Eliminate Smi check when changing from Smi to Integer32

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 31a06df0820cdf375c8fc6f0a1a6186e5c189355..7585e3f6fe30d3df314d99a2de04d1e3073be8fa 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1827,8 +1827,9 @@ LInstruction* LChunkBuilder::DoChange(HChange* instr) {
       return AssignEnvironment(DefineSameAsFirst(new(zone()) LCheckSmi(value)));
     } else {
       ASSERT(to.IsInteger32());
-      LOperand* value = UseRegister(instr->value());
-      if (instr->value()->type().IsSmi()) {
+      HValue* val = instr->value();
+      LOperand* value = UseRegister(val);
+      if (val->type().IsSmi() || val->representation().IsSmi()) {
         return DefineSameAsFirst(new(zone()) LSmiUntag(value, false));
       } else {
         bool truncating = instr->CanTruncateToInt32();