[llvm-branch-commits] [llvm] 409361c - Revert "[LoopBoundSplit] Fix edge connections during transformation (#192106)"

[via llvm-branch-commits]

Author: Congzhe Cao
Date: 2026-05-29T09:57:16-04:00
New Revision: 409361c57949c6a3586a1f8b6015eccf628acfb8

URL: https://github.com/llvm/llvm-project/commit/409361c57949c6a3586a1f8b6015eccf628acfb8
DIFF: https://github.com/llvm/llvm-project/commit/409361c57949c6a3586a1f8b6015eccf628acfb8.diff

LOG: Revert "[LoopBoundSplit] Fix edge connections during transformation (#192106)"

This reverts commit fa44ca8e5ef6f57c03ba55a4c7b944c9a3ee633e.

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp b/llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp
index 27ccce3328d27..a461e1f7fe074 100644
--- a/llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp
@@ -356,19 +356,6 @@ static bool splitLoopBound(Loop &L, DominatorTree &DT, LoopInfo &LI,
   BasicBlock *PostLoopPreHeader = PostLoop->getLoopPreheader();
   IRBuilder<> Builder(&PostLoopPreHeader->front());
 
-  // Replace exit branch target of pre-loop by post-loop's preheader.
-  // Note: update the branch here after calling cloneLoopWithPreheader()
-  // to keep the IR valid.
-  if (L.getExitBlock() == ExitingCond.BI->getSuccessor(0))
-    ExitingCond.BI->setSuccessor(0, PostLoopPreHeader);
-  else
-    ExitingCond.BI->setSuccessor(1, PostLoopPreHeader);
-
-  // Update dominator tree.
-  DT.changeImmediateDominator(PostLoopPreHeader, L.getExitingBlock());
-#ifndef NDEBUG
-  LI.verify(DT);
-#endif
   // Update phi nodes in header of post-loop.
   bool isExitingLatch = L.getExitingBlock() == L.getLoopLatch();
   Value *ExitingCondLCSSAPhi = nullptr;
@@ -390,8 +377,6 @@ static bool splitLoopBound(Loop &L, DominatorTree &DT, LoopInfo &LI,
     // Find PHI with exiting condition from pre-loop. The PHI should be
     // SCEVAddRecExpr and have same incoming value from backedge with
     // ExitingCond.
-    //
-    // TODO: Separate SCEV queries from PHI node updates.
     if (!SE.isSCEVable(PN.getType()))
       continue;
 
@@ -401,22 +386,13 @@ static bool splitLoopBound(Loop &L, DominatorTree &DT, LoopInfo &LI,
       ExitingCondLCSSAPhi = LCSSAPhi;
   }
 
-  // Add conditional branch to check we can skip post-loop in its preheader,
-  // and update DT.
+  // Add conditional branch to check we can skip post-loop in its preheader.
   Instruction *OrigBI = PostLoopPreHeader->getTerminator();
   ICmpInst::Predicate Pred = ICmpInst::ICMP_NE;
   Value *Cond =
       Builder.CreateICmp(Pred, ExitingCondLCSSAPhi, ExitingCond.BoundValue);
   Builder.CreateCondBr(Cond, PostLoop->getHeader(), PostLoop->getExitBlock());
   OrigBI->eraseFromParent();
-  DT.changeImmediateDominator(PostLoop->getExitBlock(), PostLoopPreHeader);
-#ifdef EXPENSIVE_CHECKS
-  assert(DT.verify(DominatorTree::VerificationLevel::Full) &&
-         "DT broken during transformation!");
-#else
-  assert(DT.verify(DominatorTree::VerificationLevel::Fast) &&
-         "DT broken during transformation!");
-#endif
 
   // Create new loop bound and add it into preheader of pre-loop.
   const SCEV *NewBoundSCEV = ExitingCond.BoundSCEV;
@@ -443,6 +419,12 @@ static bool splitLoopBound(Loop &L, DominatorTree &DT, LoopInfo &LI,
       cast<CondBrInst>(VMap[SplitCandidateCond.BI]);
   ClonedSplitCandidateBI->setCondition(ConstantInt::getFalse(Context));
 
+  // Replace exit branch target of pre-loop by post-loop's preheader.
+  if (L.getExitBlock() == ExitingCond.BI->getSuccessor(0))
+    ExitingCond.BI->setSuccessor(0, PostLoopPreHeader);
+  else
+    ExitingCond.BI->setSuccessor(1, PostLoopPreHeader);
+
   // Update phi node in exit block of post-loop.
   Builder.SetInsertPoint(PostLoopPreHeader, PostLoopPreHeader->begin());
   for (PHINode &PN : PostLoop->getExitBlock()->phis()) {
@@ -467,6 +449,10 @@ static bool splitLoopBound(Loop &L, DominatorTree &DT, LoopInfo &LI,
     }
   }
 
+  // Update dominator tree.
+  DT.changeImmediateDominator(PostLoopPreHeader, L.getExitingBlock());
+  DT.changeImmediateDominator(PostLoop->getExitBlock(), PostLoopPreHeader);
+
   // Invalidate cached SE information.
   SE.forgetLoop(&L);