Merge branch 'master' into FrameProperties

49 files changed, 76 insertions, 3419 deletions

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/BaselineCacheIR.cpp b/js/src/jit/BaselineCacheIR.cpp
index 7fb586811..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:
@@ -815,36 +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());
@@ -871,26 +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;
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index 64cdf01a6..2f20ffa4f 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;
 
@@ -289,7 +289,7 @@ DoTypeUpdateFallback(JSContext* cx, BaselineFrame* frame, ICUpdatedStub* stub, H
       case ICStub::SetProp_Native:
       case ICStub::SetProp_NativeAdd:
       case ICStub::SetProp_Unboxed: {
-        MOZ_ASSERT(obj->isNative() || obj->is<UnboxedPlainObject>());
+        MOZ_ASSERT(obj->isNative());
         jsbytecode* pc = stub->getChainFallback()->icEntry()->pc(script);
         if (*pc == JSOP_SETALIASEDVAR || *pc == JSOP_INITALIASEDLEXICAL)
             id = NameToId(EnvironmentCoordinateName(cx->caches.envCoordinateNameCache, script, pc));
@@ -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;
 
@@ -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,
@@ -1862,14 +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()) {
@@ -1920,13 +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);
@@ -2673,18 +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)
 {
@@ -4131,18 +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;
@@ -4293,40 +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)
@@ -4409,12 +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
@@ -4487,15 +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;
@@ -4578,20 +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
@@ -4630,13 +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();
@@ -4773,31 +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
@@ -4829,70 +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);
@@ -5652,7 +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;
         }
 
diff --git a/js/src/jit/BaselineIC.h b/js/src/jit/BaselineIC.h
index 901fca9cc..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 {
@@ -1823,8 +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);
@@ -1929,7 +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);
     }
 
@@ -1954,10 +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_);
diff --git a/js/src/jit/BaselineInspector.cpp b/js/src/jit/BaselineInspector.cpp
index bcb527516..3b852debf 100644
--- a/js/src/jit/BaselineInspector.cpp
+++ b/js/src/jit/BaselineInspector.cpp
@@ -104,19 +104,11 @@ AddReceiver(const ReceiverGuard& 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());
@@ -125,14 +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);
@@ -141,29 +125,6 @@ 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)
 {
@@ -182,8 +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;
@@ -191,8 +151,6 @@ 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;
diff --git a/js/src/jit/CacheIR.cpp b/js/src/jit/CacheIR.cpp
index 6822a70af..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<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_);
diff --git a/js/src/jit/CacheIR.h b/js/src/jit/CacheIR.h
index 4fd8575f0..ae55cfebb 100644
--- a/js/src/jit/CacheIR.h
+++ b/js/src/jit/CacheIR.h
@@ -87,13 +87,10 @@ class ObjOperandId : public OperandId
     _(GuardClass)                         \
     _(GuardSpecificObject)                \
     _(GuardNoDetachedTypedObjects)        \
-    _(GuardNoUnboxedExpando)              \
-    _(GuardAndLoadUnboxedExpando)         \
     _(LoadObject)                         \
     _(LoadProto)                          \
     _(LoadFixedSlotResult)                \
     _(LoadDynamicSlotResult)              \
-    _(LoadUnboxedPropertyResult)          \
     _(LoadTypedObjectResult)              \
     _(LoadInt32ArrayLengthResult)         \
     _(LoadArgumentsObjectLengthResult)    \
@@ -274,15 +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_++);
@@ -308,11 +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);
@@ -406,9 +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 e0b8a7f28..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"
@@ -3027,7 +3028,7 @@ 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);
@@ -3049,13 +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()) {
@@ -3121,12 +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()) {
@@ -3292,7 +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());
@@ -8382,11 +8379,6 @@ CodeGenerator::visitStoreUnboxedPointer(LStoreUnboxedPointer* lir)
     }
 }
 
-typedef bool (*ConvertUnboxedObjectToNativeFn)(JSContext*, JSObject*);
-static const VMFunction ConvertUnboxedPlainObjectToNativeInfo =
-    FunctionInfo<ConvertUnboxedObjectToNativeFn>(UnboxedPlainObject::convertToNative,
-                                                 "UnboxedPlainObject::convertToNative");
-
 typedef bool (*ArrayPopShiftFn)(JSContext*, HandleObject, MutableHandleValue);
 static const VMFunction ArrayPopDenseInfo =
     FunctionInfo<ArrayPopShiftFn>(jit::ArrayPopDense, "ArrayPopDense");
@@ -8679,11 +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);
 
@@ -8695,12 +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);
     }
 
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index fc864a197..a54a58add 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -10925,63 +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;
-        }
-
-        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()
 {
@@ -11948,72 +11891,6 @@ 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;
-}
-
 MDefinition*
 IonBuilder::addShapeGuardsForGetterSetter(MDefinition* obj, JSObject* holder, Shape* holderShape,
                 const BaselineInspector::ReceiverVector& receivers,
@@ -12835,66 +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::setPropTryInlineAccess(bool* emitted, MDefinition* obj,
                                    PropertyName* name, MDefinition* value,
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index 1b97c4743..dd40b4bd6 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -1048,19 +1048,6 @@ class IonBuilder
     ResultWithOOM<bool> testNotDefinedProperty(MDefinition* obj, jsid id);
 
     uint32_t getDefiniteSlot(TemporaryTypeSet* types, PropertyName* name, uint32_t* pnfixed);
-    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 81cf9d9bb..9901bdd07 100644
--- a/js/src/jit/IonCaches.cpp
+++ b/js/src/jit/IonCaches.cpp
@@ -31,7 +31,6 @@
 #include "jit/shared/Lowering-shared-inl.h"
 #include "vm/Interpreter-inl.h"
 #include "vm/Shape-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -620,26 +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<TypedObject>()) {
+    if (obj->is<TypedObject>()) {
         attacher.branchNextStubOrLabel(masm, Assembler::NotEqual,
                                        Address(object, JSObject::offsetOfGroup()),
                                        ImmGCPtr(obj->group()), failure);
@@ -756,7 +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());
 
@@ -775,7 +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()) {
@@ -836,10 +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;
     }
@@ -867,30 +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,
@@ -1498,67 +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::tryAttachTypedArrayLength(JSContext* cx, HandleScript outerScript, IonScript* ion,
                                          HandleObject obj, HandleId id, bool* emitted)
 {
@@ -2127,12 +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 && !tryAttachTypedArrayLength(cx, outerScript, ion, obj, id, emitted))
             return false;
     }
@@ -2311,12 +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()));
 
@@ -2954,23 +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.
@@ -2991,9 +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());
@@ -3004,12 +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);
@@ -3026,27 +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())
@@ -3054,8 +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.
@@ -3298,141 +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)
@@ -3514,26 +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)
@@ -3558,12 +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()) {
@@ -3615,16 +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;
 }
 
@@ -3646,11 +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);
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/MCallOptimize.cpp b/js/src/jit/MCallOptimize.cpp
index fed5aefe5..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;
diff --git a/js/src/jit/MIR.cpp b/js/src/jit/MIR.cpp
index 190b40bb2..fa9cc3019 100644
--- a/js/src/jit/MIR.cpp
+++ b/js/src/jit/MIR.cpp
@@ -4817,15 +4817,14 @@ MCreateThisWithTemplate::canRecoverOnBailout() const
 
 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);
@@ -4836,8 +4835,6 @@ MObjectState::MObjectState(JSObject *templateObject, OperandIndexMap* operandInd
     NativeObject* nativeObject = &templateObject->as<NativeObject>();
     numSlots_ = nativeObject->slotSpan();
     numFixedSlots_ = nativeObject->numFixedSlots();
-
-    operandIndex_ = operandIndex;
 }
 
 JSObject*
@@ -4897,7 +4894,7 @@ MObjectState::New(TempAllocator& alloc, MDefinition* obj)
     JSObject* templateObject = templateObjectOf(obj);
     MOZ_ASSERT(templateObject, "Unexpected object creation.");
 
-    MObjectState* res = new(alloc) MObjectState(templateObject, nullptr);
+    MObjectState* res = new(alloc) MObjectState(templateObject);
     if (!res || !res->init(alloc, obj))
         return nullptr;
     return res;
diff --git a/js/src/jit/MIR.h b/js/src/jit/MIR.h
index 6526e0931..9076339f1 100644
--- a/js/src/jit/MIR.h
+++ b/js/src/jit/MIR.h
@@ -375,7 +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
-                                    // 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
@@ -3758,14 +3758,9 @@ class MObjectState
 {
   private:
     uint32_t numSlots_;
-    uint32_t numFixedSlots_;        // valid if isUnboxed() == false.
-    OperandIndexMap* operandIndex_; // valid if isUnboxed() == true.
+    uint32_t numFixedSlots_;
 
-    bool isUnboxed() const {
-        return operandIndex_ != nullptr;
-    }
-
-    MObjectState(JSObject *templateObject, OperandIndexMap* operandIndex);
+    MObjectState(JSObject *templateObject);
     explicit MObjectState(MObjectState* state);
 
     MOZ_MUST_USE bool init(TempAllocator& alloc, MDefinition* obj);
@@ -3790,7 +3785,6 @@ class MObjectState
     MOZ_MUST_USE bool initFromTemplateObject(TempAllocator& alloc, MDefinition* undefinedVal);
 
     size_t numFixedSlots() const {
-        MOZ_ASSERT(!isUnboxed());
         return numFixedSlots_;
     }
     size_t numSlots() const {
@@ -3826,18 +3820,6 @@ 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;
diff --git a/js/src/jit/MacroAssembler.cpp b/js/src/jit/MacroAssembler.cpp
index e50f68722..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);
@@ -468,243 +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);
-
 // Inlined version of gc::CheckAllocatorState that checks the bare essentials
 // and bails for anything that cannot be handled with our jit allocators.
 void
@@ -1252,10 +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 {
         MOZ_CRASH("Unknown object");
     }
@@ -1277,29 +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 6ee989463..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;
 
@@ -1626,17 +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.
-    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);
-
     Register extractString(const Address& address, Register scratch) {
         return extractObject(address, scratch);
     }
@@ -1713,8 +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 b42634d43..7d72795a0 100644
--- a/js/src/jit/OptimizationTracking.cpp
+++ b/js/src/jit/OptimizationTracking.cpp
@@ -15,11 +15,9 @@
 #include "jit/JitcodeMap.h"
 #include "jit/JitSpewer.h"
 #include "js/TrackedOptimizationInfo.h"
-#include "vm/UnboxedObject.h"
 
 #include "vm/ObjectGroup-inl.h"
 #include "vm/TypeInference-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -846,8 +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 8fe6ee3fb..793b631df 100644
--- a/js/src/jit/Recover.cpp
+++ b/js/src/jit/Recover.cpp
@@ -30,7 +30,6 @@
 
 #include "vm/Interpreter-inl.h"
 #include "vm/NativeObject-inl.h"
-#include "vm/UnboxedObject-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -1540,37 +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 be9ceee2e..97ba52349 100644
--- a/js/src/jit/ScalarReplacement.cpp
+++ b/js/src/jit/ScalarReplacement.cpp
@@ -285,10 +285,6 @@ class ObjectMemoryView : public MDefinitionVisitorDefaultNoop
     void visitGuardShape(MGuardShape* ins);
     void visitFunctionEnvironment(MFunctionEnvironment* ins);
     void visitLambda(MLambda* 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";
@@ -630,35 +626,6 @@ ObjectMemoryView::visitLambda(MLambda* ins)
     ins->setIncompleteObject();
 }
 
-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);
-}
-
 static bool
 IndexOf(MDefinition* ins, int32_t* res)
 {
diff --git a/js/src/jit/SharedIC.cpp b/js/src/jit/SharedIC.cpp
index 313957462..05a95824f 100644
--- a/js/src/jit/SharedIC.cpp
+++ b/js/src/jit/SharedIC.cpp
@@ -2244,8 +2244,7 @@ IsCacheableProtoChain(JSObject* obj, JSObject* holder, bool isDOMProxy)
     if (!isDOMProxy && !obj->isNative()) {
         if (obj == holder)
             return false;
-        if (!obj->is<UnboxedPlainObject>() &&
-            !obj->is<TypedObject>())
+        if (!obj->is<TypedObject>())
         {
             return false;
         }
@@ -2573,9 +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<TypedObject>()) {
             if (curObj->as<TypedObject>().typeDescr().hasProperty(cx->names(), NameToId(name)))
                 return false;
@@ -2840,34 +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);
     }
 }
 
@@ -4251,8 +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 297357b1e..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;
diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index 5854fda4c..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;
diff --git a/js/src/jscompartment.cpp b/js/src/jscompartment.cpp
index a48bb0ffe..6024a1768 100644
--- a/js/src/jscompartment.cpp
+++ b/js/src/jscompartment.cpp
@@ -112,13 +112,6 @@ JSCompartment::~JSCompartment()
     js_delete(nonSyntacticLexicalEnvironments_),
     js_free(enumerators);
 
-#ifdef DEBUG
-    // Avoid assertion destroying the unboxed layouts list if the embedding
-    // leaked GC things.
-    if (!rt->gc.shutdownCollectedEverything())
-        unboxedLayouts.clear();
-#endif
-
     runtime_->numCompartments--;
 }
 
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 1fd9d1d28..5baba0beb 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -269,7 +269,7 @@ 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>())
         *cls = ESClass::Array;
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index deaa1d53e..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"
@@ -54,7 +55,6 @@
 #include "vm/RegExpStaticsObject.h"
 #include "vm/Shape.h"
 #include "vm/TypedArrayCommon.h"
-#include "vm/UnboxedObject-inl.h"
 
 #include "jsatominlines.h"
 #include "jsboolinlines.h"
diff --git a/js/src/jsobjinlines.h b/js/src/jsobjinlines.h
index 26f9eacce..b1d817bca 100644
--- a/js/src/jsobjinlines.h
+++ b/js/src/jsobjinlines.h
@@ -32,19 +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);
-    return true;
-}
-
-} // namespace js
-
 inline js::Shape*
 JSObject::maybeShape() const
 {
@@ -57,8 +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/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 29cbd9762..617b5e902 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -7536,7 +7536,6 @@ SetWorkerContextOptions(JSContext* cx)
                              .setWasm(enableWasm)
                              .setWasmAlwaysBaseline(enableWasmAlwaysBaseline)
                              .setNativeRegExp(enableNativeRegExp)
-                             .setUnboxedArrays(enableUnboxedArrays)
                              .setArrayProtoValues(enableArrayProtoValues);
     cx->setOffthreadIonCompilationEnabled(offthreadCompilation);
     cx->profilingScripts = enableCodeCoverage || enableDisassemblyDumps;
@@ -7706,7 +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', "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/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 74a1ef3e9..0f83c3435 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -4970,11 +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;
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 da4f873a6..d9d8b8aec 100644
--- a/js/src/vm/NativeObject.h
+++ b/js/src/vm/NativeObject.h
@@ -470,11 +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.
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 63ac33eea..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;
     }
@@ -971,46 +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;
@@ -1234,12 +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.
diff --git a/js/src/vm/ObjectGroup.h b/js/src/vm/ObjectGroup.h
index 553cb8366..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:
@@ -511,8 +463,8 @@ class ObjectGroup : public gc::TenuredCell
                                        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/ReceiverGuard.cpp b/js/src/vm/ReceiverGuard.cpp
index e37bf8ee5..e95e8a208 100644
--- a/js/src/vm/ReceiverGuard.cpp
+++ b/js/src/vm/ReceiverGuard.cpp
@@ -15,11 +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<TypedObject>()) {
+        if (obj->is<TypedObject>()) {
             group = obj->group();
         } else {
             shape = obj->maybeShape();
@@ -32,9 +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 (IsTypedObjectClass(clasp)) {
+        if (IsTypedObjectClass(clasp)) {
             this->shape = nullptr;
         } else {
             this->group = nullptr;
@@ -45,10 +39,6 @@ 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<TypedObject>()) {
         // Only the group needs to be guarded for typed objects.
         return 2;
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 0551e2c58..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
@@ -2505,8 +2474,6 @@ TemporaryTypeSet::propertyNeedsBarrier(CompilerConstraintList* constraints, jsid
 bool
 js::ClassCanHaveExtraProperties(const Class* clasp)
 {
-    if (clasp == &UnboxedPlainObject::class_)
-        return false;
     return clasp->getResolve()
         || clasp->getOpsLookupProperty()
         || clasp->getOpsGetProperty()
@@ -2805,15 +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
@@ -2885,12 +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
@@ -2923,23 +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
@@ -2949,7 +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()) {
@@ -2968,10 +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
@@ -2982,7 +2914,7 @@ ObjectGroup::maybeClearNewScriptOnOOM()
     if (!isMarked())
         return;
 
-    TypeNewScript* newScript = anyNewScript();
+    TypeNewScript* newScript = this->newScript();
     if (!newScript)
         return;
 
@@ -2997,7 +2929,7 @@ ObjectGroup::maybeClearNewScriptOnOOM()
 void
 ObjectGroup::clearNewScript(ExclusiveContext* cx, ObjectGroup* replacement /* = nullptr*/)
 {
-    TypeNewScript* newScript = anyNewScript();
+    TypeNewScript* newScript = this->newScript();
     if (!newScript)
         return;
 
@@ -3451,22 +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;
         }
     }
@@ -3566,16 +3482,11 @@ PreliminaryObjectArrayWithTemplate::maybeAnalyze(ExclusiveContext* cx, ObjectGro
         }
     }
 
-    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());
 }
 
 /////////////////////////////////////////////////////////////////////
@@ -3589,7 +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.
@@ -3852,27 +3762,6 @@ TypeNewScript::maybeAnalyze(JSContext* cx, ObjectGroup* group, bool* regenerate,
     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
@@ -3968,12 +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>());
 
@@ -4167,12 +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;
@@ -4256,21 +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/UnboxedObject-inl.h b/js/src/vm/UnboxedObject-inl.h
deleted file mode 100644
index c1468a5b1..000000000
--- a/js/src/vm/UnboxedObject-inl.h
+++ /dev/null
@@ -1,177 +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();
-}
-
-} // 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 806a9db81..000000000
--- a/js/src/vm/UnboxedObject.cpp
+++ /dev/null
@@ -1,956 +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);
-
-    // 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()) {
-        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, &PlainObject::class_, proto);
-        if (!replacementGroup)
-            return false;
-
-        PlainObject* templateObject = &script->getObject(pc)->as<PlainObject>();
-        replacementGroup->addDefiniteProperties(cx, templateObject->lastProperty());
-
-        cx->compartment()->objectGroups.replaceAllocationSiteGroup(script, pc, JSProto_Object,
-                                                                   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 = gc::GetGCKindSlots(layout.getAllocKind());
-
-    RootedShape shape(cx, EmptyShape::getInitialShape(cx, &PlainObject::class_, proto, nfixed, 0));
-    if (!shape)
-        return false;
-
-    // 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, &PlainObject::class_, 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.
-        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
-};
-
-/////////////////////////////////////////////////////////////////////
-// API
-/////////////////////////////////////////////////////////////////////
-
-static inline Value
-NextValue(Handle<GCVector<Value>> values, size_t* valueCursor)
-{
-    return values[(*valueCursor)++];
-}
-
-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)));
-}
diff --git a/js/src/vm/UnboxedObject.h b/js/src/vm/UnboxedObject.h
deleted file mode 100644
index ba66434bc..000000000
--- a/js/src/vm/UnboxedObject.h
+++ /dev/null
@@ -1,319 +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_;
-
-  public:
-    UnboxedLayout()
-      : nativeGroup_(nullptr), nativeShape_(nullptr),
-        allocationScript_(nullptr), allocationPc_(nullptr), replacementGroup_(nullptr),
-        size_(0), newScript_(nullptr), traceList_(nullptr), constructorCode_(nullptr)
-    {}
-
-    bool initProperties(const PropertyVector& properties, size_t size) {
-        size_ = size;
-        return properties_.appendAll(properties);
-    }
-
-    ~UnboxedLayout() {
-        if (newScript_)
-            newScript_->clear();
-        js_delete(newScript_);
-        js_free(traceList_);
-
-        nativeGroup_.init(nullptr);
-        nativeShape_.init(nullptr);
-        replacementGroup_.init(nullptr);
-        constructorCode_.init(nullptr);
-    }
-
-    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;
-    }
-
-    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]);
-    }
-};
-
-inline gc::AllocKind
-UnboxedLayout::getAllocKind() const
-{
-    MOZ_ASSERT(size());
-    return gc::GetGCObjectKindForBytes(UnboxedPlainObject::offsetOfData() + size());
-}
-
-} // namespace js
-
-namespace JS {
-
-template <>
-struct DeletePolicy<js::UnboxedLayout> : public js::GCManagedDeletePolicy<js::UnboxedLayout>
-{};
-
-} /* namespace JS */
-
-#endif /* vm_UnboxedObject_h */