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LiveIntervalAnalysis: Mark subregister defs as undef when we determined they are only reading a dead superregister value

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This was not necessary before as this case can only be detected when the
liveness analysis is at subregister level.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226733 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun 2015-01-21 22:55:13 +00:00
parent f04568139a
commit 9a43e3d47f
3 changed files with 29 additions and 5 deletions
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5
include/llvm/CodeGen/MachineInstr.h
View File

@ -1048,6 +1048,11 @@ public:
bool addRegisterDead(unsigned Reg, const TargetRegisterInfo *RegInfo,
bool AddIfNotFound = false);
/// Mark all subregister defs of register @p Reg with the undef flag.
/// This function is used when we determined to have a subregister def in an
/// otherwise undefined super register.
void addRegisterDefReadUndef(unsigned Reg);
/// addRegisterDefined - We have determined MI defines a register. Make sure
/// there is an operand defining Reg.
void addRegisterDefined(unsigned Reg,

21
lib/CodeGen/LiveIntervalAnalysis.cpp
View File

@ -448,23 +448,34 @@ bool LiveIntervals::computeDeadValues(LiveInterval &LI,
for (auto VNI : LI.valnos) {
if (VNI->isUnused())
continue;
LiveRange::iterator I = LI.FindSegmentContaining(VNI->def);
SlotIndex Def = VNI->def;
LiveRange::iterator I = LI.FindSegmentContaining(Def);
assert(I != LI.end() && "Missing segment for VNI");
if (I->end != VNI->def.getDeadSlot())
// 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 " << VNI->def << " may separate interval\n");
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(VNI->def);
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: " << VNI->def << '\t' << *MI);
DEBUG(dbgs() << "All defs dead: " << Def << '\t' << *MI);
dead->push_back(MI);
}
}

8
lib/CodeGen/MachineInstr.cpp
View File

@ -1889,6 +1889,14 @@ bool MachineInstr::addRegisterDead(unsigned Reg,
return true;
}
void MachineInstr::addRegisterDefReadUndef(unsigned Reg) {
for (MachineOperand &MO : operands()) {
if (!MO.isReg() || !MO.isDef() || MO.getReg() != Reg || MO.getSubReg() == 0)
continue;
MO.setIsUndef();
}
}
void MachineInstr::addRegisterDefined(unsigned Reg,
const TargetRegisterInfo *RegInfo) {
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {