Range info propagation through HBoundsCheck.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/86233002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18078 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -947,6 +947,25 @@ void HBoundsCheck::InferRepresentation(HInferRepresentationPhase* h_infer) {
 }
 
 
+Range* HBoundsCheck::InferRange(Zone* zone) {
+  Representation r = representation();
+  if (r.IsSmiOrInteger32() && length()->HasRange()) {
+    int upper = length()->range()->upper() - (allow_equality() ? 0 : 1);
+    int lower = 0;
+
+    Range* result = new(zone) Range(lower, upper);
+    if (index()->HasRange()) {
+      result->Intersect(index()->range());
+    }
+
+    // In case of Smi representation, clamp result to Smi::kMaxValue.
+    if (r.IsSmi()) result->ClampToSmi();
+    return result;
+  }
+  return HValue::InferRange(zone);
+}
+
+
 void HBoundsCheckBaseIndexInformation::PrintDataTo(StringStream* stream) {
   stream->Add("base: ");
   base_index()->PrintNameTo(stream);

src/hydrogen-instructions.h

@@ -4029,6 +4029,8 @@ class HBoundsCheck V8_FINAL : public HTemplateInstruction<2> {
  protected:
   friend class HBoundsCheckBaseIndexInformation;
 
+  virtual Range* InferRange(Zone* zone) V8_OVERRIDE;
+
   virtual bool DataEquals(HValue* other) V8_OVERRIDE { return true; }
   bool skip_check_;
   HValue* base_;