Make x64 to use the RecordWrite stub. This is a step towards getting

src/ia32/code-stubs-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6218 matching lines @@
   __ ret(2 * kPointerSize);
 }
 
 
 // Takes the input in 3 registers: address_ value_ and object_.  A pointer to
 // the value has just been written into the object, now this stub makes sure
 // we keep the GC informed.  The word in the object where the value has been
 // written is in the address register.
 void RecordWriteStub::Generate(MacroAssembler* masm) {
   Label skip_non_incremental_part;
+
+  // The first instruction is generated as a label so as to get the offset
+  // fixed up correctly by the bind(Label*) call.  We patch it back and forth
+  // between a 2-byte compare instruction (a nop in this position) and the real
+  // branch when we start and stop incremental heap marking.
   __ jmp(&skip_non_incremental_part, Label::kNear);
-  if (!HEAP->incremental_marking()->IsMarking()) {
-    ASSERT(masm->get_opcode(-2) == kSkipNonIncrementalPartInstruction);
-    masm->set_opcode(-2, kTwoByteNopInstruction);
+  if (!masm->isolate()->heap()->incremental_marking()->IsMarking()) {
+    ASSERT(masm->byte_at(masm->pc_offset() - 2) ==
+           kSkipNonIncrementalPartInstruction);
+    masm->set_byte_at(masm->pc_offset() - 2, kTwoByteNopInstruction);
   }
 
   if (remembered_set_action_ == EMIT_REMEMBERED_SET) {
     __ RememberedSetHelper(
         address_, value_, save_fp_regs_mode_, MacroAssembler::kReturnAtEnd);
   } else {
     __ ret(0);
   }
 
   __ bind(&skip_non_incremental_part);
@@ skipping 109 matching lines @@
 
   // Fall through when we need to inform the incremental marker.
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32