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..5cea51c2d27aec7c446e5ca2847c9194a12e8643 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -1308,6 +1308,31 @@ 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.

[Toon Verwaest, 2013/06/07 09:00:48]

Done.

+      upper = abs(upper);
+      lower = abs(lower);
+      if (upper < lower) {
+        int temp = upper;
+        upper = lower;
+        lower = temp;
+      }
+      if (spans_zero) lower = 0;
+      Range* result = new(zone) Range(lower, upper);
+      if (r.IsSmi()) result->TruncateToSmi();

[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?

[Toon Verwaest, 2013/06/07 09:00:48]

Added a comment to explain it.

On 2013/06/07 08:21:05, Jakob wrote:

+      if (r.IsInteger32()) result->TruncateToInt32();
+      return result;
+    }
+  }
+  return HValue::InferRange(zone);
+}
+
+
 void HUnaryMathOperation::PrintDataTo(StringStream* stream) {
   const char* name = OpName();
   stream->Add("%s ", name);