[llvm] [LV] Don't vectorize if trip count expansion may introduce UB. (PR #92177)

[Florian Hahn via llvm-commits]

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@@ -161,6 +161,11 @@ SCEVExpander::findInsertPointAfter(Instruction *I,
   return IP;
 }
 
+bool SCEVExpander::expansionMayIntroduceUB(const SCEV *Expr) {
+  return SCEVExprContains(Expr,
+                          [](const SCEV *Op) { return isa<SCEVUDivExpr>(Op); });
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fhahn wrote:

Sorry for just coming back to this now!

> In the given example, c has to be zero, I think? If c isn't zero, and b is zero, we divide by zero even before any optimizations run.

Ah yes, updated to rewrite the expression, thanks!

> Can we not use isSafeToExpand() for some reason?

Updated as well in the latest version, thanks!



https://github.com/llvm/llvm-project/pull/92177