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[Coalescer] Move code added in #116191 #121779

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Jan 7, 2025
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[Coalescer] Move code added in #116191 #121779

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41 changes: 20 additions & 21 deletions llvm/lib/CodeGen/RegisterCoalescer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1374,27 +1374,6 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
MachineInstr &NewMI = *std::prev(MII);
NewMI.setDebugLoc(DL);

// In a situation like the following:
//
// undef %2.subreg:reg = INST %1:reg ; DefMI (rematerializable),
// ; DefSubIdx = subreg
// %3:reg = COPY %2 ; SrcIdx = DstIdx = 0
// .... = SOMEINSTR %3:reg
//
// there are no subranges for %3 so after rematerialization we need
// to explicitly create them. Undefined subranges are removed later on.
if (DstReg.isVirtual() && DefSubIdx && !CP.getSrcIdx() && !CP.getDstIdx() &&
MRI->shouldTrackSubRegLiveness(DstReg)) {
LiveInterval &DstInt = LIS->getInterval(DstReg);
if (!DstInt.hasSubRanges()) {
LaneBitmask FullMask = MRI->getMaxLaneMaskForVReg(DstReg);
LaneBitmask UsedLanes = TRI->getSubRegIndexLaneMask(DefSubIdx);
LaneBitmask UnusedLanes = FullMask & ~UsedLanes;
DstInt.createSubRangeFrom(LIS->getVNInfoAllocator(), UsedLanes, DstInt);
DstInt.createSubRangeFrom(LIS->getVNInfoAllocator(), UnusedLanes, DstInt);
}
}

// In a situation like the following:
// %0:subreg = instr ; DefMI, subreg = DstIdx
// %1 = copy %0:subreg ; CopyMI, SrcIdx = 0
Expand Down Expand Up @@ -1523,6 +1502,26 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
// sure that "undef" is not set.
if (NewIdx == 0)
NewMI.getOperand(0).setIsUndef(false);

// In a situation like the following:
//
// undef %2.subreg:reg = INST %1:reg ; DefMI (rematerializable),
// ; DefSubIdx = subreg
// %3:reg = COPY %2 ; SrcIdx = DstIdx = 0
// .... = SOMEINSTR %3:reg
//
// there are no subranges for %3 so after rematerialization we need
// to explicitly create them. Undefined subranges are removed later on.
if (DefSubIdx && !CP.getSrcIdx() && !CP.getDstIdx() &&
MRI->shouldTrackSubRegLiveness(DstReg) && !DstInt.hasSubRanges()) {
LaneBitmask FullMask = MRI->getMaxLaneMaskForVReg(DstReg);
LaneBitmask UsedLanes = TRI->getSubRegIndexLaneMask(DefSubIdx);
LaneBitmask UnusedLanes = FullMask & ~UsedLanes;
VNInfo::Allocator &Alloc = LIS->getVNInfoAllocator();
DstInt.createSubRangeFrom(Alloc, UsedLanes, DstInt);
DstInt.createSubRangeFrom(Alloc, UnusedLanes, DstInt);
}

// Add dead subregister definitions if we are defining the whole register
// but only part of it is live.
// This could happen if the rematerialization instruction is rematerializing
Expand Down
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