/// Shrink the segments in the live interval for a given register to the last
/// use before each subsequent def. Unlike LiveIntervals::shrinkToUses, this
/// function will not mark any definitions of Reg as dead. The reason for this
/// is that this function is used while a MUX instruction is being expanded,
/// or while a conditional copy is undergoing predication. During these
/// processes, there may be defs present in the instruction sequence that have
/// not yet been removed, or there may be missing uses that have not yet been
/// added. We want to utilize LiveIntervals::shrinkToUses as much as possible,
/// but since it does not extend any intervals that are too short, we need to
/// pre-emptively extend them here in anticipation of further changes.
void HexagonExpandCondsets::shrinkToUses(unsigned Reg, LiveInterval &LI) {
SmallVector<MachineInstr*,4> Deads;
LIS->shrinkToUses(&LI, &Deads);
// Need to undo the deadification made by "shrinkToUses". It's easier to
// do it here, since we have a list of all instructions that were just
// marked as dead.
for (unsigned i = 0, n = Deads.size(); i < n; ++i) {
MachineInstr *MI = Deads[i];
// Clear the "dead" flag.
for (auto &Op : MI->operands()) {
if (!Op.isReg() || !Op.isDef() || Op.getReg() != Reg)
continue;
Op.setIsDead(false);
}
// Extend the live segment to the beginning of the next one.
LiveInterval::iterator End = LI.end();
SlotIndex S = LIS->getInstructionIndex(*MI).getRegSlot();
LiveInterval::iterator T = LI.FindSegmentContaining(S);
assert(T != End);
LiveInterval::iterator N = std::next(T);
if (N != End)
T->end = N->start;
else
T->end = LIS->getMBBEndIdx(MI->getParent());
}
updateKillFlags(Reg, LI);
}
bool LiveIntervals::computeDeadValues(LiveInterval &LI,
SmallVectorImpl<MachineInstr*> *dead) {
bool PHIRemoved = false;
for (auto VNI : LI.valnos) {
if (VNI->isUnused())
continue;
SlotIndex Def = VNI->def;
LiveRange::iterator I = LI.FindSegmentContaining(Def);
assert(I != LI.end() && "Missing segment for VNI");
// Is the register live before? Otherwise we may have to add a read-undef
// flag for subregister defs.
if (MRI->tracksSubRegLiveness()) {
if ((I == LI.begin() || std::prev(I)->end < Def) && !VNI->isPHIDef()) {
MachineInstr *MI = getInstructionFromIndex(Def);
MI->addRegisterDefReadUndef(LI.reg);
}
}
if (I->end != Def.getDeadSlot())
continue;
if (VNI->isPHIDef()) {
// This is a dead PHI. Remove it.
VNI->markUnused();
LI.removeSegment(I);
DEBUG(dbgs() << "Dead PHI at " << Def << " may separate interval\n");
PHIRemoved = true;
} else {
// This is a dead def. Make sure the instruction knows.
MachineInstr *MI = getInstructionFromIndex(Def);
assert(MI && "No instruction defining live value");
MI->addRegisterDead(LI.reg, TRI);
if (dead && MI->allDefsAreDead()) {
DEBUG(dbgs() << "All defs dead: " << Def << '\t' << *MI);
dead->push_back(MI);
}
}
}
return PHIRemoved;
}