Infer the range of Math.abs

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index d3f1a9e09024c8f1643eb53bddc3b595b3953d3e..8d4211f1f0487a891d57fff958c4940c04ea6981 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -1308,6 +1308,29 @@ const char* HUnaryMathOperation::OpName() const {
 }
 
 
+Range* HUnaryMathOperation::InferRange(Zone* zone) {
+  Representation r = representation();
+  if (r.IsSmiOrInteger32() && value()->HasRange()) {
+    if (op() == kMathAbs) {
+      int upper = value()->range()->upper();
+      int lower = value()->range()->lower();
+      bool spans_zero = value()->range()->CanBeZero();
+      // Math.abs(kMinInt) overflows its representation, on which the
+      // instruction deopts. Hence clamp it to kMaxInt.
+      int abs_lower = lower == kMinInt ? kMaxInt : abs(kMinInt);

[Jakob Kummerow, 2013/06/07 09:02:33]

I think you need to do this same trick for abs_upper, or is it guaranteed that
upper != kMinInt?

+      Range* result =
+          new(zone) Range(spans_zero ? 0 : Min(abs_lower, abs(upper)),
+                          Max(abs_lower, abs(upper)));
+      // In case of Smi representation, clamp Math.abs(Smi::kMinValue) to
+      // Smi::kMaxValue.
+      if (r.IsSmi()) result->ClampToSmi();
+      return result;
+    }
+  }
+  return HValue::InferRange(zone);
+}
+
+
 void HUnaryMathOperation::PrintDataTo(StringStream* stream) {
   const char* name = OpName();
   stream->Add("%s ", name);