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

src/arm64/lithium-codegen-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"
 
 #include "src/arm64/lithium-codegen-arm64.h"
 #include "src/arm64/lithium-gap-resolver-arm64.h"
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 2420 matching lines @@
     __ B(lt, false_label);
     __ B(eq, true_label);
     __ Cmp(scratch1, LAST_SPEC_OBJECT_TYPE);
     __ B(eq, true_label);
   } else {
     __ IsObjectJSObjectType(input, map, scratch1, false_label);
   }
 
   // Now we are in the FIRST-LAST_NONCALLABLE_SPEC_OBJECT_TYPE range.
   // Check if the constructor in the map is a function.
-  __ Ldr(scratch1, FieldMemOperand(map, Map::kConstructorOffset));
-
+  {
+    UseScratchRegisterScope temps(masm());
+    Register instance_type = temps.AcquireX();
+    __ GetMapConstructor(scratch1, map, scratch2, instance_type);
+    __ Cmp(instance_type, JS_FUNCTION_TYPE);
+  }
   // Objects with a non-function constructor have class 'Object'.
   if (String::Equals(class_name, isolate()->factory()->Object_string())) {
-    __ JumpIfNotObjectType(
-        scratch1, scratch2, scratch2, JS_FUNCTION_TYPE, true_label);
+    __ B(ne, true_label);
   } else {
-    __ JumpIfNotObjectType(
-        scratch1, scratch2, scratch2, JS_FUNCTION_TYPE, false_label);
+    __ B(ne, false_label);
   }
 
   // The constructor function is in scratch1. Get its instance class name.
   __ Ldr(scratch1,
          FieldMemOperand(scratch1, JSFunction::kSharedFunctionInfoOffset));
   __ Ldr(scratch1,
          FieldMemOperand(scratch1,
                          SharedFunctionInfo::kInstanceClassNameOffset));
 
   // The class name we are testing against is internalized since it's a literal.
@@ skipping 3642 matching lines @@
   Handle<ScopeInfo> scope_info = instr->scope_info();
   __ Push(scope_info);
   __ Push(ToRegister(instr->function()));
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 
 } }  // namespace v8::internal