MIPS: Optimize Integer32ToSmi.

Port r18084 (426bc19)

Original commit message:
Optimize register constraints and code generated for Integer32ToSmi Lithium
instruction.

TEST=none
BUG=
R=gergely@homejinni.com

Review URL: https://codereview.chromium.org/88623004

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18089 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -4633,10 +4633,13 @@ void LCodeGen::DoInteger32ToSmi(LInteger32ToSmi* instr) {
   LOperand* output = instr->result();
   Register scratch = scratch0();
 
-  __ SmiTagCheckOverflow(ToRegister(output), ToRegister(input), scratch);
+  ASSERT(output->IsRegister());
   if (!instr->hydrogen()->value()->HasRange() ||
       !instr->hydrogen()->value()->range()->IsInSmiRange()) {
+    __ SmiTagCheckOverflow(ToRegister(output), ToRegister(input), scratch);
     DeoptimizeIf(lt, instr->environment(), scratch, Operand(zero_reg));
+  } else {
+    __ SmiTag(ToRegister(output), ToRegister(input));
   }
 }
 

src/mips/lithium-mips.cc

@@ -1951,8 +1951,8 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
       HValue* val = instr->value();
       LOperand* value = UseRegister(val);
       LInstruction* result = val->CheckFlag(HInstruction::kUint32)
-          ? DefineSameAsFirst(new(zone()) LUint32ToSmi(value))
-          : DefineSameAsFirst(new(zone()) LInteger32ToSmi(value));
+          ? DefineAsRegister(new(zone()) LUint32ToSmi(value))
+          : DefineAsRegister(new(zone()) LInteger32ToSmi(value));
       if (val->HasRange() && val->range()->IsInSmiRange()) {
         return result;
       }