Simplify redundant phi elimination and use during canonicalization too.
BUG= R=verwaest@chromium.org Review URL: https://codereview.chromium.org/25896006 git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17124 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
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@ -26,6 +26,7 @@
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "hydrogen-canonicalize.h"
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#include "hydrogen-redundant-phi.h"
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namespace v8 {
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namespace internal {
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@ -57,8 +58,15 @@ void HCanonicalizePhase::Run() {
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}
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}
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}
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// Perform actual Canonicalization pass.
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HRedundantPhiEliminationPhase redundant_phi_eliminator(graph());
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for (int i = 0; i < blocks->length(); ++i) {
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// Eliminate redundant phis in the block first; changes to their inputs
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// might have made them redundant, and eliminating them creates more
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// opportunities for constant folding and strength reduction.
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redundant_phi_eliminator.ProcessBlock(blocks->at(i));
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// Now canonicalize each instruction.
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for (HInstructionIterator it(blocks->at(i)); !it.Done(); it.Advance()) {
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HInstruction* instr = it.Current();
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HValue* value = instr->Canonicalize();
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@ -31,37 +31,18 @@ namespace v8 {
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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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@ -73,4 +54,35 @@ void HRedundantPhiEliminationPhase::Run() {
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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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@ -42,8 +42,11 @@ class HRedundantPhiEliminationPhase : public HPhase {
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: HPhase("H_Redundant phi elimination", graph) { }
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void Run();
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void ProcessBlock(HBasicBlock* block);
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private:
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void ProcessPhis(const ZoneList<HPhi*>* phis);
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DISALLOW_COPY_AND_ASSIGN(HRedundantPhiEliminationPhase);
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};
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