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// Copyright 2013 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "hydrogen-dce.h"
#include "v8.h"
namespace v8 {
namespace internal {
bool HDeadCodeEliminationPhase::MarkLive(HValue* ref, HValue* instr) {
if (instr->CheckFlag(HValue::kIsLive)) return false;
instr->SetFlag(HValue::kIsLive);
if (FLAG_trace_dead_code_elimination) {
HeapStringAllocator allocator;
StringStream stream(&allocator);
if (ref != NULL) {
ref->PrintTo(&stream);
} else {
stream.Add("root ");
}
stream.Add(" -> ");
instr->PrintTo(&stream);
PrintF("[MarkLive %s]\n", *stream.ToCString());
}
return true;
}
void HDeadCodeEliminationPhase::MarkLiveInstructions() {
ZoneList<HValue*> worklist(graph()->blocks()->length(), zone());
// Mark initial root instructions for dead code elimination.
for (int i = 0; i < graph()->blocks()->length(); ++i) {
HBasicBlock* block = graph()->blocks()->at(i);
for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
HInstruction* instr = it.Current();
if (instr->CannotBeEliminated() && MarkLive(NULL, instr)) {
worklist.Add(instr, zone());
}
}
for (int j = 0; j < block->phis()->length(); j++) {
HPhi* phi = block->phis()->at(j);
if (phi->CannotBeEliminated() && MarkLive(NULL, phi)) {
worklist.Add(phi, zone());
}
}
}
// Transitively mark all inputs of live instructions live.
while (!worklist.is_empty()) {
HValue* instr = worklist.RemoveLast();
for (int i = 0; i < instr->OperandCount(); ++i) {
if (MarkLive(instr, instr->OperandAt(i))) {
worklist.Add(instr->OperandAt(i), zone());
}
}
}
}
void HDeadCodeEliminationPhase::RemoveDeadInstructions() {
ZoneList<HPhi*> worklist(graph()->blocks()->length(), zone());
// Remove any instruction not marked kIsLive.
for (int i = 0; i < graph()->blocks()->length(); ++i) {
HBasicBlock* block = graph()->blocks()->at(i);
for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
HInstruction* instr = it.Current();
if (!instr->CheckFlag(HValue::kIsLive)) {
// Instruction has not been marked live; assume it is dead and remove.
// TODO(titzer): we don't remove constants because some special ones
// might be used by later phases and are assumed to be in the graph
if (!instr->IsConstant()) instr->DeleteAndReplaceWith(NULL);
} else {
// Clear the liveness flag to leave the graph clean for the next DCE.
instr->ClearFlag(HValue::kIsLive);
}
}
// Collect phis that are dead and remove them in the next pass.
for (int j = 0; j < block->phis()->length(); j++) {
HPhi* phi = block->phis()->at(j);
if (!phi->CheckFlag(HValue::kIsLive)) {
worklist.Add(phi, zone());
} else {
phi->ClearFlag(HValue::kIsLive);
}
}
}
// Process phis separately to avoid simultaneously mutating the phi list.
while (!worklist.is_empty()) {
HPhi* phi = worklist.RemoveLast();
HBasicBlock* block = phi->block();
phi->DeleteAndReplaceWith(NULL);
if (phi->HasMergedIndex()) {
block->RecordDeletedPhi(phi->merged_index());
}
}
}
} } // namespace v8::internal
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