Revision f230a1cf deps/v8/src/hydrogen-redundant-phi.cc
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namespace internal {
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void HRedundantPhiEliminationPhase::Run() {
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// We do a simple fixed point iteration without any work list, because |
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// machine-generated JavaScript can lead to a very dense Hydrogen graph with |
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// an enormous work list and will consequently result in OOM. Experiments |
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// showed that this simple algorithm is good enough, and even e.g. tracking |
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// the set or range of blocks to consider is not a real improvement. |
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bool need_another_iteration; |
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// Gather all phis from all blocks first. |
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const ZoneList<HBasicBlock*>* blocks(graph()->blocks()); |
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ZoneList<HPhi*> redundant_phis(blocks->length(), zone()); |
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do {
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need_another_iteration = false; |
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for (int i = 0; i < blocks->length(); ++i) {
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HBasicBlock* block = blocks->at(i); |
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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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HValue* replacement = phi->GetRedundantReplacement(); |
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if (replacement != NULL) {
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// Remember phi to avoid concurrent modification of the block's phis. |
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redundant_phis.Add(phi, zone()); |
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for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
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HValue* value = it.value(); |
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value->SetOperandAt(it.index(), replacement); |
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need_another_iteration |= value->IsPhi(); |
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} |
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} |
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} |
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for (int i = 0; i < redundant_phis.length(); i++) {
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block->RemovePhi(redundant_phis[i]); |
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} |
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redundant_phis.Clear(); |
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ZoneList<HPhi*> all_phis(blocks->length(), zone()); |
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for (int i = 0; i < blocks->length(); ++i) {
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HBasicBlock* block = blocks->at(i); |
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for (int j = 0; j < block->phis()->length(); j++) {
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all_phis.Add(block->phis()->at(j), zone()); |
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} |
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} while (need_another_iteration); |
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} |
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// Iteratively reduce all phis in the list. |
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ProcessPhis(&all_phis); |
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#if DEBUG |
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// Make sure that we *really* removed all redundant phis. |
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#endif |
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} |
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void HRedundantPhiEliminationPhase::ProcessBlock(HBasicBlock* block) {
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ProcessPhis(block->phis()); |
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} |
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void HRedundantPhiEliminationPhase::ProcessPhis(const ZoneList<HPhi*>* phis) {
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bool updated; |
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do {
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// Iterately replace all redundant phis in the given list. |
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updated = false; |
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for (int i = 0; i < phis->length(); i++) {
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HPhi* phi = phis->at(i); |
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if (phi->CheckFlag(HValue::kIsDead)) continue; // Already replaced. |
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HValue* replacement = phi->GetRedundantReplacement(); |
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if (replacement != NULL) {
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phi->SetFlag(HValue::kIsDead); |
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for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
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HValue* value = it.value(); |
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value->SetOperandAt(it.index(), replacement); |
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// Iterate again if used in another non-dead phi. |
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updated |= value->IsPhi() && !value->CheckFlag(HValue::kIsDead); |
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} |
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phi->block()->RemovePhi(phi); |
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} |
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} |
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} while (updated); |
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} |
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} } // namespace v8::internal |
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