Improve our simple elimination of hole checks.

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 1463 matching lines @@
 
 
 void HLoadKeyedFastDoubleElement::PrintDataTo(StringStream* stream) {
   elements()->PrintNameTo(stream);
   stream->Add("[");
   key()->PrintNameTo(stream);
   stream->Add("]");
 }
 
 
-bool HLoadKeyedFastDoubleElement::RequiresHoleCheck() const {
-  return true;
-}
-
-
 void HLoadKeyedGeneric::PrintDataTo(StringStream* stream) {
   object()->PrintNameTo(stream);
   stream->Add("[");
   key()->PrintNameTo(stream);
   stream->Add("]");
 }
 
 
 void HLoadKeyedSpecializedArrayElement::PrintDataTo(
     StringStream* stream) {
@@ skipping 133 matching lines @@
   }
   stream->Add("[");
   key()->PrintNameTo(stream);
   stream->Add("] = ");
   value()->PrintNameTo(stream);
 }
 
 
 void HLoadGlobalCell::PrintDataTo(StringStream* stream) {
   stream->Add("[%p]", *cell());
-  if (check_hole_value()) stream->Add(" (deleteable/read-only)");
+  if (deleteable_or_const()) stream->Add(" (deleteable/read-only)");
+}
+
+
+bool HLoadGlobalCell::RequiresHoleCheck() const {
+  if (!deleteable_or_const()) return false;
+  for (HUseIterator it(uses()); !it.Done(); it.Advance()) {
+    HValue* use = it.value();
+    if (!use->IsChange()) return true;
+  }
+  return false;
 }
 
 
 void HLoadGlobalGeneric::PrintDataTo(StringStream* stream) {
   stream->Add("%o ", *name());
 }
 
 
 void HStoreGlobalCell::PrintDataTo(StringStream* stream) {
   stream->Add("[%p] = ", *cell());
   value()->PrintNameTo(stream);
+  if (deleteable_or_const()) stream->Add(" (deleteable/read-only)");
 }
 
 
 void HStoreGlobalGeneric::PrintDataTo(StringStream* stream) {
   stream->Add("%o = ", *name());
   value()->PrintNameTo(stream);
 }
 
 
 void HLoadContextSlot::PrintDataTo(StringStream* stream) {
@@ skipping 262 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal