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

[Philip Reames via llvm-commits]

================
@@ -364,3 +364,29 @@ body:
 exit:
   ret void
 }
+
+define void @hang_due_to_unreachable_phi_inblock() personality ptr null {
+bb:
+  br label %bb6
+
+self-loop:                                        ; preds = %self-loop
+  %dead = invoke ptr null()
+          to label %self-loop unwind label %bb4
----------------
preames wrote:

I tried that, and it no longer hung on old opt.  I might have gone too simple (I used a poison condition), but I suspect we might special case that idiom somewhere.  I'll give it one more go before landing to be sure.  

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