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

src/mips/lithium-codegen-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.7
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2639 matching lines @@
     // Faster code path to avoid two compares: subtract lower bound from the
     // actual type and do a signed compare with the width of the type range.
     __ GetObjectType(input, temp, temp2);
     __ Subu(temp2, temp2, Operand(FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
     __ Branch(is_false, gt, temp2, Operand(LAST_NONCALLABLE_SPEC_OBJECT_TYPE -
                                            FIRST_NONCALLABLE_SPEC_OBJECT_TYPE));
   }
 
   // Now we are in the FIRST-LAST_NONCALLABLE_SPEC_OBJECT_TYPE range.
   // Check if the constructor in the map is a function.
-  __ lw(temp, FieldMemOperand(temp, Map::kConstructorOffset));
+  Register instance_type = scratch1();
+  DCHECK(!instance_type.is(temp));
+  DCHECK(!instance_type.is(temp2));

[Jakob Kummerow, 2015/02/25 09:39:45]

DBC: having |instance_type| and |temp2| overlap shouldn't matter, since the code
below doesn't care about the contents of |temp2|.

+  __ GetMapConstructor(temp, temp, temp2, instance_type);
 
   // Objects with a non-function constructor have class 'Object'.
-  __ GetObjectType(temp, temp2, temp2);
   if (String::Equals(class_name, isolate()->factory()->Object_string())) {
-    __ Branch(is_true, ne, temp2, Operand(JS_FUNCTION_TYPE));
+    __ Branch(is_true, ne, instance_type, Operand(JS_FUNCTION_TYPE));
   } else {
-    __ Branch(is_false, ne, temp2, Operand(JS_FUNCTION_TYPE));
+    __ Branch(is_false, ne, instance_type, Operand(JS_FUNCTION_TYPE));
   }
 
   // temp now contains the constructor function. Grab the
   // instance class name from there.
   __ lw(temp, FieldMemOperand(temp, JSFunction::kSharedFunctionInfoOffset));
   __ lw(temp, FieldMemOperand(temp,
                                SharedFunctionInfo::kInstanceClassNameOffset));
   // The class name we are testing against is internalized since it's a literal.
   // The name in the constructor is internalized because of the way the context
   // is booted.  This routine isn't expected to work for random API-created
@@ skipping 3353 matching lines @@
   __ li(at, scope_info);
   __ Push(at, ToRegister(instr->function()));
   CallRuntime(Runtime::kPushBlockContext, 2, instr);
   RecordSafepoint(Safepoint::kNoLazyDeopt);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal