void LiveRangeCalc::calculate(LiveInterval &LI, bool TrackSubRegs) {
assert(MRI && Indexes && "call reset() first");
// Step 1: Create minimal live segments for every definition of Reg.
// Visit all def operands. If the same instruction has multiple defs of Reg,
// createDeadDef() will deduplicate.
const TargetRegisterInfo &TRI = *MRI->getTargetRegisterInfo();
unsigned Reg = LI.reg;
for (const MachineOperand &MO : MRI->reg_nodbg_operands(Reg)) {
if (!MO.isDef() && !MO.readsReg())
continue;
unsigned SubReg = MO.getSubReg();
if (LI.hasSubRanges() || (SubReg != 0 && TrackSubRegs)) {
LaneBitmask Mask = SubReg != 0 ? TRI.getSubRegIndexLaneMask(SubReg)
: MRI->getMaxLaneMaskForVReg(Reg);
// If this is the first time we see a subregister def, initialize
// subranges by creating a copy of the main range.
if (!LI.hasSubRanges() && !LI.empty()) {
LaneBitmask ClassMask = MRI->getMaxLaneMaskForVReg(Reg);
LI.createSubRangeFrom(*Alloc, ClassMask, LI);
}
for (LiveInterval::SubRange &S : LI.subranges()) {
// A Mask for subregs common to the existing subrange and current def.
LaneBitmask Common = S.LaneMask & Mask;
if (Common == 0)
continue;
// A Mask for subregs covered by the subrange but not the current def.
LaneBitmask LRest = S.LaneMask & ~Mask;
LiveInterval::SubRange *CommonRange;
if (LRest != 0) {
// Split current subrange into Common and LRest ranges.
S.LaneMask = LRest;
CommonRange = LI.createSubRangeFrom(*Alloc, Common, S);
} else {
assert(Common == S.LaneMask);
CommonRange = &S;
}
if (MO.isDef())
createDeadDef(*Indexes, *Alloc, *CommonRange, MO);
Mask &= ~Common;
}
// Create a new SubRange for subregs we did not cover yet.
if (Mask != 0) {
LiveInterval::SubRange *NewRange = LI.createSubRange(*Alloc, Mask);
if (MO.isDef())
createDeadDef(*Indexes, *Alloc, *NewRange, MO);
}
}
// Create the def in the main liverange. We do not have to do this if
// subranges are tracked as we recreate the main range later in this case.
if (MO.isDef() && !LI.hasSubRanges())
createDeadDef(*Indexes, *Alloc, LI, MO);
}
// We may have created empty live ranges for partially undefined uses, we
// can't keep them because we won't find defs in them later.
LI.removeEmptySubRanges();
// Step 2: Extend live segments to all uses, constructing SSA form as
// necessary.
if (LI.hasSubRanges()) {
for (LiveInterval::SubRange &S : LI.subranges()) {
resetLiveOutMap();
extendToUses(S, Reg, S.LaneMask);
}
LI.clear();
constructMainRangeFromSubranges(LI);
} else {
resetLiveOutMap();
extendToUses(LI, Reg, ~0u);
}
}
