Reviewers: Dmitry Lomov (chromium),
Message:
Measured an 7x decrease in the memory allocated in the zone during this
phase,
from 2.2mb to 0.3mb on benchmarks/run.js. Shouldn't affect performance
significantly, and should generate identical code.
Description:
Reduce queue size in dead code elimination by eagerly processing live
instructions.
BUG=
Please review this at https://codereview.chromium.org/27178002/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files (+34, -31 lines):
M src/hydrogen-dce.h
M src/hydrogen-dce.cc
Index: src/hydrogen-dce.cc
diff --git a/src/hydrogen-dce.cc b/src/hydrogen-dce.cc
index
0e7253d5a4869d44ee137129bd4c037eb8774dfd..aa3804078a4142f73af292bdad0097cf3df11277
100644
--- a/src/hydrogen-dce.cc
+++ b/src/hydrogen-dce.cc
@@ -31,24 +31,40 @@
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());
}
@@ -60,25 +76,11 @@ void HDeadCodeEliminationPhase::MarkLiveInstructions() {
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());
- }
- }
- }
-
- // 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());
- }
+ if (phi->CannotBeEliminated()) MarkLive(phi, &worklist);
}
}
}
Index: src/hydrogen-dce.h
diff --git a/src/hydrogen-dce.h b/src/hydrogen-dce.h
index
19749f279a2e1cb632ba5a300033e5a9f038638f..2d73b380e40831147e5b5e586f0c805d9c45f877
100644
--- a/src/hydrogen-dce.h
+++ b/src/hydrogen-dce.h
@@ -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();
};
--
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