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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179199 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCInstrInfo.cpp b/lib/Target/PowerPC/PPCInstrInfo.cpp
index 8abe5ff..c967457 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -876,6 +876,29 @@
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) {
diff --git a/lib/Target/PowerPC/PPCInstrInfo.h b/lib/Target/PowerPC/PPCInstrInfo.h
index a6ab617..b5fcc85 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.h
+++ b/lib/Target/PowerPC/PPCInstrInfo.h
@@ -173,9 +173,7 @@
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,