[llvm] [LV] Add assertion for loop predecessor (and terminator of) existing when checking out of loop inst for poison (PR #154603)

[via llvm-commits]

https://github.com/calebwat created https://github.com/llvm/llvm-project/pull/154603

In LoopVectorizationLegality, TheLoop->getLoopPredecessor() and [...]Predecessor()->getTerminator() are used without a null check. This patch adds an assert that they are non-null, since they are expected to be defined.

>From 7b292d25c4c80a694a9798b8b213352335849cef Mon Sep 17 00:00:00 2001
From: "Watts, Caleb" <caleb.watts at intel.com>
Date: Wed, 20 Aug 2025 13:04:51 -0700
Subject: [PATCH] [LV] Add assertion for loop predecessor (and terminator of)
 existing when checking out of loop inst for poison

In LoopVectorizationLegality, TheLoop->getLoopPredecessor() and [...]Predecessor()->getTerminator() are used without a null check. This patch adds an assert that they are non-null, since they are expected to be defined.
---
 llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 789047a2a28e7..5882b2b5466d9 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -1527,6 +1527,11 @@ bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
           if (!CurrI || !TheLoop->contains(CurrI)) {
             // If operands from outside the loop may be poison then Ptr may also
             // be poison.
+            assert((TheLoop->getLoopPredecessor() &&
+                    TheLoop->getLoopPredecessor()->getTerminator()) &&
+                   "No loop predecessor/pred terminator found while checking "
+                   "out of loop instruction for poison");
+
             if (!isGuaranteedNotToBePoison(CurrV, AC,
                                            TheLoop->getLoopPredecessor()
                                                ->getTerminator()