TDZCheckCache.h - mozsearch

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-

 * vim: set ts=8 sts=2 et sw=2 tw=80:

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef frontend_TDZCheckCache_h

#define frontend_TDZCheckCache_h

#include "mozilla/Maybe.h"

#include "ds/Nestable.h"

#include "frontend/NameCollections.h"

namespace js {

namespace frontend {

struct BytecodeEmitter;

class TaggedParserAtomIndex;

enum MaybeCheckTDZ { CheckTDZ = true, DontCheckTDZ = false };

using CheckTDZMap = RecyclableNameMap<MaybeCheckTDZ>;

// A cache that tracks Temporal Dead Zone (TDZ) checks, so that any use of a

// lexical variable that's dominated by an earlier use, or by evaluation of its

// declaration (which will initialize it, perhaps to |undefined|), doesn't have

// to redundantly check that the lexical variable has been initialized

//

// Each basic block should have a TDZCheckCache in scope. Some NestableControl

// subclasses contain a TDZCheckCache.

//

// When a scope containing lexical variables is entered, all such variables are

// marked as CheckTDZ.  When a lexical variable is accessed, its entry is

// checked.  If it's CheckTDZ, a JSOp::CheckLexical is emitted and then the

// entry is marked DontCheckTDZ.  If it's DontCheckTDZ, no check is emitted

// because a prior check would have already failed.  Finally, because

// evaluating a lexical variable declaration initializes it (after any

// initializer is evaluated), evaluating a lexical declaration marks its entry

// as DontCheckTDZ.

class TDZCheckCache : public Nestable<TDZCheckCache> {

  PooledMapPtr<CheckTDZMap> cache_;

  [[nodiscard]] bool ensureCache(BytecodeEmitter* bce);

 public:

  explicit TDZCheckCache(BytecodeEmitter* bce);

  mozilla::Maybe<MaybeCheckTDZ> needsTDZCheck(BytecodeEmitter* bce,

                                              TaggedParserAtomIndex name);

  [[nodiscard]] bool noteTDZCheck(BytecodeEmitter* bce,

                                  TaggedParserAtomIndex name,

                                  MaybeCheckTDZ check);

};

} /* namespace frontend */

} /* namespace js */

#endif /* frontend_TDZCheckCache_h */