Improve range analysis for smi phi

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index f746af54bd75d988c082802b459699666630c6a0..e227cea08bc681a2116eeb38742c91a12215a9d2 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -1761,9 +1761,12 @@ Range* HConstant::InferRange(Zone* zone) {
 
 
 Range* HPhi::InferRange(Zone* zone) {
-  if (representation().IsInteger32()) {
+  Representation r = representation();
+  if (r.IsSmiOrInteger32()) {
     if (block()->IsLoopHeader()) {
-      Range* range = new(zone) Range(kMinInt, kMaxInt);
+      Range* range = r.IsSmi()
+          ? new(zone) Range(Smi::kMinValue, Smi::kMaxValue)
+          : new(zone) Range(kMinInt, kMaxInt);
       return range;
     } else {
       Range* range = OperandAt(0)->range()->Copy(zone);