Eliminate redundant smi checks

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index e69b66c1ba2d69336bdecd7ddf1021113f3a5772..1397f89243c004d538dc687838258cb59a6e7eab 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -1697,8 +1697,9 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
     } else {
       ASSERT(to.IsInteger32());
       LOperand* value = UseRegister(instr->value());
-      bool needs_check = !instr->value()->type().IsSmi();
-      if (needs_check) {
+      if (instr->value()->IsValueTaggedSmi()) {
+        return DefineSameAsFirst(new(zone()) LSmiUntag(value, false));
+      } else {
         bool truncating = instr->CanTruncateToInt32();
         LOperand* xmm_temp =
             (truncating && CpuFeatures::IsSupported(SSE3))
@@ -1706,8 +1707,6 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
             : FixedTemp(xmm1);
         LTaggedToI* res = new(zone()) LTaggedToI(value, xmm_temp);
         return AssignEnvironment(DefineSameAsFirst(res));
-      } else {
-        return DefineSameAsFirst(new(zone()) LSmiUntag(value, needs_check));
       }
     }
   } else if (from.IsDouble()) {