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VirtRegMap: No implicit defs/uses for super registers with subreg liveness tracking. 

Adding the implicit defs/uses to the superregisters is semantically questionable
but was not dangerous before as the register allocator never assigned the same
register to two overlapping LiveIntervals even when the actually live
subregisters do not overlap. With subregister liveness tracking enabled this
does actually happen and leads to subsequent bugs if we don't stop adding
the superregister defs/uses.

llvm-svn: 223892
This commit is contained in:
Matthias Braun 2014-12-10 01:13:04 +00:00
parent 587e27415d
commit d70caaf5a5
2 changed files with 33 additions and 5 deletions
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24
llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
View File

@ -671,6 +671,30 @@ void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
CancelKill = true;
break;
}
// If an instruction writes to a subregister, a new segment starts in the
// LiveInterval. In this case adding Kill-Flags is incorrect if no
// super registers defs/uses are appended to the instruction which is
// what we do when subregister liveness tracking is enabled.
if (MRI->tracksSubRegLiveness()) {
// Next segment has to be adjacent in the subregister write case.
LiveRange::iterator N = std::next(RI);
if (N != LI->end() && N->start == RI->end) {
// See if we have a partial write operand
bool IsFullWrite = false;
for (MachineInstr::const_mop_iterator MOp = MI->operands_begin(),
MOpE = MI->operands_end(); MOp != MOpE; ++MOp) {
if (MOp->isReg() && !MOp->isDef() && MOp->getReg() == Reg
&& MOp->getSubReg() == 0) {
IsFullWrite = true;
break;
}
}
if (!IsFullWrite)
CancelKill = true;
}
}
if (CancelKill)
MI->clearRegisterKills(Reg, nullptr);
else

14
llvm/lib/CodeGen/VirtRegMap.cpp
View File

@ -266,6 +266,7 @@ void VirtRegRewriter::addMBBLiveIns() {
}
void VirtRegRewriter::rewrite() {
bool NoSubRegLiveness = !MRI->tracksSubRegLiveness();
SmallVector<unsigned, 8> SuperDeads;
SmallVector<unsigned, 8> SuperDefs;
SmallVector<unsigned, 8> SuperKills;
@ -347,7 +348,8 @@ void VirtRegRewriter::rewrite() {
// A virtual register kill refers to the whole register, so we may
// have to add <imp-use,kill> operands for the super-register. A
// partial redef always kills and redefines the super-register.
if (MO.readsReg() && (MO.isDef() || MO.isKill()))
if (NoSubRegLiveness && MO.readsReg()
&& (MO.isDef() || MO.isKill()))
SuperKills.push_back(PhysReg);
if (MO.isDef()) {
@ -358,10 +360,12 @@ void VirtRegRewriter::rewrite() {
MO.setIsUndef(false);
// Also add implicit defs for the super-register.
if (MO.isDead())
SuperDeads.push_back(PhysReg);
else
SuperDefs.push_back(PhysReg);
if (NoSubRegLiveness) {
if (MO.isDead())
SuperDeads.push_back(PhysReg);
else
SuperDefs.push_back(PhysReg);
}
}
// PhysReg operands cannot have subregister indexes.