[llvm] [SCEV][LV] Invalidate LCSSA exit phis more thoroughly (PR #69909)

[Florian Hahn via llvm-commits]

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@@ -8408,6 +8408,35 @@ void ScalarEvolution::forgetValue(Value *V) {
   forgetMemoizedResults(ToForget);
 }
 
+void ScalarEvolution::forgetLcssaPhiWithNewPredecessor(PHINode *V) {
+  // If SCEV looked through a trivial LCSSA phi node, we might have SCEV's
+  // directly using a SCEVUnknown defined in the loop. After an extra
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fhahn wrote:

Is this accurate? `follow` has a comment that it *could* be restricted, but isn't at the moment AFAICT?

https://github.com/llvm/llvm-project/pull/69909