Merge branch 'master' into FrameProperties

23 files changed, 54 insertions, 1426 deletions

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;