[llvm] [LoopFusion] Remove DT edge from Extiblock to ExitBlockSuc (PR #193641)

[Afonso Rafael via llvm-commits]

https://github.com/Alf0nso updated https://github.com/llvm/llvm-project/pull/193641

>From 7a6374629d550de6d067fd7f2bc67dcab55943bf Mon Sep 17 00:00:00 2001
From: Afonso Rafael <afonsorafael at sapo.pt>
Date: Thu, 23 Apr 2026 00:11:50 +0000
Subject: [PATCH] [LoopFusion] Remove DT edge from Extiblock to ExitBlockSuc

This patch fixes the following assertion failure:
https://www.godbolt.org/z/ejEhYchPq

To remove the node, it cannot have successors, if this edge is not
removed, when applying the updates to the DT the following assertion
will appear:
"Assertion `Node->isLeaf() && "Node is not a leaf node."' failed"

This assertion does not always fail because before applying the
updates on the "GenericDomTreeContruction", "ApplyUpdates" function it
runs CalculateFromScratch on some situations:

    // Make unittests of the incremental algorithm work
    if (DT.DomTreeNodes.size() <= 100) {
      if (BUI.NumLegalized > DT.DomTreeNodes.size())
        CalculateFromScratch(DT, &BUI);
    } else if (BUI.NumLegalized > DT.DomTreeNodes.size() / 40)
      CalculateFromScratch(DT, &BUI);
---
 llvm/lib/Transforms/Scalar/LoopFuse.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/llvm/lib/Transforms/Scalar/LoopFuse.cpp b/llvm/lib/Transforms/Scalar/LoopFuse.cpp
index be543062670c6..6de3fc0174d7d 100644
--- a/llvm/lib/Transforms/Scalar/LoopFuse.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopFuse.cpp
@@ -1818,6 +1818,8 @@ struct LoopFuser {
         DominatorTree::Insert, FC0GuardBlock, FC1NonLoopBlock));
 
     if (FC0.Peeled) {
+      TreeUpdates.emplace_back(DominatorTree::UpdateType(
+          DominatorTree::Delete, FC0.ExitBlock, FC0ExitBlockSuccessor));
       // Remove the Block after the ExitBlock of FC0
       TreeUpdates.emplace_back(DominatorTree::UpdateType(
           DominatorTree::Delete, FC0ExitBlockSuccessor, FC1GuardBlock));