We don't need to track writes of

src/hydrogen-instructions.h

 // 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 2231 matching lines @@
 
 
 class HConstant: public HTemplateInstruction<0> {
  public:
   HConstant(Handle<Object> handle, Representation r);
 
   Handle<Object> handle() const { return handle_; }
 
   bool InOldSpace() const { return !HEAP->InNewSpace(*handle_); }
 
+  bool ImmortalImmovable() const {
+    Heap* heap = HEAP;
+    if (*handle_ == heap->undefined_value()) return true;
+    if (*handle_ == heap->null_value()) return true;
+    if (*handle_ == heap->true_value()) return true;
+    if (*handle_ == heap->false_value()) return true;
+    if (*handle_ == heap->the_hole_value()) return true;
+    return false;
+  }
+
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::None();
   }
 
   virtual bool IsConvertibleToInteger() const {
     if (handle_->IsSmi()) return true;
     if (handle_->IsHeapNumber() &&
         (HeapNumber::cast(*handle_)->value() ==
          static_cast<double>(NumberToInt32(*handle_)))) return true;
     return false;
@@ skipping 1061 matching lines @@
     HLoadContextSlot* b = HLoadContextSlot::cast(other);
     return (slot_index() == b->slot_index());
   }
 
  private:
   int slot_index_;
 };
 
 
 static inline bool StoringValueNeedsWriteBarrier(HValue* value) {
   // TODO(gc) On bleeding edge we omit write barrier when we are

[fschneider, 2011/09/08 19:57:43]

This TODO can be removed as well (or changed into a comment).

   // storing old space constant. We can't allow such an optimization
   // on GC branch.
-  return !value->type().IsSmi();
+  return !value->type().IsBoolean()
+      && !value->type().IsSmi()
+      && !(value->IsConstant() && HConstant::cast(value)->ImmortalImmovable());
 }
 
 
 class HStoreContextSlot: public HTemplateInstruction<2> {
  public:
   HStoreContextSlot(HValue* context, int slot_index, HValue* value)
       : slot_index_(slot_index) {
     SetOperandAt(0, context);
     SetOperandAt(1, value);
     SetFlag(kChangesContextSlots);
@@ skipping 845 matching lines @@
 
   DECLARE_CONCRETE_INSTRUCTION(In)
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_