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RegisterCoalescer: rewrite eliminateUndefCopy(). 

This also fixes problems with undef copies of subregisters. I can't
attach a testcase for that as none of the targets in trunk has
subregister liveness tracking enabled.

llvm-svn: 224560
This commit is contained in:
Matthias Braun 2014-12-19 01:39:46 +00:00
parent 3a95b5bce2
commit aeb50b3805
1 changed files with 64 additions and 29 deletions
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93
llvm/lib/CodeGen/RegisterCoalescer.cpp
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@ -204,7 +204,7 @@ namespace {
void updateRegDefsUses(unsigned SrcReg, unsigned DstReg, unsigned SubIdx);
/// Handle copies of undef values.
bool eliminateUndefCopy(MachineInstr *CopyMI, const CoalescerPair &CP);
bool eliminateUndefCopy(MachineInstr *CopyMI);
public:
static char ID; // Class identification, replacement for typeinfo
@ -1026,6 +1026,13 @@ bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
return true;
}
static void removeUndefValue(LiveRange &LR, SlotIndex At)
{
VNInfo *VNInfo = LR.getVNInfoAt(At);
assert(VNInfo != nullptr && SlotIndex::isSameInstr(VNInfo->def, At));
LR.removeValNo(VNInfo);
}
/// ProcessImpicitDefs may leave some copies of <undef>
/// values, it only removes local variables. When we have a copy like:
///
@ -1033,43 +1040,72 @@ bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
///
/// We delete the copy and remove the corresponding value number from %vreg1.
/// Any uses of that value number are marked as <undef>.
bool RegisterCoalescer::eliminateUndefCopy(MachineInstr *CopyMI,
const CoalescerPair &CP) {
bool RegisterCoalescer::eliminateUndefCopy(MachineInstr *CopyMI) {
// Note that we do not query CoalescerPair here but redo isMoveInstr as the
// CoalescerPair may have a new register class with adjusted subreg indices
// at this point.
unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
isMoveInstr(*TRI, CopyMI, SrcReg, DstReg, SrcSubIdx, DstSubIdx);
SlotIndex Idx = LIS->getInstructionIndex(CopyMI);
LiveInterval *SrcInt = &LIS->getInterval(CP.getSrcReg());
if (SrcInt->liveAt(Idx))
return false;
LiveInterval *DstInt = &LIS->getInterval(CP.getDstReg());
if (DstInt->liveAt(Idx))
const LiveInterval &SrcLI = LIS->getInterval(SrcReg);
// CopyMI is undef iff SrcReg is not live before the instruction.
if (SrcSubIdx != 0 && SrcLI.hasSubRanges()) {
unsigned SrcMask = TRI->getSubRegIndexLaneMask(SrcSubIdx);
for (const LiveInterval::SubRange &SR : SrcLI.subranges()) {
if ((SR.LaneMask & SrcMask) == 0)
continue;
if (SR.liveAt(Idx))
return false;
}
} else if (SrcLI.liveAt(Idx))
return false;
// No intervals are live-in to CopyMI - it is undef.
if (CP.isFlipped())
DstInt = SrcInt;
SrcInt = nullptr;
DEBUG(dbgs() << "\tEliminating copy of <undef> value\n");
// Remove any DstReg segments starting at the instruction.
LiveInterval &DstLI = LIS->getInterval(DstReg);
unsigned DstMask = TRI->getSubRegIndexLaneMask(DstSubIdx);
SlotIndex RegIndex = Idx.getRegSlot();
VNInfo *DeadVNI = DstInt->getVNInfoAt(RegIndex);
assert(DeadVNI && "No value defined in DstInt");
DstInt->removeValNo(DeadVNI);
// Eliminate the corresponding values in the subregister ranges.
for (LiveInterval::SubRange &S : DstInt->subranges()) {
VNInfo *DeadVNI = S.getVNInfoAt(RegIndex);
if (DeadVNI == nullptr)
for (LiveInterval::SubRange &SR : DstLI.subranges()) {
if ((SR.LaneMask & DstMask) == 0)
continue;
S.removeValNo(DeadVNI);
removeUndefValue(SR, RegIndex);
DstLI.removeEmptySubRanges();
}
// Remove value or merge with previous one in case of a subregister def.
if (VNInfo *PrevVNI = DstLI.getVNInfoAt(Idx)) {
VNInfo *VNInfo = DstLI.getVNInfoAt(RegIndex);
DstLI.MergeValueNumberInto(VNInfo, PrevVNI);
} else {
removeUndefValue(DstLI, RegIndex);
}
// Find new undef uses.
for (MachineOperand &MO : MRI->reg_nodbg_operands(DstInt->reg)) {
if (MO.isDef() || MO.isUndef())
// Mark uses as undef.
for (MachineOperand &MO : MRI->reg_nodbg_operands(DstReg)) {
if (MO.isDef() /*|| MO.isUndef()*/)
continue;
MachineInstr *MI = MO.getParent();
SlotIndex Idx = LIS->getInstructionIndex(MI);
if (DstInt->liveAt(Idx))
const MachineInstr &MI = *MO.getParent();
SlotIndex UseIdx = LIS->getInstructionIndex(&MI);
unsigned UseMask = TRI->getSubRegIndexLaneMask(MO.getSubReg());
bool isLive;
if (UseMask != ~0u && DstLI.hasSubRanges()) {
isLive = false;
for (const LiveInterval::SubRange &SR : DstLI.subranges()) {
if ((SR.LaneMask & UseMask) == 0)
continue;
if (SR.liveAt(UseIdx)) {
isLive = true;
break;
}
}
} else
isLive = DstLI.liveAt(UseIdx);
if (isLive)
continue;
MO.setIsUndef(true);
DEBUG(dbgs() << "\tnew undef: " << Idx << '\t' << *MI);
DEBUG(dbgs() << "\tnew undef: " << UseIdx << '\t' << MI);
}
return true;
}
@ -1227,8 +1263,7 @@ bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
}
// Eliminate undefs.
if (!CP.isPhys() && eliminateUndefCopy(CopyMI, CP)) {
DEBUG(dbgs() << "\tEliminated copy of <undef> value.\n");
if (!CP.isPhys() && eliminateUndefCopy(CopyMI)) {
LIS->RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
return false; // Not coalescable.