Remove purely informative definitions from the graph.

src/hydrogen.cc

 // 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 4366 matching lines @@
     for (int i = 0; i < block->phis()->length(); i++) {
       HPhi* phi = block->phis()->at(i);
       ASSERT(phi->ActualValue() == phi);
     }
 #endif
 
     for (HInstruction* instruction = block->first();
         instruction != NULL;
         instruction = instruction->next()) {
       if (instruction->ActualValue() != instruction) {
-        instruction->ReplaceAllUsesWith(instruction->ActualValue());
+        ASSERT(instruction->IsInformativeDefinition());
+        if (instruction->IsPurelyInformativeDefinition()) {
+          instruction->DeleteAndReplaceWith(instruction->RedefinedOperand());
+        } else {
+          instruction->ReplaceAllUsesWith(instruction->ActualValue());
+        }
       }
     }
   }
 }
 
 
 void HOptimizedGraphBuilder::AddPhi(HPhi* instr) {
   ASSERT(current_block() != NULL);
   current_block()->AddPhi(instr);
 }
@@ skipping 6269 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal