Infer the range of Math.abs

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1290 matching lines @@
     case kMathExp: return "exp";
     case kMathSqrt: return "sqrt";
     case kMathPowHalf: return "pow-half";
     default:
       UNREACHABLE();
       return NULL;
   }
 }
 
 
+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;
+      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);

[Sven Panne, 2013/06/07 08:11:48]

Shorter and more readable:

new(zone) Range(spans_zero ? 0 : Min(Abs(lower), Abs(upper)),
                Max(Abs(lower), Abs(upper)))

[Toon Verwaest, 2013/06/07 08:18:02]

Done.

+      if (r.IsSmi()) result->ClampToSmi();
+      if (r.IsInteger32()) result->ClampToInt32();
+      return result;
+    }
+  }
+  return HValue::InferRange(zone);
+}
+
+
 void HUnaryMathOperation::PrintDataTo(StringStream* stream) {
   const char* name = OpName();
   stream->Add("%s ", name);
   value()->PrintNameTo(stream);
 }
 
 
 void HUnaryOperation::PrintDataTo(StringStream* stream) {
   value()->PrintNameTo(stream);
 }
@@ skipping 2483 matching lines @@
     case kBackingStore:
       if (!name_.is_null()) stream->Add(*String::cast(*name_)->ToCString());
       stream->Add("[backing-store]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal