Enables optimization on MIPS

runtime/vm/assembler_mips.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/assembler.h"
 #include "vm/runtime_entry.h"
 #include "vm/simulator.h"
@@ skipping 186 matching lines @@
   return object_pool_.Length() - 1;
 }
 
 
 void Assembler::PushObject(const Object& object) {
   LoadObject(TMP1, object);
   Push(TMP1);
 }
 
 
-void Assembler::CompareObject(Register rd, Register rn, const Object& object) {
+void Assembler::CompareObject(Register rd1, Register rd2,
+                              Register rn, const Object& object) {
   ASSERT(rn != TMP1);
+  ASSERT(rd1 != TMP1);
+  ASSERT(rd1 != rd2);
   LoadObject(TMP1, object);
-  subu(rd, rn, TMP1);
+  slt(rd1, rn, TMP1);
+  slt(rd2, TMP1, rn);

[regis, 2013/05/24 22:32:59]

Do you always need both results? Would it make sense to split this function?

[zra, 2013/05/24 23:25:47]

Not always, no. Both are needed only when the object is a Smi and the comparison
is something other than == or !=. The problem is that in
ControlInstruction::EmitBranchOnCondition you won't know which of the split
CompareObjects came before, if I understand your suggestion correctly.

 }
 
 
 // Preserves object and value registers.
 void Assembler::StoreIntoObjectFilterNoSmi(Register object,
                                            Register value,
                                            Label* no_update) {
   COMPILE_ASSERT((kNewObjectAlignmentOffset == kWordSize) &&
                  (kOldObjectAlignmentOffset == 0), young_alignment);
 
@@ skipping 357 matching lines @@
     Emit(reinterpret_cast<int32_t>(message));
     Bind(&msg);
     break_(Instr::kMsgMessageCode);
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS