Improve our simple elimination of hole checks.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
===================================================================
--- src/hydrogen-instructions.cc	(revision 9445)
+++ src/hydrogen-instructions.cc	(working copy)
@@ -1481,11 +1481,6 @@
 }
 
 
-bool HLoadKeyedFastDoubleElement::RequiresHoleCheck() const {
-  return true;
-}
-
-
 void HLoadKeyedGeneric::PrintDataTo(StringStream* stream) {
   object()->PrintNameTo(stream);
   stream->Add("[");
@@ -1639,10 +1634,20 @@
 
 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());
 }
@@ -1651,6 +1656,7 @@
 void HStoreGlobalCell::PrintDataTo(StringStream* stream) {
   stream->Add("[%p] = ", *cell());
   value()->PrintNameTo(stream);
+  if (deleteable_or_const()) stream->Add(" (deleteable/read-only)");
 }