[turbofan] Add initial support for global specialization.

src/compiler/js-global-specialization.h

Index: src/compiler/js-global-specialization.h
diff --git a/src/compiler/js-global-specialization.h b/src/compiler/js-global-specialization.h
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+++ b/src/compiler/js-global-specialization.h
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+// Copyright 2015 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_GLOBAL_SPECIALIZATION_H_
+#define V8_COMPILER_JS_GLOBAL_SPECIALIZATION_H_
+
+#include "src/base/flags.h"
+#include "src/compiler/graph-reducer.h"
+#include "src/compiler/simplified-operator.h"
+
+namespace v8 {
+namespace internal {
+
+// Forward declarations.
+class CompilationDependencies;
+
+
+namespace compiler {
+
+// Forward declarations.
+class JSGraph;
+class JSOperatorBuilder;
+
+
+// Specializes a given JSGraph to a given GlobalObject, potentially constant
+// folding some {LoadGlobal} nodes or strength reducing some {StoreGlobal}
+// nodes.
+class JSGlobalSpecialization final : public AdvancedReducer {
+ public:
+  // Flags that control the mode of operation.
+  enum Flag {
+    kNoFlags = 0u,
+    kDeoptimizationEnabled = 1u << 0,
+    kTypingEnabled = 1u << 1
+  };
+  typedef base::Flags<Flag> Flags;
+
+  JSGlobalSpecialization(Editor* editor, JSGraph* jsgraph, Flags flags,
+                         Handle<GlobalObject> global_object,
+                         CompilationDependencies* dependencies);
+
+  Reduction Reduce(Node* node) final;
+
+ private:
+  Reduction ReduceJSLoadGlobal(Node* node);
+  Reduction ReduceJSStoreGlobal(Node* node);
+  Reduction ReduceLoadFromPropertyCell(Node* node,
+                                       Handle<PropertyCell> property_cell);
+  Reduction ReduceStoreToPropertyCell(Node* node,
+                                      Handle<PropertyCell> property_cell);
+
+  Reduction Replace(Node* node, Node* value, Node* effect = nullptr,
+                    Node* control = nullptr) {
+    ReplaceWithValue(node, value, effect, control);
+    return Changed(value);
+  }
+  Reduction Replace(Node* node, Handle<Object> value);
+
+  Graph* graph() const;
+  JSGraph* jsgraph() const { return jsgraph_; }
+  Isolate* isolate() const;
+  JSOperatorBuilder* javascript() const;
+  SimplifiedOperatorBuilder* simplified() { return &simplified_; }
+  Flags flags() const { return flags_; }
+  Handle<GlobalObject> global_object() const { return global_object_; }
+  CompilationDependencies* dependencies() const { return dependencies_; }
+
+  JSGraph* const jsgraph_;
+  Flags const flags_;
+  Handle<GlobalObject> global_object_;
+  CompilationDependencies* const dependencies_;
+  SimplifiedOperatorBuilder simplified_;
+
+  DISALLOW_COPY_AND_ASSIGN(JSGlobalSpecialization);
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_JS_GLOBAL_SPECIALIZATION_H_