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[DFAJumpThreading] Update domtree lazily #162240

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Merged
merged 2 commits into from
Oct 7, 2025
Merged

[DFAJumpThreading] Update domtree lazily #162240

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abbaaac
[DFAJumpThreading] Update domtree lazily
XChy Oct 7, 2025
b21f1e3
add todo
XChy Oct 7, 2025
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24 changes: 13 additions & 11 deletions llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,8 @@ class DFAJumpThreading {
void
unfoldSelectInstrs(DominatorTree *DT,
const SmallVector<SelectInstToUnfold, 4> &SelectInsts) {
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
// TODO: Have everything use a single lazy DTU
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
SmallVector<SelectInstToUnfold, 4> Stack(SelectInsts);

while (!Stack.empty()) {
Expand Down Expand Up @@ -975,8 +976,6 @@ struct TransformDFA {

/// Transform each threading path to effectively jump thread the DFA.
void createAllExitPaths() {
DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Eager);

// Move the switch block to the end of the path, since it will be duplicated
BasicBlock *SwitchBlock = SwitchPaths->getSwitchBlock();
for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
Expand All @@ -993,15 +992,18 @@ struct TransformDFA {
SmallPtrSet<BasicBlock *, 16> BlocksToClean;
BlocksToClean.insert_range(successors(SwitchBlock));

for (const ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
createExitPath(NewDefs, TPath, DuplicateMap, BlocksToClean, &DTU);
NumPaths++;
}
{
DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Lazy);
for (const ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
createExitPath(NewDefs, TPath, DuplicateMap, BlocksToClean, &DTU);
NumPaths++;
}

// After all paths are cloned, now update the last successor of the cloned
// path so it skips over the switch statement
for (const ThreadingPath &TPath : SwitchPaths->getThreadingPaths())
updateLastSuccessor(TPath, DuplicateMap, &DTU);
// After all paths are cloned, now update the last successor of the cloned
// path so it skips over the switch statement
for (const ThreadingPath &TPath : SwitchPaths->getThreadingPaths())
updateLastSuccessor(TPath, DuplicateMap, &DTU);
}

// For each instruction that was cloned and used outside, update its uses
updateSSA(NewDefs);
Expand Down
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