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

src/arm/macro-assembler-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 <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_ARM
 
@@ skipping 2274 matching lines @@
 }
 
 
 void MacroAssembler::LoadWeakValue(Register value, Handle<WeakCell> cell,
                                    Label* miss) {
   GetWeakValue(value, cell);
   JumpIfSmi(value, miss);
 }
 
 
+void MacroAssembler::GetMapConstructor(Register result, Register map,
+                                       Register temp, Register temp2) {
+  Label done, loop;
+  ldr(result, FieldMemOperand(map, Map::kConstructorOrBackPointerOffset));
+  bind(&loop);
+  CompareObjectType(result, temp, temp2, MAP_TYPE);
+  b(ne, &done);
+  ldr(result, FieldMemOperand(result, Map::kConstructorOrBackPointerOffset));
+  b(&loop);
+  bind(&done);
+}
+
+
 void MacroAssembler::TryGetFunctionPrototype(Register function,
                                              Register result,
                                              Register scratch,
                                              Label* miss,
                                              bool miss_on_bound_function) {
   Label non_instance;
   if (miss_on_bound_function) {
     // Check that the receiver isn't a smi.
     JumpIfSmi(function, miss);
 
@@ skipping 33 matching lines @@
 
   // Get the prototype from the initial map.
   ldr(result, FieldMemOperand(result, Map::kPrototypeOffset));
 
   if (miss_on_bound_function) {
     jmp(&done);
 
     // Non-instance prototype: Fetch prototype from constructor field
     // in initial map.
     bind(&non_instance);
-    ldr(result, FieldMemOperand(result, Map::kConstructorOffset));
+    ldr(result, FieldMemOperand(result, Map::kConstructorOrBackPointerOffset));
   }
 
   // All done.
   bind(&done);
 }
 
 
 void MacroAssembler::CallStub(CodeStub* stub,
                               TypeFeedbackId ast_id,
                               Condition cond) {
@@ skipping 1616 matching lines @@
     }
   }
   if (mag.shift > 0) mov(result, Operand(result, ASR, mag.shift));
   add(result, result, Operand(dividend, LSR, 31));
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM