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      1 // Copyright 2013 the V8 project authors. All rights reserved.
      2 // Redistribution and use in source and binary forms, with or without
      3 // modification, are permitted provided that the following conditions are
      4 // met:
      5 //
      6 //     * Redistributions of source code must retain the above copyright
      7 //       notice, this list of conditions and the following disclaimer.
      8 //     * Redistributions in binary form must reproduce the above
      9 //       copyright notice, this list of conditions and the following
     10 //       disclaimer in the documentation and/or other materials provided
     11 //       with the distribution.
     12 //     * Neither the name of Google Inc. nor the names of its
     13 //       contributors may be used to endorse or promote products derived
     14 //       from this software without specific prior written permission.
     15 //
     16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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     26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27 
     28 #include "hydrogen-redundant-phi.h"
     29 
     30 namespace v8 {
     31 namespace internal {
     32 
     33 void HRedundantPhiEliminationPhase::Run() {
     34   // Gather all phis from all blocks first.
     35   const ZoneList<HBasicBlock*>* blocks(graph()->blocks());
     36   ZoneList<HPhi*> all_phis(blocks->length(), zone());
     37   for (int i = 0; i < blocks->length(); ++i) {
     38     HBasicBlock* block = blocks->at(i);
     39     for (int j = 0; j < block->phis()->length(); j++) {
     40       all_phis.Add(block->phis()->at(j), zone());
     41     }
     42   }
     43 
     44   // Iteratively reduce all phis in the list.
     45   ProcessPhis(&all_phis);
     46 
     47 #if DEBUG
     48   // Make sure that we *really* removed all redundant phis.
     49   for (int i = 0; i < blocks->length(); ++i) {
     50     for (int j = 0; j < blocks->at(i)->phis()->length(); j++) {
     51       ASSERT(blocks->at(i)->phis()->at(j)->GetRedundantReplacement() == NULL);
     52     }
     53   }
     54 #endif
     55 }
     56 
     57 
     58 void HRedundantPhiEliminationPhase::ProcessBlock(HBasicBlock* block) {
     59   ProcessPhis(block->phis());
     60 }
     61 
     62 
     63 void HRedundantPhiEliminationPhase::ProcessPhis(const ZoneList<HPhi*>* phis) {
     64   bool updated;
     65   do {
     66     // Iterately replace all redundant phis in the given list.
     67     updated = false;
     68     for (int i = 0; i < phis->length(); i++) {
     69       HPhi* phi = phis->at(i);
     70       if (phi->CheckFlag(HValue::kIsDead)) continue;  // Already replaced.
     71 
     72       HValue* replacement = phi->GetRedundantReplacement();
     73       if (replacement != NULL) {
     74         phi->SetFlag(HValue::kIsDead);
     75         for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
     76           HValue* value = it.value();
     77           value->SetOperandAt(it.index(), replacement);
     78           // Iterate again if used in another non-dead phi.
     79           updated |= value->IsPhi() && !value->CheckFlag(HValue::kIsDead);
     80         }
     81         phi->block()->RemovePhi(phi);
     82       }
     83     }
     84   } while (updated);
     85 }
     86 
     87 
     88 } }  // namespace v8::internal
     89