268 lines
9.9 KiB
C++
268 lines
9.9 KiB
C++
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// 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-environment-liveness.h"
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namespace v8 {
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namespace internal {
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EnvironmentSlotLivenessAnalyzer::EnvironmentSlotLivenessAnalyzer(
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HGraph* graph)
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: graph_(graph),
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zone_(graph->isolate()),
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zone_scope_(&zone_, DELETE_ON_EXIT),
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block_count_(graph->blocks()->length()),
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maximum_environment_size_(graph->maximum_environment_size()),
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collect_markers_(true),
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last_simulate_(NULL) {
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if (maximum_environment_size_ == 0) return;
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live_at_block_start_ =
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new(zone()) ZoneList<BitVector*>(block_count_, zone());
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first_simulate_ = new(zone()) ZoneList<HSimulate*>(block_count_, zone());
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first_simulate_invalid_for_index_ =
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new(zone()) ZoneList<BitVector*>(block_count_, zone());
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markers_ = new(zone())
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ZoneList<HEnvironmentMarker*>(maximum_environment_size_, zone());
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went_live_since_last_simulate_ =
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new(zone()) BitVector(maximum_environment_size_, zone());
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for (int i = 0; i < block_count_; ++i) {
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live_at_block_start_->Add(
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new(zone()) BitVector(maximum_environment_size_, zone()), zone());
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first_simulate_->Add(NULL, zone());
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first_simulate_invalid_for_index_->Add(
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new(zone()) BitVector(maximum_environment_size_, zone()), zone());
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}
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}
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void EnvironmentSlotLivenessAnalyzer::ZapEnvironmentSlot(int index,
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HSimulate* simulate) {
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int operand_index = simulate->ToOperandIndex(index);
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if (operand_index == -1) {
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simulate->AddAssignedValue(index, graph_->GetConstantUndefined());
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} else {
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simulate->SetOperandAt(operand_index, graph_->GetConstantUndefined());
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}
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}
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void EnvironmentSlotLivenessAnalyzer::ZapEnvironmentSlotsInSuccessors(
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HBasicBlock* block,
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BitVector* live) {
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// When a value is live in successor A but dead in B, we must
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// explicitly zap it in B.
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for (HSuccessorIterator it(block->end()); !it.Done(); it.Advance()) {
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HBasicBlock* successor = it.Current();
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int successor_id = successor->block_id();
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BitVector* live_in_successor = live_at_block_start_->at(successor_id);
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if (live_in_successor->Equals(*live)) continue;
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for (int i = 0; i < live->length(); ++i) {
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if (!live->Contains(i)) continue;
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if (live_in_successor->Contains(i)) continue;
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if (first_simulate_invalid_for_index_->at(successor_id)->Contains(i)) {
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continue;
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}
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HSimulate* simulate = first_simulate_->at(successor_id);
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if (simulate == NULL) continue;
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ASSERT(simulate->closure().is_identical_to(
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block->last_environment()->closure()));
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ZapEnvironmentSlot(i, simulate);
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}
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}
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}
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void EnvironmentSlotLivenessAnalyzer::ZapEnvironmentSlotsForInstruction(
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HEnvironmentMarker* marker) {
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if (!marker->CheckFlag(HValue::kEndsLiveRange)) return;
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HSimulate* simulate = marker->next_simulate();
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if (simulate != NULL) {
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ASSERT(simulate->closure().is_identical_to(marker->closure()));
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ZapEnvironmentSlot(marker->index(), simulate);
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}
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}
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void EnvironmentSlotLivenessAnalyzer::UpdateLivenessAtBlockEnd(
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HBasicBlock* block,
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BitVector* live) {
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// Liveness at the end of each block: union of liveness in successors.
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live->Clear();
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for (HSuccessorIterator it(block->end()); !it.Done(); it.Advance()) {
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live->Union(*live_at_block_start_->at(it.Current()->block_id()));
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}
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}
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void EnvironmentSlotLivenessAnalyzer::UpdateLivenessAtInstruction(
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HInstruction* instr,
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BitVector* live) {
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switch (instr->opcode()) {
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case HValue::kEnvironmentMarker: {
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HEnvironmentMarker* marker = HEnvironmentMarker::cast(instr);
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int index = marker->index();
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if (!live->Contains(index)) {
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marker->SetFlag(HValue::kEndsLiveRange);
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} else {
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marker->ClearFlag(HValue::kEndsLiveRange);
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}
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if (!went_live_since_last_simulate_->Contains(index)) {
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marker->set_next_simulate(last_simulate_);
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}
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if (marker->kind() == HEnvironmentMarker::LOOKUP) {
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live->Add(index);
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} else {
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ASSERT(marker->kind() == HEnvironmentMarker::BIND);
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live->Remove(index);
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went_live_since_last_simulate_->Add(index);
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}
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if (collect_markers_) {
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// Populate |markers_| list during the first pass.
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markers_->Add(marker, &zone_);
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}
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break;
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}
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case HValue::kLeaveInlined:
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// No environment values are live at the end of an inlined section.
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live->Clear();
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last_simulate_ = NULL;
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// The following ASSERTs guard the assumption used in case
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// kEnterInlined below:
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ASSERT(instr->next()->IsSimulate());
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ASSERT(instr->next()->next()->IsGoto());
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break;
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case HValue::kEnterInlined: {
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// Those environment values are live that are live at any return
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// target block. Here we make use of the fact that the end of an
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// inline sequence always looks like this: HLeaveInlined, HSimulate,
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// HGoto (to return_target block), with no environment lookups in
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// between (see ASSERTs above).
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HEnterInlined* enter = HEnterInlined::cast(instr);
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live->Clear();
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for (int i = 0; i < enter->return_targets()->length(); ++i) {
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int return_id = enter->return_targets()->at(i)->block_id();
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// When an AbnormalExit is involved, it can happen that the return
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// target block doesn't actually exist.
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if (return_id < live_at_block_start_->length()) {
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live->Union(*live_at_block_start_->at(return_id));
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}
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}
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last_simulate_ = NULL;
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break;
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}
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case HValue::kDeoptimize: {
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// Keep all environment slots alive.
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HDeoptimize* deopt = HDeoptimize::cast(instr);
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for (int i = deopt->first_local_index();
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i < deopt->first_expression_index(); ++i) {
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live->Add(i);
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}
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break;
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}
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case HValue::kSimulate:
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last_simulate_ = HSimulate::cast(instr);
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went_live_since_last_simulate_->Clear();
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break;
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default:
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break;
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}
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}
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void EnvironmentSlotLivenessAnalyzer::AnalyzeAndTrim() {
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HPhase phase("H_EnvironmentLivenessAnalysis", graph_);
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if (maximum_environment_size_ == 0) return;
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// Main iteration. Compute liveness of environment slots, and store it
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// for each block until it doesn't change any more. For efficiency, visit
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// blocks in reverse order and walk backwards through each block. We
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// need several iterations to propagate liveness through nested loops.
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BitVector* live = new(zone()) BitVector(maximum_environment_size_, zone());
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BitVector* worklist = new(zone()) BitVector(block_count_, zone());
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for (int i = 0; i < block_count_; ++i) {
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worklist->Add(i);
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}
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while (!worklist->IsEmpty()) {
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for (int block_id = block_count_ - 1; block_id >= 0; --block_id) {
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if (!worklist->Contains(block_id)) {
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continue;
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}
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worklist->Remove(block_id);
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last_simulate_ = NULL;
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HBasicBlock* block = graph_->blocks()->at(block_id);
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UpdateLivenessAtBlockEnd(block, live);
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for (HInstruction* instr = block->last(); instr != NULL;
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instr = instr->previous()) {
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UpdateLivenessAtInstruction(instr, live);
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}
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// Reached the start of the block, do necessary bookkeeping:
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// store computed information for this block and add predecessors
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// to the work list as necessary.
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first_simulate_->Set(block_id, last_simulate_);
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first_simulate_invalid_for_index_->at(block_id)->CopyFrom(
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*went_live_since_last_simulate_);
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if (live_at_block_start_->at(block_id)->UnionIsChanged(*live)) {
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for (int i = 0; i < block->predecessors()->length(); ++i) {
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worklist->Add(block->predecessors()->at(i)->block_id());
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}
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if (block->IsInlineReturnTarget()) {
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worklist->Add(block->inlined_entry_block()->block_id());
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}
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}
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}
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// Only collect bind/lookup instructions during the first pass.
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collect_markers_ = false;
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}
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// Analysis finished. Zap dead environment slots.
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for (int i = 0; i < markers_->length(); ++i) {
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ZapEnvironmentSlotsForInstruction(markers_->at(i));
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}
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for (int block_id = block_count_ - 1; block_id >= 0; --block_id) {
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HBasicBlock* block = graph_->blocks()->at(block_id);
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UpdateLivenessAtBlockEnd(block, live);
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ZapEnvironmentSlotsInSuccessors(block, live);
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}
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// Finally, remove the HEnvironment{Bind,Lookup} markers.
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for (int i = 0; i < markers_->length(); ++i) {
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markers_->at(i)->DeleteAndReplaceWith(NULL);
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}
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}
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} } // namespace v8::internal
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