v8::internal::HDeadCodeEliminationPhase Class Reference

#include <hydrogen-dce.h>

Inheritance diagram for v8::internal::HDeadCodeEliminationPhase:

Collaboration diagram for v8::internal::HDeadCodeEliminationPhase:

Public Member Functions
	HDeadCodeEliminationPhase (HGraph *graph)
void	Run ()
Public Member Functions inherited from v8::internal::HPhase
	HPhase (const char *name, HGraph *graph)
	~HPhase ()

Private Member Functions
void	MarkLive (HValue *instr, ZoneList< HValue * > *worklist)
void	PrintLive (HValue *ref, HValue *instr)
void	MarkLiveInstructions ()
void	RemoveDeadInstructions ()

Additional Inherited Members
Protected Member Functions inherited from v8::internal::HPhase
HGraph *	graph () const

Detailed Description

Definition at line 14 of file hydrogen-dce.h.

Constructor & Destructor Documentation

HDeadCodeEliminationPhase()

v8::internal::HDeadCodeEliminationPhase::HDeadCodeEliminationPhase ( HGraph *  graph )

inlineexplicit

Definition at line 16 of file hydrogen-dce.h.

      : HPhase("H_Dead code elimination", graph) { }

Member Function Documentation

MarkLive()

void v8::internal::HDeadCodeEliminationPhase::MarkLive ( HValue *  instr, ZoneList< HValue * > *  worklist  )

private

Definition at line 11 of file hydrogen-dce.cc.

                                                {
  if (instr->CheckFlag(HValue::kIsLive)) return;  // Already live.
 
  if (FLAG_trace_dead_code_elimination) PrintLive(NULL, instr);
 
  // Transitively mark all inputs of live instructions live.
  worklist->Add(instr, zone());
  while (!worklist->is_empty()) {
    HValue* instr = worklist->RemoveLast();
    instr->SetFlag(HValue::kIsLive);
    for (int i = 0; i < instr->OperandCount(); ++i) {
      HValue* input = instr->OperandAt(i);
      if (!input->CheckFlag(HValue::kIsLive)) {
        input->SetFlag(HValue::kIsLive);
        worklist->Add(input, zone());
        if (FLAG_trace_dead_code_elimination) PrintLive(instr, input);
      }
    }
  }
}

References v8::internal::List< T, AllocationPolicy >::Add(), v8::internal::HValue::CheckFlag(), v8::internal::HValue::kIsLive, NULL, v8::internal::HValue::OperandAt(), v8::internal::HValue::OperandCount(), PrintLive(), and v8::internal::HValue::SetFlag().

Referenced by MarkLiveInstructions().

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MarkLiveInstructions()

void v8::internal::HDeadCodeEliminationPhase::MarkLiveInstructions ( )

private

Definition at line 46 of file hydrogen-dce.cc.

                                                     {
  ZoneList<HValue*> worklist(10, zone());
 
  // Transitively mark all live instructions, starting from roots.
  for (int i = 0; i < graph()->blocks()->length(); ++i) {
    HBasicBlock* block = graph()->blocks()->at(i);
    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
      HInstruction* instr = it.Current();
      if (instr->CannotBeEliminated()) MarkLive(instr, &worklist);
    }
    for (int j = 0; j < block->phis()->length(); j++) {
      HPhi* phi = block->phis()->at(j);
      if (phi->CannotBeEliminated()) MarkLive(phi, &worklist);
    }
  }
 
  DCHECK(worklist.is_empty());  // Should have processed everything.
}

References v8::internal::HValue::CannotBeEliminated(), DCHECK, v8::internal::HPhase::graph(), and MarkLive().

Referenced by Run().

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PrintLive()

void v8::internal::HDeadCodeEliminationPhase::PrintLive ( HValue *  ref, HValue *  instr  )

private

Definition at line 34 of file hydrogen-dce.cc.

                                                                    {
  OFStream os(stdout);
  os << "[MarkLive ";
  if (ref != NULL) {
    os << *ref;
  } else {
    os << "root ";
  }
  os << " -> " << *instr << "]" << endl;
}

References v8::internal::endl(), and NULL.

Referenced by MarkLive().

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RemoveDeadInstructions()

void v8::internal::HDeadCodeEliminationPhase::RemoveDeadInstructions ( )

private

Definition at line 66 of file hydrogen-dce.cc.

                                                       {
  ZoneList<HPhi*> worklist(graph()->blocks()->length(), zone());
 
  // Remove any instruction not marked kIsLive.
  for (int i = 0; i < graph()->blocks()->length(); ++i) {
    HBasicBlock* block = graph()->blocks()->at(i);
    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
      HInstruction* instr = it.Current();
      if (!instr->CheckFlag(HValue::kIsLive)) {
        // Instruction has not been marked live, so remove it.
        instr->DeleteAndReplaceWith(NULL);
      } else {
        // Clear the liveness flag to leave the graph clean for the next DCE.
        instr->ClearFlag(HValue::kIsLive);
      }
    }
    // Collect phis that are dead and remove them in the next pass.
    for (int j = 0; j < block->phis()->length(); j++) {
      HPhi* phi = block->phis()->at(j);
      if (!phi->CheckFlag(HValue::kIsLive)) {
        worklist.Add(phi, zone());
      } else {
        phi->ClearFlag(HValue::kIsLive);
      }
    }
  }
 
  // Process phis separately to avoid simultaneously mutating the phi list.
  while (!worklist.is_empty()) {
    HPhi* phi = worklist.RemoveLast();
    HBasicBlock* block = phi->block();
    phi->DeleteAndReplaceWith(NULL);
    if (phi->HasMergedIndex()) {
      block->RecordDeletedPhi(phi->merged_index());
    }
  }
}

References v8::internal::List< T, AllocationPolicy >::Add(), v8::internal::HValue::CheckFlag(), v8::internal::HValue::ClearFlag(), v8::internal::HValue::DeleteAndReplaceWith(), v8::internal::HPhase::graph(), v8::internal::HValue::kIsLive, and NULL.

Referenced by Run().

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Run()

void v8::internal::HDeadCodeEliminationPhase::Run ( )

inline

Definition at line 19 of file hydrogen-dce.h.

             {
    MarkLiveInstructions();
    RemoveDeadInstructions();
  }

References MarkLiveInstructions(), and RemoveDeadInstructions().

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The documentation for this class was generated from the following files:

• /mnt/V8SourceCode/src/hydrogen-dce.h
• /mnt/V8SourceCode/src/hydrogen-dce.cc