void eliminateDeadCode(Trace* trace, IRFactory* irFactory) {
IRInstruction::List wl; // worklist of live instructions
Trace::List& exitTraces = trace->getExitTraces();
// first mark all exit traces as unreachable by setting the id on
// their labels to 0
for (Trace::Iterator it = exitTraces.begin();
it != exitTraces.end();
it++) {
Trace* trace = *it;
trace->getLabel()->setId(DEAD);
}
// mark the essential instructions and add them to the initial
// work list; also mark the exit traces that are reachable by
// any control flow instruction in the main trace.
initInstructions(trace, wl);
for (Trace::Iterator it = exitTraces.begin();
it != exitTraces.end();
it++) {
// only process those exit traces that are reachable from
// the main trace
Trace* trace = *it;
if (trace->getLabel()->getId() != DEAD) {
initInstructions(trace, wl);
}
}
// process the worklist
while (!wl.empty()) {
IRInstruction* inst = wl.front();
wl.pop_front();
for (uint32 i = 0; i < inst->getNumSrcs(); i++) {
SSATmp* src = inst->getSrc(i);
if (src->getInstruction()->isDefConst()) {
continue;
}
IRInstruction* srcInst = src->getInstruction();
if (srcInst->getId() == DEAD) {
srcInst->setId(LIVE);
wl.push_back(srcInst);
}
// <inst> consumes <srcInst> which is an IncRef,
// so we mark <srcInst> as REFCOUNT_CONSUMED.
if (inst->consumesReference(i) && srcInst->getOpcode() == IncRef) {
if (inst->getParent()->isMain() || !srcInst->getParent()->isMain()) {
// <srcInst> is consumed from its own trace.
srcInst->setId(REFCOUNT_CONSUMED);
} else {
// <srcInst> is consumed off trace.
if (srcInst->getId() != REFCOUNT_CONSUMED) {
// mark <srcInst> as REFCOUNT_CONSUMED_OFF_TRACE unless it is
// also consumed from its own trace.
srcInst->setId(REFCOUNT_CONSUMED_OFF_TRACE);
}
}
}
}
}
// Optimize IncRefs and DecRefs.
optimizeRefCount(trace);
for (Trace::Iterator it = exitTraces.begin(); it != exitTraces.end(); ++it) {
optimizeRefCount(*it);
}
if (RuntimeOption::EvalHHIREnableSinking) {
// Sink IncRefs consumed off trace.
IRInstruction::List toSink;
sinkIncRefs(trace, irFactory, toSink);
}
// now remove instructions whose id == DEAD
removeDeadInstructions(trace);
for (Trace::Iterator it = exitTraces.begin(); it != exitTraces.end(); it++) {
removeDeadInstructions(*it);
}
// If main trace ends with an unconditional jump, copy the target of
// the jump to the end of the trace
IRInstruction::List& instList = trace->getInstructionList();
IRInstruction::Iterator lastInst = instList.end();
lastInst--; // go back to the last instruction
IRInstruction* jmpInst = *lastInst;
if (jmpInst->getOpcode() == Jmp_) {
Trace* targetTrace = jmpInst->getLabel()->getTrace();
IRInstruction::List& targetInstList = targetTrace->getInstructionList();
IRInstruction::Iterator instIter = targetInstList.begin();
instIter++; // skip over label
// update the parent trace of the moved instructions
for (IRInstruction::Iterator it = instIter;
it != targetInstList.end();
++it) {
(*it)->setParent(trace);
}
instList.splice(lastInst, targetInstList, instIter, targetInstList.end());
// delete the jump instruction
instList.erase(lastInst);
}
// If main trace ends with a conditional jump with no side-effects on exit,
// hook it to the exitTrace and make it a TraceExitType::NormalCc
if (RuntimeOption::EvalHHIRDirectExit) {
IRInstruction::List& instList = trace->getInstructionList();
IRInstruction::Iterator tail = instList.end();
IRInstruction* jccInst = NULL;
IRInstruction* exitInst = NULL;
IRInstruction* exitCcInst = NULL;
Opcode opc = OpAdd;
// Normally Jcc comes before a Marker
for (int idx = 3; idx >= 0; idx--) {
tail--; // go back to the previous instruction
IRInstruction* inst = *tail;
opc = inst->getOpcode();
if (opc == ExitTrace) {
exitInst = *tail;
continue;
}
if (opc == Marker) {
continue;
}
if (jccCanBeDirectExit(opc)) {
jccInst = inst;
break;
}
break;
}
if (jccCanBeDirectExit(opc)) {
SSATmp* dst = jccInst->getDst();
Trace* targetTrace = jccInst->getLabel()->getTrace();
IRInstruction::List& targetInstList = targetTrace->getInstructionList();
IRInstruction::Iterator targetInstIter = targetInstList.begin();
targetInstIter++; // skip over label
// Check for a NormalCc exit with no side effects
for (IRInstruction::Iterator it = targetInstIter;
it != targetInstList.end();
++it) {
IRInstruction* instr = (*it);
// Extend to support ExitSlow, ExitSlowNoProgress, ...
Opcode opc = instr->getOpcode();
if (opc == ExitTraceCc) {
exitCcInst = instr;
break;
} else if (opc == Marker) {
continue;
} else {
// Do not optimize if there are other instructions
break;
}
}
if (exitInst && exitCcInst &&
exitCcInst->getNumSrcs() > NUM_FIXED_SRCS &&
exitInst->getNumSrcs() > NUM_FIXED_SRCS) {
// Found both exits, link them to Jcc for codegen
ASSERT(dst);
ExtendedInstruction* exCcInst = (ExtendedInstruction*)exitCcInst;
exCcInst->appendExtendedSrc(*irFactory, dst);
ExtendedInstruction* exInst = (ExtendedInstruction*)exitInst;
exInst->appendExtendedSrc(*irFactory, dst);
// Set flag so Jcc and exits know this is active
dst->setTCA(kIRDirectJccJmpActive);
}
}
}
// If main trace starts with guards, have them generate a patchable jump
// to the anchor trace
if (RuntimeOption::EvalHHIRDirectExit) {
LabelInstruction* guardLabel = NULL;
IRInstruction::List& instList = trace->getInstructionList();
// Check the beginning of the trace for guards
for (IRInstruction::Iterator it = instList.begin(); it != instList.end();
++it) {
IRInstruction* inst = *it;
Opcode opc = inst->getOpcode();
if (inst->getLabel() &&
(opc == LdLoc || opc == LdStack ||
opc == GuardLoc || opc == GuardStk)) {
LabelInstruction* exitLabel = inst->getLabel();
// Find the GuardFailure's label and confirm this branches there
if (guardLabel == NULL) {
Trace* exitTrace = exitLabel->getTrace();
IRInstruction::List& xList = exitTrace->getInstructionList();
IRInstruction::Iterator instIter = xList.begin();
instIter++; // skip over label
// Confirm this is a GuardExit
for (IRInstruction::Iterator it = instIter; it != xList.end(); ++it) {
IRInstruction* i = *it;
Opcode op = i->getOpcode();
if (op == Marker) {
continue;
}
if (op == ExitGuardFailure) {
guardLabel = exitLabel;
}
// Do not optimize if other instructions are on exit trace
break;
}
}
if (exitLabel == guardLabel) {
inst->setTCA(kIRDirectGuardActive);
continue;
}
break;
}
if (opc == Marker || opc == DefLabel || opc == DefSP || opc == DefFP ||
opc == LdStack) {
continue;
}
break;
}
}
}
void eliminateDeadCode(Trace* trace, IRFactory* irFactory) {
IRInstruction::List wl; // worklist of live instructions
Trace::List& exitTraces = trace->getExitTraces();
// first mark all exit traces as unreachable by setting the id on
// their labels to 0
for (Trace::Iterator it = exitTraces.begin();
it != exitTraces.end();
it++) {
Trace* trace = *it;
trace->getLabel()->setId(DEAD);
}
// mark the essential instructions and add them to the initial
// work list; also mark the exit traces that are reachable by
// any control flow instruction in the main trace.
initInstructions(trace, wl);
for (Trace::Iterator it = exitTraces.begin();
it != exitTraces.end();
it++) {
// only process those exit traces that are reachable from
// the main trace
Trace* trace = *it;
if (trace->getLabel()->getId() != DEAD) {
initInstructions(trace, wl);
}
}
// process the worklist
while (!wl.empty()) {
IRInstruction* inst = wl.front();
wl.pop_front();
for (uint32 i = 0; i < inst->getNumSrcs(); i++) {
SSATmp* src = inst->getSrc(i);
if (src->getInstruction()->isDefConst()) {
continue;
}
IRInstruction* srcInst = src->getInstruction();
if (srcInst->getId() == DEAD) {
srcInst->setId(LIVE);
wl.push_back(srcInst);
}
// <inst> consumes <srcInst> which is an IncRef,
// so we mark <srcInst> as REFCOUNT_CONSUMED.
if (inst->consumesReference(i) && srcInst->getOpcode() == IncRef) {
if (inst->getParent()->isMain() || !srcInst->getParent()->isMain()) {
// <srcInst> is consumed from its own trace.
srcInst->setId(REFCOUNT_CONSUMED);
} else {
// <srcInst> is consumed off trace.
if (srcInst->getId() != REFCOUNT_CONSUMED) {
// mark <srcInst> as REFCOUNT_CONSUMED_OFF_TRACE unless it is
// also consumed from its own trace.
srcInst->setId(REFCOUNT_CONSUMED_OFF_TRACE);
}
}
}
}
}
// Optimize IncRefs and DecRefs.
optimizeRefCount(trace);
for (Trace::Iterator it = exitTraces.begin(); it != exitTraces.end(); ++it) {
optimizeRefCount(*it);
}
if (RuntimeOption::EvalHHIREnableSinking) {
// Sink IncRefs consumed off trace.
IRInstruction::List toSink;
sinkIncRefs(trace, irFactory, toSink);
}
// now remove instructions whose id == DEAD
removeDeadInstructions(trace);
for (Trace::Iterator it = exitTraces.begin(); it != exitTraces.end(); it++) {
removeDeadInstructions(*it);
}
}
// Sink IncRefs consumed off trace.
// When <trace> is an exit trace, <toSink> contains all live IncRefs in the
// main trace that are consumed off trace.
void sinkIncRefs(Trace* trace,
IRFactory* irFactory,
IRInstruction::List& toSink) {
IRInstruction::List& instList = trace->getInstructionList();
IRInstruction::Iterator it;
std::map<SSATmp*, SSATmp*> sunkTmps;
if (!trace->isMain()) {
// Sink REFCOUNT_CONSUMED_OFF_TRACE IncRefs before the first non-label
// instruction, and create a mapping between the original tmps to the sunk
// tmps so that we can later replace the original ones with the sunk ones.
for (IRInstruction::ReverseIterator j = toSink.rbegin();
j != toSink.rend();
++j) {
// prependInstruction inserts an instruction to the beginning. Therefore,
// we iterate through toSink in the reversed order.
IRInstruction* sunkInst = irFactory->incRef((*j)->getSrc(0));
sunkInst->setId(LIVE);
trace->prependInstruction(sunkInst);
ASSERT((*j)->getDst());
ASSERT(!sunkTmps.count((*j)->getDst()));
sunkTmps[(*j)->getDst()] = irFactory->getSSATmp(sunkInst);
}
}
// An exit trace may be entered from multiple exit points. We keep track of
// which exit traces we already pushed sunk IncRefs to, so that we won't push
// them multiple times.
std::set<Trace*> pushedTo;
for (it = instList.begin(); it != instList.end(); ++it) {
IRInstruction* inst = *it;
if (trace->isMain()) {
if (inst->getOpcode() == IncRef) {
// Must be REFCOUNT_CONSUMED or REFCOUNT_CONSUMED_OFF_TRACE;
// otherwise, it should be already removed in optimizeRefCount.
ASSERT(inst->getId() == REFCOUNT_CONSUMED ||
inst->getId() == REFCOUNT_CONSUMED_OFF_TRACE);
if (inst->getId() == REFCOUNT_CONSUMED_OFF_TRACE) {
inst->setOpcode(Mov);
// Mark them as dead so that they'll be removed later.
inst->setId(DEAD);
// Put all REFCOUNT_CONSUMED_OFF_TRACE IncRefs to the sinking list.
toSink.push_back(inst);
}
}
if (inst->getOpcode() == DecRefNZ) {
IRInstruction* srcInst = inst->getSrc(0)->getInstruction();
if (srcInst->getId() == DEAD) {
inst->setId(DEAD);
// This may take O(I) time where I is the number of IncRefs
// in the main trace.
toSink.remove(srcInst);
}
}
if (LabelInstruction* label = inst->getLabel()) {
Trace* exitTrace = label->getTrace();
if (!pushedTo.count(exitTrace)) {
pushedTo.insert(exitTrace);
sinkIncRefs(exitTrace, irFactory, toSink);
}
}
} else {
// Replace the original tmps with the sunk tmps.
for (uint32 i = 0; i < inst->getNumSrcs(); ++i) {
SSATmp* src = inst->getSrc(i);
if (SSATmp* sunkTmp = sunkTmps[src]) {
inst->setSrc(i, sunkTmp);
}
}
}
}
// Do copyProp at last, because we need to keep REFCOUNT_CONSUMED_OFF_TRACE
// Movs as the prototypes for sunk instructions.
for (it = instList.begin(); it != instList.end(); ++it) {
Simplifier::copyProp(*it);
}
}
void eliminateDeadCode(Trace* trace, IRFactory* irFactory) {
auto removeEmptyExitTraces = [&] {
trace->getExitTraces().remove_if([](Trace* exit) {
return exit->getBlocks().empty();
});
};
// kill unreachable code and remove any traces that are now empty
BlockList blocks = removeUnreachable(trace, irFactory);
removeEmptyExitTraces();
// mark the essential instructions and add them to the initial
// work list; this will also mark reachable exit traces. All
// other instructions marked dead.
DceState state(irFactory, DceFlags());
WorkList wl = initInstructions(trace, blocks, state, irFactory);
// process the worklist
while (!wl.empty()) {
auto* inst = wl.front();
wl.pop_front();
for (uint32_t i = 0; i < inst->getNumSrcs(); i++) {
SSATmp* src = inst->getSrc(i);
if (src->getInstruction()->getOpcode() == DefConst) {
continue;
}
IRInstruction* srcInst = src->getInstruction();
if (state[srcInst].isDead()) {
state[srcInst].setLive();
wl.push_back(srcInst);
}
// <inst> consumes <srcInst> which is an IncRef, so we mark <srcInst> as
// REFCOUNT_CONSUMED. If the source instruction is a GuardType and guards
// to a maybeCounted type, we need to trace through to the source for
// refcounting purposes.
while (srcInst->getOpcode() == GuardType &&
srcInst->getTypeParam().maybeCounted()) {
srcInst = srcInst->getSrc(0)->getInstruction();
}
if (inst->consumesReference(i) && srcInst->getOpcode() == IncRef) {
if (inst->getTrace()->isMain() || !srcInst->getTrace()->isMain()) {
// <srcInst> is consumed from its own trace.
state[srcInst].setCountConsumed();
} else {
// <srcInst> is consumed off trace.
if (!state[srcInst].countConsumed()) {
// mark <srcInst> as REFCOUNT_CONSUMED_OFF_TRACE unless it is
// also consumed from its own trace.
state[srcInst].setCountConsumedOffTrace();
}
}
}
}
}
// Optimize IncRefs and DecRefs.
forEachTrace(trace, [&](Trace* t) { optimizeRefCount(t, state); });
if (RuntimeOption::EvalHHIREnableSinking) {
// Sink IncRefs consumed off trace.
sinkIncRefs(trace, irFactory, state);
}
// now remove instructions whose id == DEAD
removeDeadInstructions(trace, state);
for (Trace* exit : trace->getExitTraces()) {
removeDeadInstructions(exit, state);
}
// and remove empty exit traces
removeEmptyExitTraces();
}