MIPS: Eliminate Smi check when changing from Smi to Integer32

Port r16362 (6dd68a5c)

BUG=

Review URL: https://codereview.chromium.org/23462004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16375 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-mips.cc

@@ -1844,11 +1844,12 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
       ASSERT(to.IsInteger32());
       LOperand* value = NULL;
       LInstruction* res = NULL;
-      if (instr->value()->type().IsSmi()) {
-        value = UseRegisterAtStart(instr->value());
+      HValue* val = instr->value();
+      if (val->type().IsSmi() || val->representation().IsSmi()) {
+        value = UseRegisterAtStart(val);
         res = DefineAsRegister(new(zone()) LSmiUntag(value, false));
       } else {
-        value = UseRegister(instr->value());
+        value = UseRegister(val);
         LOperand* temp1 = TempRegister();
         LOperand* temp2 = instr->CanTruncateToInt32() ? TempRegister()
                                                       : NULL;