MIPS: Fix performance regression on sunspider string-unpack-code.

src/mips/stub-cache-mips.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 1424 matching lines @@
     Code::StubType type,
     IcCheckType check) {
   Label miss;
 
   if (check == PROPERTY &&
       (kind() == Code::KEYED_LOAD_IC || kind() == Code::KEYED_STORE_IC)) {
     __ Branch(&miss, ne, this->name(), Operand(name));
   }
 
   Label number_case;
+  Register match = scratch1();
   Label* smi_target = IncludesNumberType(types) ? &number_case : &miss;
-  __ JumpIfSmi(receiver(), smi_target);
+  __ JumpIfSmi(receiver(), smi_target, match);  // Reg match is 0 if Smi.
 
-  Register map_reg = scratch1();
+  Register map_reg = scratch2();
 
   int receiver_count = types->length();
   int number_of_handled_maps = 0;
   __ lw(map_reg, FieldMemOperand(receiver(), HeapObject::kMapOffset));
   for (int current = 0; current < receiver_count; ++current) {
     Handle<HeapType> type = types->at(current);
     Handle<Map> map = IC::TypeToMap(*type, isolate());
     if (!map->is_deprecated()) {
       number_of_handled_maps++;
+      // Check map and tail call if there's a match.
+      // Separate compare from branch, to provide path for above JumpIfSmi().
+      __ Subu(match, map_reg, Operand(map));
       if (type->Is(HeapType::Number())) {
         ASSERT(!number_case.is_unused());
         __ bind(&number_case);
       }
       __ Jump(handlers->at(current), RelocInfo::CODE_TARGET,
-          eq, map_reg, Operand(map));
+          eq, match, Operand(zero_reg));
     }
   }
   ASSERT(number_of_handled_maps != 0);
 
   __ bind(&miss);
   TailCallBuiltin(masm(), MissBuiltin(kind()));
 
   // Return the generated code.
   InlineCacheState state =
       number_of_handled_maps > 1 ? POLYMORPHIC : MONOMORPHIC;
@@ skipping 77 matching lines @@
   // -----------------------------------
   TailCallBuiltin(masm, Builtins::kKeyedLoadIC_Miss);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS