Implement loop variable assignment analysis.

src/compiler/ast-loop-assignment-analyzer.h

Index: src/compiler/ast-loop-assignment-analyzer.h
diff --git a/src/compiler/ast-loop-assignment-analyzer.h b/src/compiler/ast-loop-assignment-analyzer.h
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+++ b/src/compiler/ast-loop-assignment-analyzer.h
@@ -0,0 +1,78 @@
+// 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_AST_LOOP_ASSIGNMENT_ANALYZER_H_
+#define V8_COMPILER_AST_LOOP_ASSIGNMENT_ANALYZER_H_
+
+#include "src/ast.h"
+#include "src/data-flow.h"
+#include "src/v8.h"
+#include "src/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+
+class Variable;
+class Scope;
+
+namespace compiler {
+
+// The result of analyzing loop assignments.
+class LoopAssignmentAnalysis : public ZoneObject {
+ public:
+  BitVector* GetVariablesAssignedInLoop(IterationStatement* loop) {
+    for (size_t i = 0; i < list_.size(); i++) {
+      // TODO(turbofan): hashmap or binary search for loop assignments.
+      if (list_[i].first == loop) return list_[i].second;
+    }
+    UNREACHABLE();  // should never ask for loops that aren't here!
+    return NULL;
+  }
+
+  int GetAssignmentCountForTesting(Scope* scope, Variable* var);
+
+ private:
+  friend class AstLoopAssignmentAnalyzer;
+  explicit LoopAssignmentAnalysis(Zone* zone) : list_(zone) {}
+  ZoneVector<std::pair<IterationStatement*, BitVector*>> list_;
+};
+
+
+// The class that performs loop assignment analysis by walking the AST.
+class AstLoopAssignmentAnalyzer : public AstVisitor {
+ public:
+  AstLoopAssignmentAnalyzer(Zone* zone, CompilationInfo* info);
+
+  LoopAssignmentAnalysis* Analyze();
+
+#define DECLARE_VISIT(type) virtual void Visit##type(type* node);
+  AST_NODE_LIST(DECLARE_VISIT)
+#undef DECLARE_VISIT
+
+  static int GetVariableIndex(Scope* scope, Variable* var);
+
+ private:
+  CompilationInfo* info_;
+  ZoneDeque<BitVector*> loop_stack_;
+  LoopAssignmentAnalysis* result_;
+
+  CompilationInfo* info() { return info_; }
+
+  void Enter(IterationStatement* loop);
+  void Exit(IterationStatement* loop);
+
+  void VisitIfNotNull(AstNode* node) {
+    if (node != NULL) Visit(node);
+  }
+
+  void AnalyzeAssignment(Variable* var);
+
+  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
+  DISALLOW_COPY_AND_ASSIGN(AstLoopAssignmentAnalyzer);
+};
+}
+}
+}  // namespace v8::internal::compiler
+
+#endif  // V8_COMPILER_AST_LOOP_ASSIGNMENT_ANALYZER_H_