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

src/arm/lithium-codegen-arm.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"
 
 #include "src/arm/lithium-codegen-arm.h"
 #include "src/arm/lithium-gap-resolver-arm.h"
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 2712 matching lines @@
     __ ldr(temp, FieldMemOperand(input, HeapObject::kMapOffset));
     __ ldrb(temp2, FieldMemOperand(temp, Map::kInstanceTypeOffset));
     __ sub(temp2, temp2, Operand(FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
     __ cmp(temp2, Operand(LAST_NONCALLABLE_SPEC_OBJECT_TYPE -
                           FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
     __ b(gt, is_false);
   }
 
   // Now we are in the FIRST-LAST_NONCALLABLE_SPEC_OBJECT_TYPE range.
   // Check if the constructor in the map is a function.
-  __ ldr(temp, FieldMemOperand(temp, Map::kConstructorOffset));
+  Register instance_type = ip;
+  __ GetMapConstructor(temp, temp, temp2, instance_type);
 
   // Objects with a non-function constructor have class 'Object'.
-  __ CompareObjectType(temp, temp2, temp2, JS_FUNCTION_TYPE);
+  __ cmp(instance_type, Operand(JS_FUNCTION_TYPE));
   if (class_name->IsOneByteEqualTo(STATIC_CHAR_VECTOR("Object"))) {
     __ b(ne, is_true);
   } else {
     __ b(ne, is_false);
   }
 
   // temp now contains the constructor function. Grab the
   // instance class name from there.
   __ ldr(temp, FieldMemOperand(temp, JSFunction::kSharedFunctionInfoOffset));
   __ ldr(temp, FieldMemOperand(temp,
@@ skipping 3235 matching lines @@
   __ Push(scope_info);
   __ push(ToRegister(instr->function()));
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal