Land two patches by Andy Wingo.

src/hydrogen-instructions.cc

 // Copyright 2011 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 463 matching lines @@
     } else {
       removed->set_tail(new_value->use_list_);
       new_value->use_list_ = removed;
     }
   }
 }
 
 
 void HValue::AddNewRange(Range* r) {
   if (!HasRange()) ComputeInitialRange();
-  if (!HasRange()) range_ = new Range();
   ASSERT(HasRange());
   r->StackUpon(range_);
   range_ = r;
 }
 
 
 void HValue::RemoveLastAddedRange() {
   ASSERT(HasRange());
   ASSERT(range_->next() != NULL);
   range_ = range_->next();
@@ skipping 360 matching lines @@
 void HInstanceOf::PrintDataTo(StringStream* stream) {
   left()->PrintNameTo(stream);
   stream->Add(" ");
   right()->PrintNameTo(stream);
   stream->Add(" ");
   context()->PrintNameTo(stream);
 }
 
 
 Range* HValue::InferRange() {
-  if (representation().IsTagged()) {
-    // Tagged values are always in int32 range when converted to integer,
-    // but they can contain -0.
+  if (representation().IsInteger32 ()) {
+    // Untagged integer32 cannot be -0.
+    return new Range ();
+  } else {
+    // Tagged values, untagged doubles, and values with unknown representation
+    // can contain -0.
     Range* result = new Range();
     result->set_can_be_minus_zero(true);
     return result;
-  } else if (representation().IsNone()) {
-    return NULL;
-  } else {
-    // Untagged integer32 cannot be -0 and we don't compute ranges for
-    // untagged doubles.
-    return new Range();
   }
 }
 
 
 Range* HConstant::InferRange() {
   if (has_int32_value_) {
-    Range* result = new Range(int32_value_, int32_value_);
-    result->set_can_be_minus_zero(false);
-    return result;
+    return new Range(int32_value_, int32_value_);
   }
   return HValue::InferRange();
 }
 
 
 Range* HPhi::InferRange() {
   if (representation().IsInteger32()) {
     if (block()->IsLoopHeader()) {
-      Range* range = new Range(kMinInt, kMaxInt);
-      return range;
+      return new Range();
     } else {
       Range* range = OperandAt(0)->range()->Copy();
       for (int i = 1; i < OperandCount(); ++i) {
         range->Union(OperandAt(i)->range());
       }
       return range;
     }
   } else {
     return HValue::InferRange();
   }
@@ skipping 935 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal