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[SimplifyCFG][NFC] Improve compile time for TryToSimplifyUncondBranchFromEmptyBlock optimization. #110715

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Merged
merged 3 commits into from
Oct 9, 2024
Merged

[SimplifyCFG][NFC] Improve compile time for TryToSimplifyUncondBranchFromEmptyBlock optimization. #110715

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03d9ec6
[SimplifyCFG][NFC] Improve compile time for TryToSimplifyUncondBranch…
aemerson Oct 2, 2024
7a4c521
Don't unnecessarily cache.
aemerson Oct 7, 2024
1e602db
Sink SuccPreds further.
aemerson Oct 8, 2024
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11 changes: 5 additions & 6 deletions llvm/lib/Transforms/Utils/Local.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1023,7 +1023,6 @@ static void replaceUndefValuesInPhi(PHINode *PN,
static bool
CanRedirectPredsOfEmptyBBToSucc(BasicBlock *BB, BasicBlock *Succ,
const SmallPtrSetImpl<BasicBlock *> &BBPreds,
const SmallPtrSetImpl<BasicBlock *> &SuccPreds,
BasicBlock *&CommonPred) {

// There must be phis in BB, otherwise BB will be merged into Succ directly
Expand All @@ -1042,7 +1041,7 @@ CanRedirectPredsOfEmptyBBToSucc(BasicBlock *BB, BasicBlock *Succ,

// Get the single common predecessor of both BB and Succ. Return false
// when there are more than one common predecessors.
for (BasicBlock *SuccPred : SuccPreds) {
for (BasicBlock *SuccPred : predecessors(Succ)) {
if (BBPreds.count(SuccPred)) {
if (CommonPred)
return false;
Expand Down Expand Up @@ -1166,7 +1165,6 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
return false;

SmallPtrSet<BasicBlock *, 16> BBPreds(pred_begin(BB), pred_end(BB));
SmallPtrSet<BasicBlock *, 16> SuccPreds(pred_begin(Succ), pred_end(Succ));

// The single common predecessor of BB and Succ when BB cannot be killed
BasicBlock *CommonPred = nullptr;
Expand All @@ -1175,13 +1173,14 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,

// Even if we can not fold BB into Succ, we may be able to redirect the
// predecessors of BB to Succ.
bool BBPhisMergeable =
BBKillable ||
CanRedirectPredsOfEmptyBBToSucc(BB, Succ, BBPreds, SuccPreds, CommonPred);
bool BBPhisMergeable = BBKillable || CanRedirectPredsOfEmptyBBToSucc(
BB, Succ, BBPreds, CommonPred);

if ((!BBKillable && !BBPhisMergeable) || introduceTooManyPhiEntries(BB, Succ))
return false;

SmallPtrSet<BasicBlock *, 16> SuccPreds(pred_begin(Succ), pred_end(Succ));
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@nikic nikic Oct 8, 2024

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I'd move this further down to where it's actually needed now.


// Check to see if merging these blocks/phis would cause conflicts for any of
// the phi nodes in BB or Succ. If not, we can safely merge.

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