Remove redundant loads in DoCheckMaps

src/arm/lithium-codegen-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // 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 4816 matching lines @@
   DeoptimizeIf(ne, instr->environment());
 }
 
 
 void LCodeGen::DoCheckMapCommon(Register reg,
                                 Register scratch,
                                 Handle<Map> map,
                                 CompareMapMode mode,
                                 LEnvironment* env) {
   Label success;
   __ CompareMap(reg, scratch, map, &success, mode);

[danno, 2012/11/07 22:42:41]

Why not pass in the map register here, too (to avoid extra loads of the map),
since the optimization you applied below applies all callers of this helper
method, too.

   DeoptimizeIf(ne, env);
   __ bind(&success);
 }
 
 
 void LCodeGen::DoCheckMaps(LCheckMaps* instr) {
   Register scratch = scratch0();
   LOperand* input = instr->value();
   ASSERT(input->IsRegister());
   Register reg = ToRegister(input);
 
   Label success;
   SmallMapList* map_set = instr->hydrogen()->map_set();
+  __ ldr(scratch, FieldMemOperand(reg, HeapObject::kMapOffset));
   for (int i = 0; i < map_set->length() - 1; i++) {
     Handle<Map> map = map_set->at(i);
-    __ CompareMap(reg, scratch, map, &success, REQUIRE_EXACT_MAP);
+    __ CompareMap(scratch, map, &success, REQUIRE_EXACT_MAP);
     __ b(eq, &success);
   }
   Handle<Map> map = map_set->last();
   DoCheckMapCommon(reg, scratch, map, REQUIRE_EXACT_MAP, instr->environment());
   __ bind(&success);
 }
 
 
 void LCodeGen::DoClampDToUint8(LClampDToUint8* instr) {
   DoubleRegister value_reg = ToDoubleRegister(instr->unclamped());
@@ skipping 816 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal