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ifcvt a triangle: don't merge ifcvt block with rejoin block if it can fall through to it. If merged, the resulting block is not a candidate for iterative ifcvting since it contains both predicated and non-predicated code. 

llvm-svn: 37487
This commit is contained in:
Evan Cheng 2007-06-07 08:13:00 +00:00
parent 0ae22e99c8
commit d3f3f0adad
1 changed files with 29 additions and 17 deletions
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46
llvm/lib/CodeGen/IfConversion.cpp
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@ -615,29 +615,41 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
bool FalseBBDead = false;
bool IterIfcvt = true;
if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
MergeBlocks(TrueBBI, FalseBBI);
FalseBBDead = true;
} else if (!isNextBlock(TrueBBI.BB, FalseBBI.BB)) {
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
TrueBBI.hasFallThrough = false;
if (BBI.ModifyPredicate || TrueBBI.ModifyPredicate)
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch will
// have to be predicated on the new condition, that will not be available
// if cmp executes.
bool isFallThrough = isNextBlock(TrueBBI.BB, FalseBBI.BB);
if (!isFallThrough) {
// Only merge them if the true block does not fallthrough to the false
// block. By not merging them, we make it possible to iteratively
// ifcvt the blocks.
if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
MergeBlocks(TrueBBI, FalseBBI);
FalseBBDead = true;
// Mixed predicated and unpredicated code. This cannot be iteratively
// predicated.
IterIfcvt = false;
} else {
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
TrueBBI.hasFallThrough = false;
if (BBI.ModifyPredicate || TrueBBI.ModifyPredicate)
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch will
// have to be predicated on the new condition, that will not be available
// if cmp executes.
IterIfcvt = false;
}
}
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, TrueBBI);
// Remove entry to false edge.
if (BBI.BB->isSuccessor(FalseBBI.BB))
BBI.BB->removeSuccessor(FalseBBI.BB);
std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
std::back_inserter(BBI.Predicate));