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

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 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/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 2597 matching lines @@
     __ movp(temp, FieldOperand(input, HeapObject::kMapOffset));
     __ movzxbl(temp2, FieldOperand(temp, Map::kInstanceTypeOffset));
     __ subp(temp2, Immediate(FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
     __ cmpp(temp2, Immediate(LAST_NONCALLABLE_SPEC_OBJECT_TYPE -
                              FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
     __ j(above, is_false);
   }
 
   // Now we are in the FIRST-LAST_NONCALLABLE_SPEC_OBJECT_TYPE range.
   // Check if the constructor in the map is a function.
-  __ movp(temp, FieldOperand(temp, Map::kConstructorOffset));
+  __ GetMapConstructor(temp, temp, kScratchRegister);
 
   // Objects with a non-function constructor have class 'Object'.
-  __ CmpObjectType(temp, JS_FUNCTION_TYPE, kScratchRegister);
+  __ CmpInstanceType(kScratchRegister, JS_FUNCTION_TYPE);
   if (String::Equals(class_name, isolate()->factory()->Object_string())) {
     __ j(not_equal, is_true);
   } else {
     __ j(not_equal, is_false);
   }
 
   // temp now contains the constructor function. Grab the
   // instance class name from there.
   __ movp(temp, FieldOperand(temp, JSFunction::kSharedFunctionInfoOffset));
   __ movp(temp, FieldOperand(temp,
@@ skipping 3304 matching lines @@
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64