Move Maps' back pointers from "transitions" to "constructor" field

src/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
@@ skipping 3648 matching lines @@
   __ j(equal, &function);
 
   __ CmpInstanceType(rax, LAST_SPEC_OBJECT_TYPE);
   STATIC_ASSERT(LAST_NONCALLABLE_SPEC_OBJECT_TYPE ==
                 LAST_SPEC_OBJECT_TYPE - 1);
   __ j(equal, &function);
   // Assume that there is no larger type.
   STATIC_ASSERT(LAST_NONCALLABLE_SPEC_OBJECT_TYPE == LAST_TYPE - 1);
 
   // Check if the constructor in the map is a JS function.
-  __ movp(rax, FieldOperand(rax, Map::kConstructorOffset));
-  __ CmpObjectType(rax, JS_FUNCTION_TYPE, rbx);
+  __ GetMapConstructor(rax, rax, rbx);
+  __ CmpInstanceType(rbx, JS_FUNCTION_TYPE);
   __ j(not_equal, &non_function_constructor);
 
   // rax now contains the constructor function. Grab the
   // instance class name from there.
   __ movp(rax, FieldOperand(rax, JSFunction::kSharedFunctionInfoOffset));
   __ movp(rax, FieldOperand(rax, SharedFunctionInfo::kInstanceClassNameOffset));
   __ jmp(&done);
 
   // Functions have class 'Function'.
   __ bind(&function);
@@ skipping 1706 matching lines @@
   DCHECK_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64