CSE2410 Fall 2014 Bounce

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#include "hydrogen-canonicalize.h"

#include "hydrogen-redundant-phi.h"

namespace v8 {

namespace internal {

void HCanonicalizePhase::Run() {

  const ZoneList<HBasicBlock*>* blocks(graph()->blocks());

  // Before removing no-op instructions, save their semantic value.

  // We must be careful not to set the flag unnecessarily, because GVN

  // cannot identify two instructions when their flag value differs.

  for (int i = 0; i < blocks->length(); ++i) {

    for (HInstructionIterator it(blocks->at(i)); !it.Done(); it.Advance()) {

      HInstruction* instr = it.Current();

      if (instr->IsArithmeticBinaryOperation()) {

        if (instr->representation().IsInteger32()) {

          if (instr->HasAtLeastOneUseWithFlagAndNoneWithout(

                  HInstruction::kTruncatingToInt32)) {

            instr->SetFlag(HInstruction::kAllUsesTruncatingToInt32);

          }

        } else if (instr->representation().IsSmi()) {

          if (instr->HasAtLeastOneUseWithFlagAndNoneWithout(

                  HInstruction::kTruncatingToSmi)) {

            instr->SetFlag(HInstruction::kAllUsesTruncatingToSmi);

          } else if (instr->HasAtLeastOneUseWithFlagAndNoneWithout(

                         HInstruction::kTruncatingToInt32)) {

            // Avoid redundant minus zero check

            instr->SetFlag(HInstruction::kAllUsesTruncatingToInt32);

          }

        }

      }

    }

  }

  // Perform actual Canonicalization pass.

  HRedundantPhiEliminationPhase redundant_phi_eliminator(graph());

  for (int i = 0; i < blocks->length(); ++i) {

    // Eliminate redundant phis in the block first; changes to their inputs

    // might have made them redundant, and eliminating them creates more

    // opportunities for constant folding and strength reduction.

    redundant_phi_eliminator.ProcessBlock(blocks->at(i));

    // Now canonicalize each instruction.

    for (HInstructionIterator it(blocks->at(i)); !it.Done(); it.Advance()) {

      HInstruction* instr = it.Current();

      HValue* value = instr->Canonicalize();

      if (value != instr) instr->DeleteAndReplaceWith(value);

    }

  }

}

} }  // namespace v8::internal