Make GVN side effect analysis more precise.

src/hydrogen.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 990 matching lines @@
   void Kill(int flags);
 
   void Add(HValue* value) {
     present_flags_ |= value->flags();
     Insert(value);
   }
 
   HValue* Lookup(HValue* value) const;
 
   HValueMap* Copy(Zone* zone) const {
-    return new(zone) HValueMap(this);
+    return new(zone) HValueMap(zone, this);
   }
 
+  bool IsEmpty() const { return count_ == 0; }
+
  private:
   // A linked list of HValue* values.  Stored in arrays.
   struct HValueMapListElement {
     HValue* value;
     int next;  // Index in the array of the next list element.
   };
   static const int kNil = -1;  // The end of a linked list
 
   // Must be a power of 2.
   static const int kInitialSize = 16;
 
-  explicit HValueMap(const HValueMap* other);
+  HValueMap(Zone* zone, const HValueMap* other);
 
   void Resize(int new_size);
   void ResizeLists(int new_size);
   void Insert(HValue* value);
   uint32_t Bound(uint32_t value) const { return value & (array_size_ - 1); }
 
   int array_size_;
   int lists_size_;
   int count_;  // The number of values stored in the HValueMap.
   int present_flags_;  // All flags that are in any value in the HValueMap.
@@ skipping 161 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_