| // 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); |
| block->RecordDeletedPhi(phi->merged_index()); |
| } |
| } |
| |
| } } // namespace v8::internal |