Introduce %_IsMinusZero.

src/hydrogen-minus-zero.cc

 // Copyright 2013 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 31 matching lines @@
         Representation from = change->value()->representation();
         ASSERT(from.Equals(change->from()));
         if (from.IsSmiOrInteger32()) {
           ASSERT(change->to().IsTagged() ||
                  change->to().IsDouble() ||
                  change->to().IsSmiOrInteger32());
           ASSERT(visited_.IsEmpty());
           PropagateMinusZeroChecks(change->value());
           visited_.Clear();
         }
+      } else if (current->IsCompareMinusZeroAndBranch()) {
+        HCompareMinusZeroAndBranch* check =
+            HCompareMinusZeroAndBranch::cast(current);
+        if (check->value()->representation().IsSmiOrInteger32()) {
+          ASSERT(visited_.IsEmpty());
+          PropagateMinusZeroChecks(check->value());
+          visited_.Clear();
+        }
       }
     }
   }
 }
 
 
 void HComputeMinusZeroChecksPhase::PropagateMinusZeroChecks(HValue* value) {
   for (HValue* current = value;
        current != NULL && !visited_.Contains(current->id());
        current = current->EnsureAndPropagateNotMinusZero(&visited_)) {
@@ skipping 12 matching lines @@
     if (current->IsMul() || current->IsDiv() || current->IsMathMinMax()) {
       HBinaryOperation* operation = HBinaryOperation::cast(current);
       operation->EnsureAndPropagateNotMinusZero(&visited_);
       PropagateMinusZeroChecks(operation->left());
       PropagateMinusZeroChecks(operation->right());
     }
   }
 }
 
 } }  // namespace v8::internal