Add an assigned variables analysis....

src/data-flow.h

 // Copyright 2010 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 22 matching lines @@
 #include "ast.h"
 #include "compiler.h"
 
 namespace v8 {
 namespace internal {
 
 class BitVector BASE_EMBEDDED {
  public:
   explicit BitVector(int length)
       : length_(length), bits_(Vector<uint32_t>::New(1 + length / 32)) {
-    ASSERT(length > 0);
     for (int i = 0; i < bits_.length(); i++) {
       bits_[i] = 0;
     }
   }
 
   BitVector(const BitVector& other)
       : length_(other.length()),
         bits_(Vector<uint32_t>::New(1 + other.length() / 32)) {
     CopyFrom(other);
   }
@@ skipping 436 matching lines @@
   AST_NODE_LIST(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
   // Map for tracking the live variables.
   VarUseMap live_vars_;
 
   DISALLOW_COPY_AND_ASSIGN(LivenessAnalyzer);
 };
 
 
+// Computes the set of assigned variables and annotates variables proxies
+// that are trivial sub-expressions and for-loops where the loop variable
+// is guaranteed to be a smi.
+class AssignedVariablesAnalyzer : public AstVisitor {
+ public:
+  explicit AssignedVariablesAnalyzer(FunctionLiteral* fun);
+
+  void Analyze();
+
+ private:
+  Variable* FindSmiLoopVariable(ForStatement* stmt);
+
+  int BitIndex(Variable* var);
+
+  void RecordAssignedVar(Variable* var);
+
+  void MarkIfTrivial(Expression* expr);
+
+  // Visits an expression saving the accumulator before, clearing
+  // it before visting and restoring it after visiting.
+  void ProcessExpression(Expression* expr);
+
+  // AST node visit functions.
+#define DECLARE_VISIT(type) virtual void Visit##type(type* node);
+  AST_NODE_LIST(DECLARE_VISIT)
+#undef DECLARE_VISIT
+
+  FunctionLiteral* fun_;
+
+  // Accumulator for assigned variables set.
+  BitVector av_;
+
+  DISALLOW_COPY_AND_ASSIGN(AssignedVariablesAnalyzer);
+};
+
 } }  // namespace v8::internal
 
 
 #endif  // V8_DATAFLOW_H_