[turbofan] Implement simplistic checkpoint reducer.

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 487 matching lines @@
         'compiler/ast-loop-assignment-analyzer.h',
         'compiler/basic-block-instrumentor.cc',
         'compiler/basic-block-instrumentor.h',
         'compiler/branch-elimination.cc',
         'compiler/branch-elimination.h',
         'compiler/bytecode-branch-analysis.cc',
         'compiler/bytecode-branch-analysis.h',
         'compiler/bytecode-graph-builder.cc',
         'compiler/bytecode-graph-builder.h',
         'compiler/c-linkage.cc',
+        'compiler/checkpoint-elimination.cc',
+        'compiler/checkpoint-elimination.h',
         'compiler/coalesced-live-ranges.cc',
         'compiler/coalesced-live-ranges.h',
         'compiler/code-generator-impl.h',
         'compiler/code-generator.cc',
         'compiler/code-generator.h',
         'compiler/code-assembler.cc',
         'compiler/code-assembler.h',
         'compiler/common-node-cache.cc',
         'compiler/common-node-cache.h',
         'compiler/common-operator-reducer.cc',
@@ skipping 1759 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }