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PPC: Don't predicate a diamond with two counter decrements 

I've not seen this happen in practice, and probably can't until we start
allowing decrement-counter-based conditional branches to be double predicated,
but just in case, don't allow predication of a diamond in which both sides have
ctr-defining branches. Even though the branching behavior of these can be
predicated, the counter-decrementing behavior cannot be.

llvm-svn: 179199
This commit is contained in:
Hal Finkel 2013-04-10 18:30:16 +00:00
parent ea1d1a2d05
commit 30ae229141
2 changed files with 24 additions and 3 deletions
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23
llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
View File

@ -876,6 +876,29 @@ bool PPCInstrInfo::FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,
return true;
}
static bool MBBDefinesCTR(MachineBasicBlock &MBB) {
for (MachineBasicBlock::iterator I = MBB.begin(), IE = MBB.end();
I != IE; ++I)
if (I->definesRegister(PPC::CTR) || I->definesRegister(PPC::CTR8))
return true;
return false;
}
// We should make sure that, if we're going to predicate both sides of a
// condition (a diamond), that both sides don't define the counter register. We
// can predicate counter-decrement-based branches, but while that predicates
// the branching, it does not predicate the counter decrement. If we tried to
// merge the triangle into one predicated block, we'd decrement the counter
// twice.
bool PPCInstrInfo::isProfitableToIfCvt(MachineBasicBlock &TMBB,
unsigned NumT, unsigned ExtraT,
MachineBasicBlock &FMBB,
unsigned NumF, unsigned ExtraF,
const BranchProbability &Probability) const {
return !(MBBDefinesCTR(TMBB) && MBBDefinesCTR(FMBB));
}
bool PPCInstrInfo::isPredicated(const MachineInstr *MI) const {
unsigned OpC = MI->getOpcode();
switch (OpC) {

4
llvm/lib/Target/PowerPC/PPCInstrInfo.h
View File

@ -173,9 +173,7 @@ public:
unsigned NumT, unsigned ExtraT,
MachineBasicBlock &FMBB,
unsigned NumF, unsigned ExtraF,
const BranchProbability &Probability) const {
return true;
}
const BranchProbability &Probability) const;
virtual bool isProfitableToDupForIfCvt(MachineBasicBlock &MBB,
unsigned NumCycles,