Lazy removal of dead HValues in GVN from use lists.

src/hydrogen-instructions.h

 // Copyright 2012 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 430 matching lines @@
   int16_t type_;
 };
 
 
 class HUseListNode: public ZoneObject {
  public:
   HUseListNode(HValue* value, int index, HUseListNode* tail)
       : tail_(tail), value_(value), index_(index) {
   }
 
-  HUseListNode* tail() const { return tail_; }
+  HUseListNode* tail();
   HValue* value() const { return value_; }
   int index() const { return index_; }
 
   void set_tail(HUseListNode* list) { tail_ = list; }
 
 #ifdef DEBUG
   void Zap() {
     tail_ = reinterpret_cast<HUseListNode*>(1);
     value_ = NULL;
     index_ = -1;
@@ skipping 61 matching lines @@
     // unnecessary recomputations. If an instruction sets this flag, it must
     // implement DataEquals(), which will be used to determine if other
     // occurrences of the instruction are indeed the same.
     kUseGVN,
     kCanOverflow,
     kBailoutOnMinusZero,
     kCanBeDivByZero,
     kDeoptimizeOnUndefined,
     kIsArguments,
     kTruncatingToInt32,
-    kLastFlag = kTruncatingToInt32
+    kIsDead,
+    kLastFlag = kIsDead
   };
 
   STATIC_ASSERT(kLastFlag < kBitsPerInt);
 
   static const int kChangesToDependsFlagsLeftShift = 1;
 
   static GVNFlagSet ConvertChangesToDependsFlags(GVNFlagSet flags) {
     return GVNFlagSet(flags.ToIntegral() << kChangesToDependsFlagsLeftShift);
   }
 
@@ skipping 4219 matching lines @@
   DECLARE_CONCRETE_INSTRUCTION(LoadFieldByIndex);
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_