ad412d046b
Removed a superfluous space on the way. BUG=v8:3679 LOG=y Review URL: https://codereview.chromium.org/843673004 Cr-Commit-Position: refs/heads/master@{#25988}
106 lines
3.3 KiB
C++
106 lines
3.3 KiB
C++
// Copyright 2013 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "src/hydrogen-dce.h"
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#include "src/v8.h"
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namespace v8 {
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namespace internal {
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void HDeadCodeEliminationPhase::MarkLive(
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HValue* instr, ZoneList<HValue*>* worklist) {
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if (instr->CheckFlag(HValue::kIsLive)) return; // Already live.
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if (FLAG_trace_dead_code_elimination) PrintLive(NULL, instr);
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// Transitively mark all inputs of live instructions live.
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worklist->Add(instr, zone());
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while (!worklist->is_empty()) {
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HValue* instr = worklist->RemoveLast();
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instr->SetFlag(HValue::kIsLive);
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for (int i = 0; i < instr->OperandCount(); ++i) {
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HValue* input = instr->OperandAt(i);
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if (!input->CheckFlag(HValue::kIsLive)) {
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input->SetFlag(HValue::kIsLive);
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worklist->Add(input, zone());
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if (FLAG_trace_dead_code_elimination) PrintLive(instr, input);
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}
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}
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}
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}
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void HDeadCodeEliminationPhase::PrintLive(HValue* ref, HValue* instr) {
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AllowHandleDereference allow_deref;
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OFStream os(stdout);
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os << "[MarkLive ";
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if (ref != NULL) {
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os << *ref;
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} else {
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os << "root";
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}
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os << " -> " << *instr << "]" << std::endl;
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}
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void HDeadCodeEliminationPhase::MarkLiveInstructions() {
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ZoneList<HValue*> worklist(10, zone());
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// Transitively mark all live instructions, starting from roots.
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for (int i = 0; i < graph()->blocks()->length(); ++i) {
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HBasicBlock* block = graph()->blocks()->at(i);
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for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
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HInstruction* instr = it.Current();
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if (instr->CannotBeEliminated()) MarkLive(instr, &worklist);
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}
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for (int j = 0; j < block->phis()->length(); j++) {
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HPhi* phi = block->phis()->at(j);
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if (phi->CannotBeEliminated()) MarkLive(phi, &worklist);
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}
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}
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DCHECK(worklist.is_empty()); // Should have processed everything.
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}
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void HDeadCodeEliminationPhase::RemoveDeadInstructions() {
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ZoneList<HPhi*> worklist(graph()->blocks()->length(), zone());
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// Remove any instruction not marked kIsLive.
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for (int i = 0; i < graph()->blocks()->length(); ++i) {
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HBasicBlock* block = graph()->blocks()->at(i);
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for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
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HInstruction* instr = it.Current();
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if (!instr->CheckFlag(HValue::kIsLive)) {
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// Instruction has not been marked live, so remove it.
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instr->DeleteAndReplaceWith(NULL);
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} else {
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// Clear the liveness flag to leave the graph clean for the next DCE.
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instr->ClearFlag(HValue::kIsLive);
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}
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}
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// Collect phis that are dead and remove them in the next pass.
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for (int j = 0; j < block->phis()->length(); j++) {
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HPhi* phi = block->phis()->at(j);
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if (!phi->CheckFlag(HValue::kIsLive)) {
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worklist.Add(phi, zone());
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} else {
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phi->ClearFlag(HValue::kIsLive);
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}
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}
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}
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// Process phis separately to avoid simultaneously mutating the phi list.
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while (!worklist.is_empty()) {
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HPhi* phi = worklist.RemoveLast();
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HBasicBlock* block = phi->block();
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phi->DeleteAndReplaceWith(NULL);
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if (phi->HasMergedIndex()) {
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block->RecordDeletedPhi(phi->merged_index());
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}
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}
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}
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} } // namespace v8::internal
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