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Copy pathAirEliminateDeadCode.cpp
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176 lines (151 loc) · 5.79 KB
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/*
* Copyright (C) 2015-2017 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "AirEliminateDeadCode.h"
#if ENABLE(B3_JIT)
#include "AirCode.h"
#include "AirInstInlines.h"
#include "AirPhaseScope.h"
#include "AirTmpInlines.h"
#include "AirTmpSet.h"
#include <wtf/IndexSet.h>
namespace JSC { namespace B3 { namespace Air {
bool eliminateDeadCode(Code& code)
{
PhaseScope phaseScope(code, "eliminateDeadCode"_s);
TmpSet liveTmps;
IndexSet<StackSlot*> liveStackSlots;
bool changed { false };
auto isArgLive = [&](const Arg& arg) -> bool {
switch (arg.kind()) {
case Arg::Tmp:
if (arg.isReg())
return true;
return liveTmps.contains(arg.tmp());
case Arg::Stack:
if (arg.stackSlot()->isLocked())
return true;
return liveStackSlots.contains(arg.stackSlot());
default:
return true;
}
};
auto isInstLiveByDefs = [&](Inst& inst) -> bool {
// This instruction should be presumed dead, if its Args are all dead.
bool storesToLive = false;
inst.forEachArg(
[&] (Arg& arg, Arg::Role role, Bank, Width) {
if (!Arg::isAnyDef(role))
return;
if (role == Arg::Scratch)
return;
storesToLive |= isArgLive(arg);
});
return storesToLive;
};
auto isInstLive = [&](Inst& inst) -> bool {
return inst.hasNonArgEffects() || isInstLiveByDefs(inst);
};
auto markArgsLive = [&](Inst& inst) {
for (Arg& arg : inst.args()) {
if (arg.isStack() && !arg.stackSlot()->isLocked())
changed |= liveStackSlots.add(arg.stackSlot());
arg.forEachTmpFast(
[&] (Tmp& tmp) {
if (!tmp.isReg())
changed |= liveTmps.add(tmp);
});
}
};
Vector<Inst*> backingStore;
for (unsigned blockIndex = code.size(); blockIndex--;) {
BasicBlock* block = code[blockIndex];
if (!block)
continue;
for (unsigned instIndex = block->size(); instIndex--;) {
Inst& inst = block->at(instIndex);
if (!isInstLive(inst))
backingStore.append(&inst);
else
markArgsLive(inst);
}
}
auto deadCandidatesInBackwardOrder = backingStore.mutableSpan();
// Inst in deadCandidatesInBackwardOrder already have hasNonArgEffects() == false, invariant
// under live-set growth, so the fixpoint skips that re-check.
auto handleInst = [&](Inst& inst) -> bool {
if (!isInstLiveByDefs(inst))
return false;
markArgsLive(inst);
return true;
};
auto runBackward = [&] -> bool {
changed = false;
auto [begin, end] = std::ranges::remove_if(deadCandidatesInBackwardOrder,
[&] (Inst* inst) -> bool {
bool result = handleInst(*inst);
changed |= result;
return result;
});
deadCandidatesInBackwardOrder = deadCandidatesInBackwardOrder.first(begin - deadCandidatesInBackwardOrder.begin());
return changed;
};
auto runForward = [&] -> bool {
changed = false;
auto [begin, end] = std::ranges::remove_if(deadCandidatesInBackwardOrder | std::views::reverse,
[&] (Inst* inst) -> bool {
bool result = handleInst(*inst);
changed |= result;
return result;
});
deadCandidatesInBackwardOrder = deadCandidatesInBackwardOrder.last(deadCandidatesInBackwardOrder.end() - begin.base());
return changed;
};
for (;;) {
// Propagating backward is most likely to be profitable.
if (!runBackward())
break;
if (!runBackward())
break;
// Occasionally propagating forward greatly reduces the likelihood of pathologies.
if (!runForward())
break;
}
// After the fixpoint, deadCandidatesInBackwardOrder holds exactly the dead Insts. Null them
// out and sweep with the cheap !inst predicate.
if (deadCandidatesInBackwardOrder.empty())
return false;
for (Inst* inst : deadCandidatesInBackwardOrder)
*inst = Inst();
for (BasicBlock* block : code) {
block->insts().removeAllMatching(
[&] (Inst& inst) -> bool {
return !inst;
});
}
return true;
}
} } } // namespace JSC::B3::Air
#endif // ENABLE(B3_JIT)