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Reduce queue size in dead code elimination by eagerly processing live instructions.

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BUG=
R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/27178002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17196 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
titzer@chromium.org 2013-10-14 13:32:02 +00:00
parent 9fadd29544
commit 63305af0f8
2 changed files with 37 additions and 32 deletions
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66
src/hydrogen-dce.cc
View File

@ -31,56 +31,60 @@
namespace v8 {
namespace internal {
bool HDeadCodeEliminationPhase::MarkLive(HValue* ref, HValue* instr) {
if (instr->CheckFlag(HValue::kIsLive)) return false;
instr->SetFlag(HValue::kIsLive);
void HDeadCodeEliminationPhase::MarkLive(
HValue* instr, ZoneList<HValue*>* worklist) {
if (instr->CheckFlag(HValue::kIsLive)) return; // Already live.
if (FLAG_trace_dead_code_elimination) {
HeapStringAllocator allocator;
StringStream stream(&allocator);
if (ref != NULL) {
ref->PrintTo(&stream);
} else {
stream.Add("root ");
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);
}
}
stream.Add(" -> ");
instr->PrintTo(&stream);
PrintF("[MarkLive %s]\n", *stream.ToCString());
}
}
return true;
void HDeadCodeEliminationPhase::PrintLive(HValue* ref, HValue* instr) {
HeapStringAllocator allocator;
StringStream stream(&allocator);
if (ref != NULL) {
ref->PrintTo(&stream);
} else {
stream.Add("root ");
}
stream.Add(" -> ");
instr->PrintTo(&stream);
PrintF("[MarkLive %s]\n", *stream.ToCString());
}
void HDeadCodeEliminationPhase::MarkLiveInstructions() {
ZoneList<HValue*> worklist(graph()->blocks()->length(), zone());
ZoneList<HValue*> worklist(10, zone());
// Mark initial root instructions for dead code elimination.
// 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(NULL, instr)) {
worklist.Add(instr, zone());
}
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(NULL, phi)) {
worklist.Add(phi, zone());
}
if (phi->CannotBeEliminated()) MarkLive(phi, &worklist);
}
}
// Transitively mark all inputs of live instructions live.
while (!worklist.is_empty()) {
HValue* instr = worklist.RemoveLast();
for (int i = 0; i < instr->OperandCount(); ++i) {
if (MarkLive(instr, instr->OperandAt(i))) {
worklist.Add(instr->OperandAt(i), zone());
}
}
}
ASSERT(worklist.is_empty()); // Should have processed everything.
}

3
src/hydrogen-dce.h
View File

@ -45,7 +45,8 @@ class HDeadCodeEliminationPhase : public HPhase {
}
private:
bool MarkLive(HValue* ref, HValue* instr);
void MarkLive(HValue* instr, ZoneList<HValue*>* worklist);
void PrintLive(HValue* ref, HValue* instr);
void MarkLiveInstructions();
void RemoveDeadInstructions();
};