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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 */
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