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

src/arm64/macro-assembler-arm64.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_ARM64
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 3687 matching lines @@
 
 
 void MacroAssembler::LoadElementsKindFromMap(Register result, Register map) {
   // Load the map's "bit field 2".
   __ Ldrb(result, FieldMemOperand(map, Map::kBitField2Offset));
   // Retrieve elements_kind from bit field 2.
   DecodeField<Map::ElementsKindBits>(result);
 }
 
 
+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,
                                              BoundFunctionAction action) {
   DCHECK(!AreAliased(function, result, scratch));
 
   Label non_instance;
   if (action == kMissOnBoundFunction) {
     // Check that the receiver isn't a smi.
@@ skipping 31 matching lines @@
 
   // Get the prototype from the initial map.
   Ldr(result, FieldMemOperand(result, Map::kPrototypeOffset));
 
   if (action == kMissOnBoundFunction) {
     B(&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::CompareRoot(const Register& obj,
                                  Heap::RootListIndex index) {
   UseScratchRegisterScope temps(this);
@@ skipping 1491 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64