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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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37487 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -615,29 +615,41 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
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BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
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bool FalseBBDead = false;
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bool IterIfcvt = true;
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if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
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MergeBlocks(TrueBBI, FalseBBI);
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FalseBBDead = true;
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} else if (!isNextBlock(TrueBBI.BB, FalseBBI.BB)) {
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InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
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TrueBBI.hasFallThrough = false;
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if (BBI.ModifyPredicate || TrueBBI.ModifyPredicate)
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// Now ifcvt'd block will look like this:
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// BB:
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// ...
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// t, f = cmp
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// if t op
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// b BBf
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//
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// We cannot further ifcvt this block because the unconditional branch will
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// have to be predicated on the new condition, that will not be available
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// if cmp executes.
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bool isFallThrough = isNextBlock(TrueBBI.BB, FalseBBI.BB);
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if (!isFallThrough) {
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// Only merge them if the true block does not fallthrough to the false
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// block. By not merging them, we make it possible to iteratively
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// ifcvt the blocks.
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if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
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MergeBlocks(TrueBBI, FalseBBI);
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FalseBBDead = true;
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// Mixed predicated and unpredicated code. This cannot be iteratively
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// predicated.
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IterIfcvt = false;
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} else {
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InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
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TrueBBI.hasFallThrough = false;
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if (BBI.ModifyPredicate || TrueBBI.ModifyPredicate)
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// Now ifcvt'd block will look like this:
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// BB:
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// ...
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// t, f = cmp
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// if t op
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// b BBf
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//
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// We cannot further ifcvt this block because the unconditional branch will
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// have to be predicated on the new condition, that will not be available
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// if cmp executes.
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IterIfcvt = false;
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}
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}
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// Now merge the entry of the triangle with the true block.
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BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
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MergeBlocks(BBI, TrueBBI);
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// Remove entry to false edge.
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if (BBI.BB->isSuccessor(FalseBBI.BB))
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BBI.BB->removeSuccessor(FalseBBI.BB);
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std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
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std::back_inserter(BBI.Predicate));
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