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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_CForEmitter_h
#define frontend_CForEmitter_h
#include "mozilla/Attributes.h" // MOZ_STACK_CLASS
#include "mozilla/Maybe.h" // mozilla::Maybe
#include <stdint.h> // uint32_t
#include "frontend/BytecodeControlStructures.h" // LoopControl
#include "frontend/TDZCheckCache.h" // TDZCheckCache
namespace js {
namespace frontend {
struct BytecodeEmitter;
class EmitterScope;
// Class for emitting bytecode for c-style for block.
//
// Usage: (check for the return value is omitted for simplicity)
//
// `for (init; cond; update) body`
// CForEmitter cfor(this, headLexicalEmitterScopeForLet or nullptr);
// cfor.emitInit(Some(offset_of_init));
// emit(init); // without pushing value
// cfor.emitCond(Some(offset_of_cond));
// emit(cond);
// cfor.emitBody(CForEmitter::Cond::Present);
// emit(body);
// cfor.emitUpdate(CForEmitter::Update::Present, Some(offset_of_update)));
// emit(update);
// cfor.emitEnd(offset_of_for);
//
// `for (;;) body`
// CForEmitter cfor(this, nullptr);
// cfor.emitInit(Nothing());
// cfor.emitCond(Nothing());
// cfor.emitBody(CForEmitter::Cond::Missing);
// emit(body);
// cfor.emitUpdate(CForEmitter::Update::Missing, Nothing());
// cfor.emitEnd(offset_of_for);
//
class MOZ_STACK_CLASS CForEmitter {
// Basic structure of the bytecode (not complete).
//
// If `cond` is not empty:
// {init}
// loop:
// JSOp::LoopHead
// {cond}
// JSOp::JumpIfFalse break
// {body}
// continue:
// {update}
// JSOp::Goto loop
// break:
//
// If `cond` is empty:
// {init}
// loop:
// JSOp::LoopHead
// {body}
// continue:
// {update}
// JSOp::Goto loop
// break:
//
public:
enum class Cond { Missing, Present };
enum class Update { Missing, Present };
private:
BytecodeEmitter* bce_;
// Whether the c-style for loop has `cond` and `update`.
Cond cond_ = Cond::Missing;
Update update_ = Update::Missing;
mozilla::Maybe<LoopControl> loopInfo_;
// The lexical scope to be freshened for each iteration.
// See the comment in `emitCond` for more details.
//
// ### Scope freshening
//
// Each iteration of a `for (let V...)` loop creates a fresh loop variable
// binding for V, even if the loop is a C-style `for(;;)` loop:
//
// var funcs = [];
// for (let i = 0; i < 2; i++)
// funcs.push(function() { return i; });
// assertEq(funcs[0](), 0); // the two closures capture...
// assertEq(funcs[1](), 1); // ...two different `i` bindings
//
// This is implemented by "freshening" the implicit block -- changing the
// scope chain to a fresh clone of the instantaneous block object -- each
// iteration, just before evaluating the "update" in for(;;) loops.
//
// ECMAScript doesn't freshen in `for (const ...;;)`. Lack of freshening
// isn't directly observable in-language because `const`s can't be mutated,
// but it *can* be observed in the Debugger API.
const EmitterScope* headLexicalEmitterScopeForLet_;
mozilla::Maybe<TDZCheckCache> tdzCache_;
#ifdef DEBUG
// The state of this emitter.
//
// +-------+ emitInit +------+ emitCond +------+ emitBody +------+
// | Start |--------->| Init |--------->| Cond |--------->| Body |-+
// +-------+ +------+ +------+ +------+ |
// |
// +-------------------------------------+
// |
// | emitUpdate +--------+ emitEnd +-----+
// +----------->| Update |-------->| End |
// +--------+ +-----+
enum class State {
// The initial state.
Start,
// After calling emitInit.
Init,
// After calling emitCond.
Cond,
// After calling emitBody.
Body,
// After calling emitUpdate.
Update,
// After calling emitEnd.
End
};
State state_ = State::Start;
#endif
public:
CForEmitter(BytecodeEmitter* bce,
const EmitterScope* headLexicalEmitterScopeForLet);
// Parameters are the offset in the source code for each character below:
//
// for ( x = 10 ; x < 20 ; x ++ ) { f(x); }
// ^ ^ ^ ^
// | | | |
// | | | updatePos
// | | |
// | | condPos
// | |
// | initPos
// |
// forPos
//
// Can be Nothing() if not available.
[[nodiscard]] bool emitInit(const mozilla::Maybe<uint32_t>& initPos);
[[nodiscard]] bool emitCond(const mozilla::Maybe<uint32_t>& condPos);
[[nodiscard]] bool emitBody(Cond cond);
[[nodiscard]] bool emitUpdate(Update update,
const mozilla::Maybe<uint32_t>& updatePos);
[[nodiscard]] bool emitEnd(uint32_t forPos);
};
} /* namespace frontend */
} /* namespace js */
#endif /* frontend_CForEmitter_h */
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