d63c8e4dc3
BUG= R=jkummerow@chromium.org Review URL: https://codereview.chromium.org/31943002 git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17299 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
130 lines
4.7 KiB
C++
130 lines
4.7 KiB
C++
// Copyright 2013 the V8 project authors. All rights reserved.
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following
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// disclaimer in the documentation and/or other materials provided
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// with the distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "hydrogen-dce.h"
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#include "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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HeapStringAllocator allocator;
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StringStream stream(&allocator);
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if (ref != NULL) {
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ref->PrintTo(&stream);
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} else {
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stream.Add("root ");
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}
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stream.Add(" -> ");
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instr->PrintTo(&stream);
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PrintF("[MarkLive %s]\n", *stream.ToCString());
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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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ASSERT(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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