::COUNT; i++) {
-        JSObject* obj = objects->get(i);
-        if (!obj)
-            continue;
-
-        if (obj->isSingleton() || obj->group() != group)
-            return true;
-
-        objectCount++;
-
-        if (isArray) {
-            if (!CombineArrayObjectElements(cx, &obj->as<ArrayObject>(), &elementType))
-                return true;
-        } else {
-            if (!CombinePlainObjectProperties(&obj->as<PlainObject>(), templateShape, properties))
-                return true;
-        }
-    }
-
-    size_t layoutSize = 0;
-    if (isArray) {
-        // Don't use an unboxed representation if we couldn't determine an
-        // element type for the objects.
-        if (UnboxedTypeSize(elementType) == 0)
-            return true;
-    } else {
-        if (objectCount <= 1) {
-            // If only one of the objects has been created, it is more likely
-            // to have new properties added later. This heuristic is not used
-            // for array objects, where we might want an unboxed representation
-            // even if there is only one large array.
-            return true;
-        }
-
-        for (size_t i = 0; i < templateShape->slotSpan(); i++) {
-            // We can't use an unboxed representation if e.g. all the objects have
-            // a null value for one of the properties, as we can't decide what type
-            // it is supposed to have.
-            if (UnboxedTypeSize(properties[i].type) == 0)
-                return true;
-        }
-
-        // Make sure that all properties on the template shape are property
-        // names, and not indexes.
-        for (Shape::Range<NoGC> r(templateShape); !r.empty(); r.popFront()) {
-            jsid id = r.front().propid();
-            uint32_t dummy;
-            if (!JSID_IS_ATOM(id) || JSID_TO_ATOM(id)->isIndex(&dummy))
-                return true;
-        }
-
-        layoutSize = ComputePlainObjectLayout(cx, templateShape, properties);
-
-        // The entire object must be allocatable inline.
-        if (UnboxedPlainObject::offsetOfData() + layoutSize > JSObject::MAX_BYTE_SIZE)
-            return true;
-    }
-
-    UniquePtr<UnboxedLayout>& layout = enter.unboxedLayoutToCleanUp;
-    MOZ_ASSERT(!layout);
-    layout = group->zone()->make_unique<UnboxedLayout>();
-    if (!layout)
-        return false;
-
-    if (isArray) {
-        layout->initArray(elementType);
-    } else {
-        if (!layout->initProperties(properties, layoutSize))
-            return false;
-
-        // The unboxedLayouts list only tracks layouts for plain objects.
-        cx->compartment()->unboxedLayouts.insertFront(layout.get());
-
-        if (!SetLayoutTraceList(cx, layout.get()))
-            return false;
-    }
-
-    // We've determined that all the preliminary objects can use the new layout
-    // just constructed, so convert the existing group to use the unboxed class,
-    // and update the preliminary objects to use the new layout. Do the
-    // fallible stuff first before modifying any objects.
-
-    // Get an empty shape which we can use for the preliminary objects.
-    const Class* clasp = isArray ? &UnboxedArrayObject::class_ : &UnboxedPlainObject::class_;
-    Shape* newShape = EmptyShape::getInitialShape(cx, clasp, group->proto(), 0);
-    if (!newShape) {
-        cx->recoverFromOutOfMemory();
-        return false;
-    }
-
-    // Accumulate a list of all the values in each preliminary object, and
-    // update their shapes.
-    Rooted<GCVector<Value>> values(cx, GCVector<Value>(cx));
-    for (size_t i = 0; i < PreliminaryObjectArray::COUNT; i++) {
-        JSObject* obj = objects->get(i);
-        if (!obj)
-            continue;
-
-        bool ok;
-        if (isArray)
-            ok = GetValuesFromPreliminaryArrayObject(&obj->as<ArrayObject>(), &values);
-        else
-            ok = GetValuesFromPreliminaryPlainObject(&obj->as<PlainObject>(), &values);
-
-        if (!ok) {
-            cx->recoverFromOutOfMemory();
-            return false;
-        }
-    }
-
-    if (TypeNewScript* newScript = group->newScript())
-        layout->setNewScript(newScript);
-
-    for (size_t i = 0; i < PreliminaryObjectArray::COUNT; i++) {
-        if (JSObject* obj = objects->get(i))
-            obj->as<NativeObject>().setLastPropertyMakeNonNative(newShape);
-    }
-
-    group->setClasp(clasp);
-    group->setUnboxedLayout(layout.release());
-
-    size_t valueCursor = 0;
-    for (size_t i = 0; i < PreliminaryObjectArray::COUNT; i++) {
-        JSObject* obj = objects->get(i);
-        if (!obj)
-            continue;
-
-        if (isArray)
-            obj->as<UnboxedArrayObject>().fillAfterConvert(cx, values, &valueCursor);
-        else
-            obj->as<UnboxedPlainObject>().fillAfterConvert(cx, values, &valueCursor);
-    }
-
-    MOZ_ASSERT(valueCursor == values.length());
-    return true;
-}
-
-DefineBoxedOrUnboxedFunctor6(SetOrExtendBoxedOrUnboxedDenseElements,
-                             ExclusiveContext*, JSObject*, uint32_t, const Value*, uint32_t,
-                             ShouldUpdateTypes);
-
-DenseElementResult
-js::SetOrExtendAnyBoxedOrUnboxedDenseElements(ExclusiveContext* cx, JSObject* obj,
-                                              uint32_t start, const Value* vp, uint32_t count,
-                                              ShouldUpdateTypes updateTypes)
-{
-    SetOrExtendBoxedOrUnboxedDenseElementsFunctor functor(cx, obj, start, vp, count, updateTypes);
-    return CallBoxedOrUnboxedSpecialization(functor, obj);
-};
-
-DefineBoxedOrUnboxedFunctor5(MoveBoxedOrUnboxedDenseElements,
-                             JSContext*, JSObject*, uint32_t, uint32_t, uint32_t);
-
-DenseElementResult
-js::MoveAnyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* obj,
-                                       uint32_t dstStart, uint32_t srcStart, uint32_t length)
-{
-    MoveBoxedOrUnboxedDenseElementsFunctor functor(cx, obj, dstStart, srcStart, length);
-    return CallBoxedOrUnboxedSpecialization(functor, obj);
-}
-
-DefineBoxedOrUnboxedFunctorPair6(CopyBoxedOrUnboxedDenseElements,
-                                 JSContext*, JSObject*, JSObject*, uint32_t, uint32_t, uint32_t);
-
-DenseElementResult
-js::CopyAnyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* dst, JSObject* src,
-                                       uint32_t dstStart, uint32_t srcStart, uint32_t length)
-{
-    CopyBoxedOrUnboxedDenseElementsFunctor functor(cx, dst, src, dstStart, srcStart, length);
-    return CallBoxedOrUnboxedSpecialization(functor, dst, src);
-}
-
-DefineBoxedOrUnboxedFunctor3(SetBoxedOrUnboxedInitializedLength,
-                             JSContext*, JSObject*, size_t);
-
-void
-js::SetAnyBoxedOrUnboxedInitializedLength(JSContext* cx, JSObject* obj, size_t initlen)
-{
-    SetBoxedOrUnboxedInitializedLengthFunctor functor(cx, obj, initlen);
-    JS_ALWAYS_TRUE(CallBoxedOrUnboxedSpecialization(functor, obj) == DenseElementResult::Success);
-}
-
-DefineBoxedOrUnboxedFunctor3(EnsureBoxedOrUnboxedDenseElements,
-                             JSContext*, JSObject*, size_t);
-
-DenseElementResult
-js::EnsureAnyBoxedOrUnboxedDenseElements(JSContext* cx, JSObject* obj, size_t initlen)
-{
-    EnsureBoxedOrUnboxedDenseElementsFunctor functor(cx, obj, initlen);
-    return CallBoxedOrUnboxedSpecialization(functor, obj);
-}
diff --git a/js/src/vm/UnboxedObject.h b/js/src/vm/UnboxedObject.h
deleted file mode 100644
index ecff8be5b..000000000
--- a/js/src/vm/UnboxedObject.h
+++ /dev/null
@@ -1,531 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
- * vim: set ts=8 sts=4 et sw=4 tw=99:
- * This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef vm_UnboxedObject_h
-#define vm_UnboxedObject_h
-
-#include "jsgc.h"
-#include "jsobj.h"
-
-#include "vm/Runtime.h"
-#include "vm/TypeInference.h"
-
-namespace js {
-
-// Memory required for an unboxed value of a given type. Returns zero for types
-// which can't be used for unboxed objects.
-static inline size_t
-UnboxedTypeSize(JSValueType type)
-{
-    switch (type) {
-      case JSVAL_TYPE_BOOLEAN: return 1;
-      case JSVAL_TYPE_INT32:   return 4;
-      case JSVAL_TYPE_DOUBLE:  return 8;
-      case JSVAL_TYPE_STRING:  return sizeof(void*);
-      case JSVAL_TYPE_OBJECT:  return sizeof(void*);
-      default:                 return 0;
-    }
-}
-
-static inline bool
-UnboxedTypeNeedsPreBarrier(JSValueType type)
-{
-    return type == JSVAL_TYPE_STRING || type == JSVAL_TYPE_OBJECT;
-}
-
-static inline bool
-UnboxedTypeNeedsPostBarrier(JSValueType type)
-{
-    return type == JSVAL_TYPE_OBJECT;
-}
-
-// Class tracking information specific to unboxed objects.
-class UnboxedLayout : public mozilla::LinkedListElement<UnboxedLayout>
-{
-  public:
-    struct Property {
-        PropertyName* name;
-        uint32_t offset;
-        JSValueType type;
-
-        Property()
-          : name(nullptr), offset(UINT32_MAX), type(JSVAL_TYPE_MAGIC)
-        {}
-    };
-
-    typedef Vector<Property, 0, SystemAllocPolicy> PropertyVector;
-
-  private:
-    // If objects in this group have ever been converted to native objects,
-    // these store the corresponding native group and initial shape for such
-    // objects. Type information for this object is reflected in nativeGroup.
-    GCPtrObjectGroup nativeGroup_;
-    GCPtrShape nativeShape_;
-
-    // Any script/pc which the associated group is created for.
-    GCPtrScript allocationScript_;
-    jsbytecode* allocationPc_;
-
-    // If nativeGroup is set and this object originally had a TypeNewScript or
-    // was keyed to an allocation site, this points to the group which replaced
-    // this one. This link is only needed to keep the replacement group from
-    // being GC'ed. If it were GC'ed and a new one regenerated later, that new
-    // group might have a different allocation kind from this group.
-    GCPtrObjectGroup replacementGroup_;
-
-    // The following members are only used for unboxed plain objects.
-
-    // All properties on objects with this layout, in enumeration order.
-    PropertyVector properties_;
-
-    // Byte size of the data for objects with this layout.
-    size_t size_;
-
-    // Any 'new' script information associated with this layout.
-    TypeNewScript* newScript_;
-
-    // List for use in tracing objects with this layout. This has the same
-    // structure as the trace list on a TypeDescr.
-    int32_t* traceList_;
-
-    // If this layout has been used to construct script or JSON constant
-    // objects, this code might be filled in to more quickly fill in objects
-    // from an array of values.
-    GCPtrJitCode constructorCode_;
-
-    // The following members are only used for unboxed arrays.
-
-    // The type of array elements.
-    JSValueType elementType_;
-
-  public:
-    UnboxedLayout()
-      : nativeGroup_(nullptr), nativeShape_(nullptr),
-        allocationScript_(nullptr), allocationPc_(nullptr), replacementGroup_(nullptr),
-        size_(0), newScript_(nullptr), traceList_(nullptr), constructorCode_(nullptr),
-        elementType_(JSVAL_TYPE_MAGIC)
-    {}
-
-    bool initProperties(const PropertyVector& properties, size_t size) {
-        size_ = size;
-        return properties_.appendAll(properties);
-    }
-
-    void initArray(JSValueType elementType) {
-        elementType_ = elementType;
-    }
-
-    ~UnboxedLayout() {
-        if (newScript_)
-            newScript_->clear();
-        js_delete(newScript_);
-        js_free(traceList_);
-
-        nativeGroup_.init(nullptr);
-        nativeShape_.init(nullptr);
-        replacementGroup_.init(nullptr);
-        constructorCode_.init(nullptr);
-    }
-
-    bool isArray() const {
-        return elementType_ != JSVAL_TYPE_MAGIC;
-    }
-
-    void detachFromCompartment();
-
-    const PropertyVector& properties() const {
-        return properties_;
-    }
-
-    TypeNewScript* newScript() const {
-        return newScript_;
-    }
-
-    void setNewScript(TypeNewScript* newScript, bool writeBarrier = true);
-
-    JSScript* allocationScript() const {
-        return allocationScript_;
-    }
-
-    jsbytecode* allocationPc() const {
-        return allocationPc_;
-    }
-
-    void setAllocationSite(JSScript* script, jsbytecode* pc) {
-        allocationScript_ = script;
-        allocationPc_ = pc;
-    }
-
-    const int32_t* traceList() const {
-        return traceList_;
-    }
-
-    void setTraceList(int32_t* traceList) {
-        traceList_ = traceList;
-    }
-
-    const Property* lookup(JSAtom* atom) const {
-        for (size_t i = 0; i < properties_.length(); i++) {
-            if (properties_[i].name == atom)
-                return &properties_[i];
-        }
-        return nullptr;
-    }
-
-    const Property* lookup(jsid id) const {
-        if (JSID_IS_STRING(id))
-            return lookup(JSID_TO_ATOM(id));
-        return nullptr;
-    }
-
-    size_t size() const {
-        return size_;
-    }
-
-    ObjectGroup* nativeGroup() const {
-        return nativeGroup_;
-    }
-
-    Shape* nativeShape() const {
-        return nativeShape_;
-    }
-
-    jit::JitCode* constructorCode() const {
-        return constructorCode_;
-    }
-
-    void setConstructorCode(jit::JitCode* code) {
-        constructorCode_ = code;
-    }
-
-    JSValueType elementType() const {
-        return elementType_;
-    }
-
-    inline gc::AllocKind getAllocKind() const;
-
-    void trace(JSTracer* trc);
-
-    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf);
-
-    static bool makeNativeGroup(JSContext* cx, ObjectGroup* group);
-    static bool makeConstructorCode(JSContext* cx, HandleObjectGroup group);
-};
-
-// Class for expando objects holding extra properties given to an unboxed plain
-// object. These objects behave identically to normal native plain objects, and
-// have a separate Class to distinguish them for memory usage reporting.
-class UnboxedExpandoObject : public NativeObject
-{
-  public:
-    static const Class class_;
-};
-
-// Class for a plain object using an unboxed representation. The physical
-// layout of these objects is identical to that of an InlineTypedObject, though
-// these objects use an UnboxedLayout instead of a TypeDescr to keep track of
-// how their properties are stored.
-class UnboxedPlainObject : public JSObject
-{
-    // Optional object which stores extra properties on this object. This is
-    // not automatically barriered to avoid problems if the object is converted
-    // to a native. See ensureExpando().
-    UnboxedExpandoObject* expando_;
-
-    // Start of the inline data, which immediately follows the group and extra properties.
-    uint8_t data_[1];
-
-  public:
-    static const Class class_;
-
-    static bool obj_lookupProperty(JSContext* cx, HandleObject obj,
-                                   HandleId id, MutableHandleObject objp,
-                                   MutableHandleShape propp);
-
-    static bool obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                   Handle<PropertyDescriptor> desc,
-                                   ObjectOpResult& result);
-
-    static bool obj_hasProperty(JSContext* cx, HandleObject obj, HandleId id, bool* foundp);
-
-    static bool obj_getProperty(JSContext* cx, HandleObject obj, HandleValue receiver,
-                                HandleId id, MutableHandleValue vp);
-
-    static bool obj_setProperty(JSContext* cx, HandleObject obj, HandleId id, HandleValue v,
-                                HandleValue receiver, ObjectOpResult& result);
-
-    static bool obj_getOwnPropertyDescriptor(JSContext* cx, HandleObject obj, HandleId id,
-                                             MutableHandle<PropertyDescriptor> desc);
-
-    static bool obj_deleteProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                   ObjectOpResult& result);
-
-    static bool obj_enumerate(JSContext* cx, HandleObject obj, AutoIdVector& properties,
-                              bool enumerableOnly);
-    static bool obj_watch(JSContext* cx, HandleObject obj, HandleId id, HandleObject callable);
-
-    inline const UnboxedLayout& layout() const;
-
-    const UnboxedLayout& layoutDontCheckGeneration() const {
-        return group()->unboxedLayoutDontCheckGeneration();
-    }
-
-    uint8_t* data() {
-        return &data_[0];
-    }
-
-    UnboxedExpandoObject* maybeExpando() const {
-        return expando_;
-    }
-
-    void initExpando() {
-        expando_ = nullptr;
-    }
-
-    // For use during GC.
-    JSObject** addressOfExpando() {
-        return reinterpret_cast<JSObject**>(&expando_);
-    }
-
-    bool containsUnboxedOrExpandoProperty(ExclusiveContext* cx, jsid id) const;
-
-    static UnboxedExpandoObject* ensureExpando(JSContext* cx, Handle<UnboxedPlainObject*> obj);
-
-    bool setValue(ExclusiveContext* cx, const UnboxedLayout::Property& property, const Value& v);
-    Value getValue(const UnboxedLayout::Property& property, bool maybeUninitialized = false);
-
-    static bool convertToNative(JSContext* cx, JSObject* obj);
-    static UnboxedPlainObject* create(ExclusiveContext* cx, HandleObjectGroup group,
-                                      NewObjectKind newKind);
-    static JSObject* createWithProperties(ExclusiveContext* cx, HandleObjectGroup group,
-                                          NewObjectKind newKind, IdValuePair* properties);
-
-    void fillAfterConvert(ExclusiveContext* cx,
-                          Handle<GCVector<Value>> values, size_t* valueCursor);
-
-    static void trace(JSTracer* trc, JSObject* object);
-
-    static size_t offsetOfExpando() {
-        return offsetof(UnboxedPlainObject, expando_);
-    }
-
-    static size_t offsetOfData() {
-        return offsetof(UnboxedPlainObject, data_[0]);
-    }
-};
-
-// Try to construct an UnboxedLayout for each of the preliminary objects,
-// provided they all match the template shape. If successful, converts the
-// preliminary objects and their group to the new unboxed representation.
-bool
-TryConvertToUnboxedLayout(ExclusiveContext* cx, AutoEnterAnalysis& enter, Shape* templateShape,
-                          ObjectGroup* group, PreliminaryObjectArray* objects);
-
-inline gc::AllocKind
-UnboxedLayout::getAllocKind() const
-{
-    MOZ_ASSERT(size());
-    return gc::GetGCObjectKindForBytes(UnboxedPlainObject::offsetOfData() + size());
-}
-
-// Class for an array object using an unboxed representation.
-class UnboxedArrayObject : public JSObject
-{
-    // Elements pointer for the object.
-    uint8_t* elements_;
-
-    // The nominal array length. This always fits in an int32_t.
-    uint32_t length_;
-
-    // Value indicating the allocated capacity and initialized length of the
-    // array. The top CapacityBits bits are an index into CapacityArray, which
-    // indicates the elements capacity. The low InitializedLengthBits store the
-    // initialized length of the array.
-    uint32_t capacityIndexAndInitializedLength_;
-
-    // If the elements are inline, they will point here.
-    uint8_t inlineElements_[1];
-
-  public:
-    static const uint32_t CapacityBits = 6;
-    static const uint32_t CapacityShift = 26;
-
-    static const uint32_t CapacityMask = uint32_t(-1) << CapacityShift;
-    static const uint32_t InitializedLengthMask = (1 << CapacityShift) - 1;
-
-    static const uint32_t MaximumCapacity = InitializedLengthMask;
-    static const uint32_t MinimumDynamicCapacity = 8;
-
-    static const uint32_t CapacityArray[];
-
-    // Capacity index which indicates the array's length is also its capacity.
-    static const uint32_t CapacityMatchesLengthIndex = 0;
-
-  private:
-    static inline uint32_t computeCapacity(uint32_t index, uint32_t length) {
-        if (index == CapacityMatchesLengthIndex)
-            return length;
-        return CapacityArray[index];
-    }
-
-    static uint32_t chooseCapacityIndex(uint32_t capacity, uint32_t length);
-    static uint32_t exactCapacityIndex(uint32_t capacity);
-
-  public:
-    static const Class class_;
-
-    static bool obj_lookupProperty(JSContext* cx, HandleObject obj,
-                                   HandleId id, MutableHandleObject objp,
-                                   MutableHandleShape propp);
-
-    static bool obj_defineProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                   Handle<PropertyDescriptor> desc,
-                                   ObjectOpResult& result);
-
-    static bool obj_hasProperty(JSContext* cx, HandleObject obj, HandleId id, bool* foundp);
-
-    static bool obj_getProperty(JSContext* cx, HandleObject obj, HandleValue receiver,
-                                HandleId id, MutableHandleValue vp);
-
-    static bool obj_setProperty(JSContext* cx, HandleObject obj, HandleId id, HandleValue v,
-                                HandleValue receiver, ObjectOpResult& result);
-
-    static bool obj_getOwnPropertyDescriptor(JSContext* cx, HandleObject obj, HandleId id,
-                                             MutableHandle<PropertyDescriptor> desc);
-
-    static bool obj_deleteProperty(JSContext* cx, HandleObject obj, HandleId id,
-                                   ObjectOpResult& result);
-
-    static bool obj_enumerate(JSContext* cx, HandleObject obj, AutoIdVector& properties,
-                              bool enumerableOnly);
-    static bool obj_watch(JSContext* cx, HandleObject obj, HandleId id, HandleObject callable);
-
-    inline const UnboxedLayout& layout() const;
-
-    const UnboxedLayout& layoutDontCheckGeneration() const {
-        return group()->unboxedLayoutDontCheckGeneration();
-    }
-
-    JSValueType elementType() const {
-        return layoutDontCheckGeneration().elementType();
-    }
-
-    uint32_t elementSize() const {
-        return UnboxedTypeSize(elementType());
-    }
-
-    static bool convertToNative(JSContext* cx, JSObject* obj);
-    static UnboxedArrayObject* create(ExclusiveContext* cx, HandleObjectGroup group,
-                                      uint32_t length, NewObjectKind newKind,
-                                      uint32_t maxLength = MaximumCapacity);
-
-    static bool convertToNativeWithGroup(ExclusiveContext* cx, JSObject* obj,
-                                         ObjectGroup* group, Shape* shape);
-    bool convertInt32ToDouble(ExclusiveContext* cx, ObjectGroup* group);
-
-    void fillAfterConvert(ExclusiveContext* cx,
-                          Handle<GCVector<Value>> values, size_t* valueCursor);
-
-    static void trace(JSTracer* trc, JSObject* object);
-    static void objectMoved(JSObject* obj, const JSObject* old);
-    static void finalize(FreeOp* fop, JSObject* obj);
-
-    static size_t objectMovedDuringMinorGC(JSTracer* trc, JSObject* dst, JSObject* src,
-                                           gc::AllocKind allocKind);
-
-    uint8_t* elements() {
-        return elements_;
-    }
-
-    bool hasInlineElements() const {
-        return elements_ == &inlineElements_[0];
-    }
-
-    uint32_t length() const {
-        return length_;
-    }
-
-    uint32_t initializedLength() const {
-        return capacityIndexAndInitializedLength_ & InitializedLengthMask;
-    }
-
-    uint32_t capacityIndex() const {
-        return (capacityIndexAndInitializedLength_ & CapacityMask) >> CapacityShift;
-    }
-
-    uint32_t capacity() const {
-        return computeCapacity(capacityIndex(), length());
-    }
-
-    bool containsProperty(ExclusiveContext* cx, jsid id);
-
-    bool setElement(ExclusiveContext* cx, size_t index, const Value& v);
-    bool initElement(ExclusiveContext* cx, size_t index, const Value& v);
-    void initElementNoTypeChange(size_t index, const Value& v);
-    Value getElement(size_t index);
-
-    template <JSValueType Type> inline bool setElementSpecific(ExclusiveContext* cx, size_t index,
-                                                               const Value& v);
-    template <JSValueType Type> inline void setElementNoTypeChangeSpecific(size_t index, const Value& v);
-    template <JSValueType Type> inline bool initElementSpecific(ExclusiveContext* cx, size_t index,
-                                                                const Value& v);
-    template <JSValueType Type> inline void initElementNoTypeChangeSpecific(size_t index, const Value& v);
-    template <JSValueType Type> inline Value getElementSpecific(size_t index);
-    template <JSValueType Type> inline void triggerPreBarrier(size_t index);
-
-    bool growElements(ExclusiveContext* cx, size_t cap);
-    void shrinkElements(ExclusiveContext* cx, size_t cap);
-
-    static uint32_t offsetOfElements() {
-        return offsetof(UnboxedArrayObject, elements_);
-    }
-    static uint32_t offsetOfLength() {
-        return offsetof(UnboxedArrayObject, length_);
-    }
-    static uint32_t offsetOfCapacityIndexAndInitializedLength() {
-        return offsetof(UnboxedArrayObject, capacityIndexAndInitializedLength_);
-    }
-    static uint32_t offsetOfInlineElements() {
-        return offsetof(UnboxedArrayObject, inlineElements_);
-    }
-
-    void setLengthInt32(uint32_t length) {
-        MOZ_ASSERT(length <= INT32_MAX);
-        length_ = length;
-    }
-
-    inline void setLength(ExclusiveContext* cx, uint32_t len);
-    inline void setInitializedLength(uint32_t initlen);
-
-    inline void setInitializedLengthNoBarrier(uint32_t initlen) {
-        MOZ_ASSERT(initlen <= InitializedLengthMask);
-        capacityIndexAndInitializedLength_ =
-            (capacityIndexAndInitializedLength_ & CapacityMask) | initlen;
-    }
-
-  private:
-    void setInlineElements() {
-        elements_ = &inlineElements_[0];
-    }
-
-    void setCapacityIndex(uint32_t index) {
-        MOZ_ASSERT(index <= (CapacityMask >> CapacityShift));
-        capacityIndexAndInitializedLength_ =
-            (index << CapacityShift) | initializedLength();
-    }
-};
-
-} // namespace js
-
-namespace JS {
-
-template <>
-struct DeletePolicy<js::UnboxedLayout> : public js::GCManagedDeletePolicy<js::UnboxedLayout>
-{};
-
-} /* namespace JS */
-
-#endif /* vm_UnboxedObject_h */