[compiler] Introduce a simple store-store elimination, disabled by default.

src/v8.gyp

 # 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 642 matching lines @@
         'compiler/simplified-lowering.cc',
         'compiler/simplified-lowering.h',
         'compiler/simplified-operator-reducer.cc',
         'compiler/simplified-operator-reducer.h',
         'compiler/simplified-operator.cc',
         'compiler/simplified-operator.h',
         'compiler/source-position.cc',
         'compiler/source-position.h',
         'compiler/state-values-utils.cc',
         'compiler/state-values-utils.h',
+        'compiler/store-store-elimination.cc',
+        'compiler/store-store-elimination.h',
         'compiler/tail-call-optimization.cc',
         'compiler/tail-call-optimization.h',
         'compiler/type-hint-analyzer.cc',
         'compiler/type-hint-analyzer.h',
         'compiler/type-hints.cc',
         'compiler/type-hints.h',
         'compiler/typer.cc',
         'compiler/typer.h',
         'compiler/value-numbering-reducer.cc',
         'compiler/value-numbering-reducer.h',
@@ skipping 1608 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }