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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/. */
#include "frontend/WhileEmitter.h"
#include "frontend/BytecodeEmitter.h"
#include "frontend/SourceNotes.h"
#include "vm/Opcodes.h"
using namespace js;
using namespace js::frontend;
using mozilla::Maybe;
WhileEmitter::WhileEmitter(BytecodeEmitter* bce) : bce_(bce) {}
bool WhileEmitter::emitBody(const Maybe<uint32_t>& whilePos,
const Maybe<uint32_t>& bodyPos,
const Maybe<uint32_t>& endPos) {
MOZ_ASSERT(state_ == State::Start);
// Minimize bytecodes issued for one or more iterations by jumping to
// the condition below the body and closing the loop if the condition
// is true with a backward branch. For iteration count i:
//
// i test at the top test at the bottom
// = =============== ==================
// 0 ifeq-pass goto; ifne-fail
// 1 ifeq-fail; goto; ifne-pass goto; ifne-pass; ifne-fail
// 2 2*(ifeq-fail; goto); ifeq-pass goto; 2*ifne-pass; ifne-fail
// . . .
// N N*(ifeq-fail; goto); ifeq-pass goto; N*ifne-pass; ifne-fail
// If we have a single-line while, like "while (x) ;", we want to
// emit the line note before the initial goto, so that the
// debugger sees a single entry point. This way, if there is a
// breakpoint on the line, it will only fire once; and "next"ing
// will skip the whole loop. However, for the multi-line case we
// want to emit the line note after the initial goto, so that
// "cont" stops on each iteration -- but without a stop before the
// first iteration.
if (whilePos && endPos &&
bce_->parser->errorReporter().lineAt(*whilePos) ==
bce_->parser->errorReporter().lineAt(*endPos)) {
if (!bce_->updateSourceCoordNotes(*whilePos)) {
return false;
}
}
JumpTarget top = {-1};
if (!bce_->emitJumpTarget(&top)) {
return false;
}
loopInfo_.emplace(bce_, StatementKind::WhileLoop);
loopInfo_->setContinueTarget(top.offset);
if (!bce_->newSrcNote(SRC_WHILE, ¬eIndex_)) {
return false;
}
if (!loopInfo_->emitEntryJump(bce_)) {
return false;
}
if (!loopInfo_->emitLoopHead(bce_, bodyPos)) {
return false;
}
tdzCacheForBody_.emplace(bce_);
#ifdef DEBUG
state_ = State::Body;
#endif
return true;
}
bool WhileEmitter::emitCond(const Maybe<uint32_t>& condPos) {
MOZ_ASSERT(state_ == State::Body);
tdzCacheForBody_.reset();
if (!loopInfo_->emitLoopEntry(bce_, condPos)) {
return false;
}
#ifdef DEBUG
state_ = State::Cond;
#endif
return true;
}
bool WhileEmitter::emitEnd() {
MOZ_ASSERT(state_ == State::Cond);
if (!loopInfo_->emitLoopEnd(bce_, JSOP_IFNE)) {
return false;
}
if (!bce_->addTryNote(JSTRY_LOOP, bce_->stackDepth, loopInfo_->headOffset(),
loopInfo_->breakTargetOffset())) {
return false;
}
if (!bce_->setSrcNoteOffset(noteIndex_, SrcNote::While::BackJumpOffset,
loopInfo_->loopEndOffsetFromEntryJump())) {
return false;
}
if (!loopInfo_->patchBreaksAndContinues(bce_)) {
return false;
}
loopInfo_.reset();
#ifdef DEBUG
state_ = State::End;
#endif
return true;
}