Adding visitors to regurgitate expression types or reset them.

src/ast-expression-visitor.h

+// 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_AST_EXPRESSION_VISITOR_H_
+#define V8_AST_EXPRESSION_VISITOR_H_
+
+#include "src/allocation.h"
+#include "src/ast.h"
+#include "src/effects.h"
+#include "src/scopes.h"
+#include "src/type-info.h"
+#include "src/types.h"
+#include "src/zone.h"
+
+namespace v8 {
+namespace internal {
+
+// A Visitor over a CompilationInfo's AST that invokes
+// VisitExpression on each expression node.
+
+class AstExpressionVisitor : public AstVisitor {
+ public:
+  explicit AstExpressionVisitor(CompilationInfo* info);
+
+  void* operator new(size_t size, Zone* zone) { return zone->New(size); }

[titzer, 2015/08/19 12:06:37]

I don't think you want to define your own new here. I think you want to extend
ZoneObject and use "new (zone)". It's not safer, but it's the V8 way.

[bradn, 2015/08/20 04:01:40]

Not groking. But maybe I'm missing something basic :-)

I can't inherit from ZoneObject without doing multiple inheritance here, as I
need to inherit from AstVisitor. Also, AstVisitor inherits from Embedded, which
in debug mode has a clashing operator new.

Currently this inlines ZoneObject in this class, so for instance in
TypingReseter::Run() I can do new (zone).
Or are you suggesting I do placement new there, ie:
new (zone->New(sizeof(TypingReseter))) TypingReseter ?

FWIW, this is the pattern used in typing.h and a few other places.

[rossberg, 2015/08/20 16:34:26]

Honestly, I don't know why typing.h does that. Why would one want to store a
visitor on the heap? You can just have it on the stack, as in

TypingReseter visitor(info);
visitor.VisitAll();

or even

TypingReseter(info).VisitAll();

+  void operator delete(void* pointer, Zone* zone) {}
+  void operator delete(void* pointer) {}
+
+  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
+
+ protected:
+  void VisitAll();
+  virtual void VisitExpression(Expression* expression) = 0;
+  int depth() { return depth_; }
+
+ private:
+  void VisitDeclarations(ZoneList<Declaration*>* d) override;
+  void VisitStatements(ZoneList<Statement*>* s) override;
+
+#define DECLARE_VISIT(type) virtual void Visit##type(type* node) override;
+  AST_NODE_LIST(DECLARE_VISIT)
+#undef DECLARE_VISIT
+
+  CompilationInfo* compilation_info_;
+  int depth_;
+
+  DISALLOW_COPY_AND_ASSIGN(AstExpressionVisitor);
+};
+}
+}  // namespace v8::internal
+
+#endif  // V8_AST_EXPRESSION_VISITOR_H_