ForInEmitter.h - mozsearch

Enable keyboard shortcuts

/* -*- 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_ForInEmitter_h

#define frontend_ForInEmitter_h

#include "mozilla/Attributes.h"

#include "mozilla/Maybe.h"

#include <stdint.h>

#include "frontend/BytecodeControlStructures.h"

#include "frontend/TDZCheckCache.h"

namespace js {

namespace frontend {

struct BytecodeEmitter;

class EmitterScope;

// Class for emitting bytecode for for-in loop.

//

// Usage: (check for the return value is omitted for simplicity)

//

//   `for (init in iterated) body`

//     // headLexicalEmitterScope: lexical scope for init

//     ForInEmitter forIn(this, headLexicalEmitterScope);

//     forIn.emitIterated();

//     emit(iterated);

//     forIn.emitInitialize();

//     emit(init);

//     forIn.emitBody();

//     emit(body);

//     forIn.emitEnd(offset_of_for);

//

class MOZ_STACK_CLASS ForInEmitter {

  BytecodeEmitter* bce_;

#ifdef DEBUG

  // The stack depth before emitting initialize code inside loop.

  int32_t loopDepth_ = 0;

#endif

  mozilla::Maybe<LoopControl> loopInfo_;

  // The lexical scope to be freshened for each iteration.  See the comment

  // in `emitBody` for more details.  Can be nullptr if there's no lexical

  // scope.

  const EmitterScope* headLexicalEmitterScope_;

  // Cache for the iterated value.

  // (The cache for the iteration body is inside `loopInfo_`)

//

  // The iterated value needs its own TDZCheckCache, separated from both the

  // enclosing block and the iteration body, in order to make the sanity check

  // in Ion work properly.

  // In term of the execution order, the TDZCheckCache for the iterated value

  // dominates the one for the iteration body, that means the checks in the

  // iteration body is dead, and we can optimize them away.  But the sanity

  // check in Ion doesn't know it's dead.

  // (see bug 1368360 for more context)

  mozilla::Maybe<TDZCheckCache> tdzCacheForIteratedValue_;

#ifdef DEBUG

  // The state of this emitter.

//

  // +-------+ emitIterated +----------+ emitInitialize +------------+

  // | Start |------------->| Iterated |--------------->| Initialize |-+

  // +-------+              +----------+                +------------+ |

  //                                                                   |

  //                                +----------------------------------+

  //                                |

  //                                | emitBody +------+ emitEnd  +-----+

  //                                +----------| Body |--------->| End |

  //                                           +------+          +-----+

  enum class State {

    // The initial state.

    Start,

    // After calling emitIterated.

    Iterated,

    // After calling emitInitialize.

    Initialize,

    // After calling emitBody.

    Body,

    // After calling emitEnd.

End

};

  State state_ = State::Start;

#endif

 public:

  ForInEmitter(BytecodeEmitter* bce,

               const EmitterScope* headLexicalEmitterScope);

  // Parameters are the offset in the source code for each character below:

//

  //   for ( var x in obj ) { ... }

  //   ^

  //   |

  //   forPos

  [[nodiscard]] bool emitIterated();

  [[nodiscard]] bool emitInitialize();

  [[nodiscard]] bool emitBody();

  [[nodiscard]] bool emitEnd(uint32_t forPos);

};

} /* namespace frontend */

} /* namespace js */

#endif /* frontend_ForInEmitter_h */