[llvm] ed113e7 - [DFAJumpThreading] Update domtree lazily (#162240)

[via llvm-commits]

Author: Hongyu Chen
Date: 2025-10-07T10:37:37Z
New Revision: ed113e7904943565b4cd05588f6b639e40187510

URL: https://github.com/llvm/llvm-project/commit/ed113e7904943565b4cd05588f6b639e40187510
DIFF: https://github.com/llvm/llvm-project/commit/ed113e7904943565b4cd05588f6b639e40187510.diff

LOG: [DFAJumpThreading] Update domtree lazily (#162240)

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp b/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
index 3b75475a5277e..9f0bd37451820 100644
--- a/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
@@ -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()) {
@@ -977,8 +978,6 @@ 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()) {
@@ -995,15 +994,18 @@ 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);