[DFAJumpThreading] Update domtree lazily

Author: XChy

llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp

@@ -158,7 +158,7 @@ class DFAJumpThreading {
  void
  unfoldSelectInstrs(DominatorTree *DT,
  const SmallVector<SelectInstToUnfold, 4> &SelectInsts) {
- DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
+ DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
  SmallVector<SelectInstToUnfold, 4> Stack(SelectInsts);
 
  while (!Stack.empty()) {
@@ -975,8 +975,6 @@ 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()) {
@@ -993,15 +991,18 @@ struct TransformDFA {
  SmallPtrSet<BasicBlock *, 16> BlocksToClean;
  BlocksToClean.insert_range(successors(SwitchBlock));
 
- for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
- createExitPath(NewDefs, TPath, DuplicateMap, BlocksToClean, &DTU);
- NumPaths++;
- }
+ {
+ DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Lazy);
+ for (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 (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 (ThreadingPath &TPath : SwitchPaths->getThreadingPaths())
+ updateLastSuccessor(TPath, DuplicateMap, &DTU);
+ }
 
  // For each instruction that was cloned and used outside, update its uses
  updateSSA(NewDefs);