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/*
* Copyright (C) 2015-2016 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 "B3IndexSet.h"
namespace JSC { namespace B3 { namespace Air {
bool eliminateDeadCode(Code& code)
{
PhaseScope phaseScope(code, "eliminateDeadCode");
HashSet<Tmp> liveTmps;
IndexSet<StackSlot> liveStackSlots;
bool changed;
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 addLiveArg = [&] (const Arg& arg) -> bool {
switch (arg.kind()) {
case Arg::Tmp:
if (arg.isReg())
return false;
return liveTmps.add(arg.tmp()).isNewEntry;
case Arg::Stack:
if (arg.stackSlot()->isLocked())
return false;
return liveStackSlots.add(arg.stackSlot());
default:
return false;
}
};
auto isInstLive = [&] (Inst& inst) -> bool {
if (inst.hasNonArgEffects())
return true;
// This instruction should be presumed dead, if its Args are all dead.
bool storesToLive = false;
inst.forEachArg(
[&] (Arg& arg, Arg::Role role, Arg::Type, Arg::Width) {
if (!Arg::isAnyDef(role))
return;
if (role == Arg::Scratch)
return;
storesToLive |= isArgLive(arg);
});
return storesToLive;
};
auto handleInst = [&] (Inst& inst) {
if (!isInstLive(inst))
return;
// We get here if the Inst is live. For simplicity we say that a live instruction forces
// liveness upon everything it mentions.
for (Arg& arg : inst.args) {
changed |= addLiveArg(arg);
arg.forEachTmpFast(
[&] (Tmp& tmp) {
changed |= addLiveArg(tmp);
});
}
};
auto runForward = [&] () -> bool {
changed = false;
for (BasicBlock* block : code) {
for (Inst& inst : *block)
handleInst(inst);
}
return changed;
};
auto runBackward = [&] () -> bool {
changed = false;
for (unsigned blockIndex = code.size(); blockIndex--;) {
BasicBlock* block = code[blockIndex];
for (unsigned instIndex = block->size(); instIndex--;)
handleInst(block->at(instIndex));
}
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;
}
unsigned removedInstCount = 0;
for (BasicBlock* block : code) {
removedInstCount += block->insts().removeAllMatching(
[&] (Inst& inst) -> bool {
return !isInstLive(inst);
});
}
return !!removedInstCount;
}
} } } // namespace JSC::B3::Air
#endif // ENABLE(B3_JIT)
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