[llvm] [SCEV] Do not attempt to collect loop guards for loops without predecessor. (PR #123662)

[Florian Hahn via llvm-commits]

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@@ -336,3 +336,31 @@ exit:
   ret void
 
 }
+
+; Checks correct traversal for loops without a unique predecessor
+; outside the loop.
+define void @pr122913() {
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fhahn wrote:

Can the crash also be reproduced without one of the predecessors being unreachable?

Would be good to add a test case where `bb` is reachable if possible

https://github.com/llvm/llvm-project/pull/123662