From d4c22859db8a3ac3ea11d9fdede28dcb57f3aee1 Mon Sep 17 00:00:00 2001
From: Alexis Engelke <engelke@in.tum.de>
Date: Mon, 16 Mar 2026 16:07:49 +0100
Subject: [PATCH] [DomTree] Assert non-null block for pre-dom tree (#186790)

In a pre-dominator tree, blocks should never be null.
---
 llvm/include/llvm/Support/GenericDomTree.h      | 8 ++++++--
 llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp | 2 ++
 polly/lib/Analysis/ScopBuilder.cpp              | 2 +-
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/Support/GenericDomTree.h b/llvm/include/llvm/Support/GenericDomTree.h
index 832b6e02daf5..920983e7bd80 100644
--- a/llvm/include/llvm/Support/GenericDomTree.h
+++ b/llvm/include/llvm/Support/GenericDomTree.h
@@ -384,11 +384,15 @@ protected:
 private:
   std::optional<unsigned> getNodeIndex(const NodeT *BB) const {
     if constexpr (GraphHasNodeNumbers<NodeT *>) {
-      // BB can be nullptr, map nullptr to index 0.
       assert(BlockNumberEpoch ==
                  GraphTraits<ParentPtr>::getNumberEpoch(Parent) &&
              "dominator tree used with outdated block numbers");
-      return BB ? GraphTraits<const NodeT *>::getNumber(BB) + 1 : 0;
+      if constexpr (IsPostDom) {
+        if (!BB)
+          return 0; // BB may be nullptr for post-dominator tree, map to 0.
+      } else
+        assert(BB && "dominator tree block must be non-null");
+      return GraphTraits<const NodeT *>::getNumber(BB) + 1;
     } else {
       if (auto It = NodeNumberMap.find(BB); It != NodeNumberMap.end())
         return It->second;
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 97ba8eee6742..6b459e046da3 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -28333,6 +28333,8 @@ bool SLPVectorizerPass::vectorizeGEPIndices(BasicBlock *BB, BoUpSLP &R) {
         const SCEV *SCEVI = SE->getSCEV(GEPList[I]);
         for (int J = I + 1; J < E && Candidates.size() > 1; ++J) {
           auto *GEPJ = GEPList[J];
+          if (!Candidates.count(GEPJ))
+            continue;
           const SCEV *SCEVJ = SE->getSCEV(GEPList[J]);
           if (isa<SCEVConstant>(SE->getMinusSCEV(SCEVI, SCEVJ))) {
             Candidates.remove(GEPI);
diff --git a/polly/lib/Analysis/ScopBuilder.cpp b/polly/lib/Analysis/ScopBuilder.cpp
index 1ea9a554f761..f4d654fa74cb 100644
--- a/polly/lib/Analysis/ScopBuilder.cpp
+++ b/polly/lib/Analysis/ScopBuilder.cpp
@@ -637,7 +637,7 @@ void ScopBuilder::propagateDomainConstraintsToRegionExit(
   auto *RI = scop->getRegion().getRegionInfo();
   auto *BBReg = RI ? RI->getRegionFor(BB) : nullptr;
   auto *ExitBB = BBReg ? BBReg->getExit() : nullptr;
-  if (!BBReg || BBReg->getEntry() != BB || !scop->contains(ExitBB))
+  if (!BBReg || BBReg->getEntry() != BB || !ExitBB || !scop->contains(ExitBB))
     return;
 
   // Do not propagate the domain if there is a loop backedge inside the region