introduce LTaggedToSmi

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 27a5672901f0cd3287e61b768b26dac8c03d4294..d1f22bd220398cff6e94865dfee86473422f24c4 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -1805,8 +1805,15 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
       LOperand* value = UseRegister(val);
       if (val->type().IsSmi()) {
         return DefineSameAsFirst(new(zone()) LDummyUse(value));
+      } else {
+        bool truncating = instr->CanTruncateToSmi();
+        LOperand* temp =
+            (CpuFeatures::IsSafeForSnapshot(SSE2) && !truncating)
+                ? FixedTemp(xmm1) : NULL;
+        LTaggedToSmi* res = new(zone()) LTaggedToSmi(UseRegister(val), temp);
+
+        return AssignEnvironment(DefineSameAsFirst(res));
       }
-      return AssignEnvironment(DefineSameAsFirst(new(zone()) LCheckSmi(value)));
     } else {
       ASSERT(to.IsInteger32());
       HValue* val = instr->value();