[llvm] [SCEV] Fix a hang introduced by collectForPHI (PR #158153)

[Philip Reames via llvm-commits]

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@@ -364,3 +364,34 @@ body:
 exit:
   ret void
 }
+
+define void @hang_due_to_unreachable_phi_inblock() personality ptr null {
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preames wrote:

Yep, that was the problem.  Fixed, and cleaned up the test a bit manually as well.  

https://github.com/llvm/llvm-project/pull/158153