WebKit/Source/JavaScriptCore/b3/air/AirEliminateDeadCode.cpp at main · WebKit/WebKit · GitHub

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* 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)

WebKit/Source/JavaScriptCore/b3/air/AirEliminateDeadCode.cpp at main · WebKit/WebKit · GitHub

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