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..2526599a4f1c9bd10f20f01f412e3bb3181c30da 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -1308,6 +1308,25 @@ 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 = lower < 0 && 0 < upper;

[Jakob Kummerow, 2013/06/07 08:21:05]

There's Range::CanBeZero(). It checks for '<=' instead of '<' for both
relations, but that shouldn't make a difference here.

+      Range* result =
+          new(zone) Range(spans_zero ? 0 : Min(abs(lower), abs(upper)),
+                          Max(abs(lower), abs(upper)));
+      if (r.IsSmi()) result->ClampToSmi();

[Jakob Kummerow, 2013/06/07 08:21:05]

Is this needed? Doesn't r.IsSmi() imply value()->representation().IsSmi(), which
in turn implies that value()->range() is within Smi range anyway?

+      if (r.IsInteger32()) result->ClampToInt32();
+      return result;
+    }
+  }
+  return HValue::InferRange(zone);
+}
+
+
 void HUnaryMathOperation::PrintDataTo(StringStream* stream) {
   const char* name = OpName();
   stream->Add("%s ", name);