Adding a type vector to replace type cells.

src/feedbackslots.h

-// Copyright 2011 the V8 project authors. All rights reserved.
+// Copyright 2014 the V8 project authors. All rights reserved.
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-#ifndef V8_REWRITER_H_
-#define V8_REWRITER_H_
+#ifndef V8_FEEDBACKSLOTS_H_
+#define V8_FEEDBACKSLOTS_H_
+#include "ast.h"
 
 namespace v8 {
 namespace internal {
 
-class CompilationInfo;
-
-class Rewriter {
+class FeedbackSlotAllocator: public AstVisitor {
  public:
-  // Rewrite top-level code (ECMA 262 "programs") so as to conservatively
-  // include an assignment of the value of the last statement in the code to
-  // a compiler-generated temporary variable wherever needed.
+  // Allocate feedback slots for ast nodes that require them.
   //
   // Assumes code has been parsed and scopes have been analyzed.  Mutates the
   // AST, so the AST should not continue to be used in the case of failure.
-  static bool Rewrite(CompilationInfo* info);
+  static bool Run(CompilationInfo* info);
+
+ private:
+  explicit FeedbackSlotAllocator(Zone* zone) : used_(0) {

[danno, 2014/01/28 08:27:17]

I worry that the additional pass over the AST might be expensive, especially for
very short-running programs. E.g. did you measure SunSpider performance? 

[mvstanton, 2014/01/30 15:13:41]

Although it didn't appear to cost much (nodes in the cache, most likely, because
it's done after the scope analysis pass), it may be that walking over the AST is
too much. So I followed your advice elsewhere and created a list of deferred
nodes to process later.

+    InitializeAstVisitor(zone);
+  }
+
+  int slot_count() const { return used_; }
+
+  // AST node visit functions.
+#define DECLARE_VISIT(type) virtual void Visit##type(type* node) { \
+    used_ = node->ConsumeFeedbackSlots(isolate(), used_);          \
+    DoVisit##type(node);                                           \
+  }                                                                \
+  void DoVisit##type(type* node);
+  AST_NODE_LIST(DECLARE_VISIT)
+#undef DECLARE_VISIT
+
+  int used_;
+
+  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
+  DISALLOW_COPY_AND_ASSIGN(FeedbackSlotAllocator);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_REWRITER_H_