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

src/arm64/lithium-codegen-arm64.cc

Index: src/arm64/lithium-codegen-arm64.cc
diff --git a/src/arm64/lithium-codegen-arm64.cc b/src/arm64/lithium-codegen-arm64.cc
index a95ae9ef116fa1ca3de44bbfb7f201efb7782bdf..2f9169812a8e0c63059f41b0f46b61e47fbb4411 100644
--- a/src/arm64/lithium-codegen-arm64.cc
+++ b/src/arm64/lithium-codegen-arm64.cc
@@ -2438,15 +2438,17 @@ void LCodeGen::DoClassOfTestAndBranch(LClassOfTestAndBranch* instr) {
 
   // 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.