[turbofan]: Add a context relaxer reducer

src/compiler/js-context-relaxation.h

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_COMPILER_JS_CONTEXT_RELAXATION_H_
+#define V8_COMPILER_JS_CONTEXT_RELAXATION_H_
+
+#include "src/code-factory.h"

[Michael Starzinger, 2015/07/20 08:09:49]

nit: The code-factory include shouldn't be necessary (at least not in the
header).

[danno, 2015/07/20 15:27:33]

Done

+#include "src/compiler/graph-reducer.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Ensures that operations that only need to access the native context use the
+// outer-most context rather than the specific context given by the AST graph
+// builder. This makes it possible to use they operations with context

[Michael Starzinger, 2015/07/20 08:09:49]

nit: s/they/these/

[danno, 2015/07/20 15:27:33]

Done

+// specialization (e.g. for generating stubs) without forcing inner contexts to
+// be embedded in generated code thus causing leaks.

[Michael Starzinger, 2015/07/20 08:09:49]

nit: ... and potentially using the wrong native context (i.e. stubs are shared
between native contexts).

[danno, 2015/07/20 15:27:33]

Done

+class JSContextRelaxation final : public Reducer {
+ public:
+  JSContextRelaxation() {}
+  ~JSContextRelaxation() final {}
+
+  Reduction Reduce(Node* node) final;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_JS_CONTEXT_RELAXATION_H_