[turbofan] Initial version of allocation folding and write barrier elimination.

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index d0664a1ff1d8a4cd15cd46532226fe7c66a3cb6b..707da746c19da72bc7923afd473725eb701e7997 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -94,7 +94,6 @@ namespace internal {
   V(LoadIC)                                 \
   /* TurboFanCodeStubs */                   \
   V(AllocateHeapNumber)                     \
-  V(AllocateMutableHeapNumber)              \
   V(AllocateFloat32x4)                      \
   V(AllocateInt32x4)                        \
   V(AllocateUint32x4)                       \
@@ -2743,18 +2742,6 @@ class AllocateHeapNumberStub : public TurboFanCodeStub {
   DEFINE_CODE_STUB(AllocateHeapNumber, TurboFanCodeStub);
 };
 
-class AllocateMutableHeapNumberStub : public TurboFanCodeStub {
- public:
-  explicit AllocateMutableHeapNumberStub(Isolate* isolate)
-      : TurboFanCodeStub(isolate) {}
-
-  void InitializeDescriptor(CodeStubDescriptor* descriptor) override;
-  void GenerateAssembly(CodeStubAssembler* assembler) const override;
-
-  DEFINE_CALL_INTERFACE_DESCRIPTOR(AllocateMutableHeapNumber);
-  DEFINE_CODE_STUB(AllocateMutableHeapNumber, TurboFanCodeStub);
-};
-
 #define SIMD128_ALLOC_STUB(TYPE, Type, type, lane_count, lane_type)     \
   class Allocate##Type##Stub : public TurboFanCodeStub {                \
    public:                                                              \