Supported folding of constant size allocation followed by dynamic size allocation.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 272c6bdaf044a8906b201348da851e49ac80a815..1800f7310d7b0e70f0ee66c84c7f03c9a5ccb9bd 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -1237,6 +1237,8 @@ class HInstruction : public HValue {
     position_.set_operand_position(index, pos);
   }
 
+  bool Dominates(HInstruction* other);
+
   bool CanTruncateToInt32() const { return CheckFlag(kTruncatingToInt32); }
 
   virtual LInstruction* CompileToLithium(LChunkBuilder* builder) = 0;
@@ -5450,6 +5452,9 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
   HValue* context() { return OperandAt(0); }
   HValue* size() { return OperandAt(1); }
 
+  HAllocate* wired_allocate() { return wired_allocate_; }
+  void set_wired_allocate(HAllocate* alloc) { wired_allocate_ = alloc; }
+
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     if (index == 0) {
       return Representation::Tagged();
@@ -5517,6 +5522,7 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
             InstanceType instance_type)
       : HTemplateInstruction<2>(type),
         dominating_allocate_(NULL),
+        wired_allocate_(NULL),
         filler_free_space_size_(NULL),
         clear_next_map_word_(false) {
     SetOperandAt(0, context);
@@ -5566,6 +5572,9 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
   Flags flags_;
   Handle<Map> known_initial_map_;
   HAllocate* dominating_allocate_;
+  // JSArray allocation will contain pointer to FixedArray allocation here.
+  // Allocation folding will treat wired allocations differently.
+  HAllocate* wired_allocate_;
   HStoreNamedField* filler_free_space_size_;
   bool clear_next_map_word_;
 };