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Tail duplication should zap a copy it inserted for SSA update if the copy is the only use of its source.

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llvm-svn: 91390
This commit is contained in:
Evan Cheng 2009-12-15 01:44:10 +00:00
parent cd8f0de016
commit d6a991f735
1 changed files with 37 additions and 13 deletions
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50
lib/CodeGen/TailDuplication.cpp
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@ -90,7 +90,8 @@ namespace {
SmallSetVector<MachineBasicBlock*, 8> &Succs);
bool TailDuplicateBlocks(MachineFunction &MF);
bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
SmallVector<MachineBasicBlock*, 8> &TDBBs);
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallVector<MachineInstr*, 16> &Copies);
void RemoveDeadBlock(MachineBasicBlock *MBB);
};
@ -194,7 +195,8 @@ bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
MBB->succ_end());
SmallVector<MachineBasicBlock*, 8> TDBBs;
if (TailDuplicate(MBB, MF, TDBBs)) {
SmallVector<MachineInstr*, 16> Copies;
if (TailDuplicate(MBB, MF, TDBBs, Copies)) {
++NumTails;
// TailBB's immediate successors are now successors of those predecessors
@ -251,6 +253,21 @@ bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
SSAUpdateVals.clear();
}
// Eliminate some of the copies inserted tail duplication to maintain
// SSA form.
for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
MachineInstr *Copy = Copies[i];
unsigned Src, Dst, SrcSR, DstSR;
if (TII->isMoveInstr(*Copy, Src, Dst, SrcSR, DstSR)) {
MachineRegisterInfo::use_iterator UI = MRI->use_begin(Src);
if (++UI == MRI->use_end()) {
// Copy is the only use. Do trivial copy propagation here.
MRI->replaceRegWith(Dst, Src);
Copy->eraseFromParent();
}
}
}
if (PreRegAlloc && TailDupVerify)
VerifyPHIs(MF, false);
MadeChange = true;
@ -418,7 +435,8 @@ TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
/// of its predecessors.
bool
TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
SmallVector<MachineBasicBlock*, 8> &TDBBs) {
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallVector<MachineInstr*, 16> &Copies) {
// Don't try to tail-duplicate single-block loops.
if (TailBB->isSuccessor(TailBB))
return false;
@ -502,7 +520,7 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
// Clone the contents of TailBB into PredBB.
DenseMap<unsigned, unsigned> LocalVRMap;
SmallVector<std::pair<unsigned,unsigned>, 4> Copies;
SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
MachineBasicBlock::iterator I = TailBB->begin();
while (I != TailBB->end()) {
MachineInstr *MI = &*I;
@ -510,7 +528,7 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
if (MI->getOpcode() == TargetInstrInfo::PHI) {
// Replace the uses of the def of the PHI with the register coming
// from PredBB.
ProcessPHI(MI, TailBB, PredBB, LocalVRMap, Copies);
ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos);
} else {
// Replace def of virtual registers with new registers, and update
// uses with PHI source register or the new registers.
@ -518,9 +536,12 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
}
}
MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator();
for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
const TargetRegisterClass *RC = MRI->getRegClass(Copies[i].first);
TII->copyRegToReg(*PredBB, Loc, Copies[i].first, Copies[i].second, RC, RC);
for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
const TargetRegisterClass *RC = MRI->getRegClass(CopyInfos[i].first);
TII->copyRegToReg(*PredBB, Loc, CopyInfos[i].first,
CopyInfos[i].second, RC,RC);
MachineInstr *CopyMI = prior(Loc);
Copies.push_back(CopyMI);
}
NumInstrDups += TailBB->size() - 1; // subtract one for removed branch
@ -553,14 +574,14 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
<< "From MBB: " << *TailBB);
if (PreRegAlloc) {
DenseMap<unsigned, unsigned> LocalVRMap;
SmallVector<std::pair<unsigned,unsigned>, 4> Copies;
SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
MachineBasicBlock::iterator I = TailBB->begin();
// Process PHI instructions first.
while (I != TailBB->end() && I->getOpcode() == TargetInstrInfo::PHI) {
// Replace the uses of the def of the PHI with the register coming
// from PredBB.
MachineInstr *MI = &*I++;
ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, Copies);
ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos);
if (MI->getParent())
MI->eraseFromParent();
}
@ -574,9 +595,12 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
MI->eraseFromParent();
}
MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator();
for (unsigned i = 0, e = Copies.size(); i != e; ++i) {
const TargetRegisterClass *RC = MRI->getRegClass(Copies[i].first);
TII->copyRegToReg(*PrevBB, Loc, Copies[i].first, Copies[i].second, RC, RC);
for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) {
const TargetRegisterClass *RC = MRI->getRegClass(CopyInfos[i].first);
TII->copyRegToReg(*PrevBB, Loc, CopyInfos[i].first,
CopyInfos[i].second, RC, RC);
MachineInstr *CopyMI = prior(Loc);
Copies.push_back(CopyMI);
}
} else {
// No PHIs to worry about, just splice the instructions over.