[llvm] [InstCombine] Check for undef before transforming lshr (mul (X, 2^N + 1)), N -> add (X, lshr(X, N)) (PR #96324)

[Nikita Popov via llvm-commits]

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@@ -1499,7 +1499,7 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
           return replaceInstUsesWith(I, X);
 
         // lshr (mul nuw (X, 2^N + 1)), N -> add nuw (X, lshr(X, N))
-        if (Op0->hasOneUse()) {
+        if (Op0->hasOneUse() && isGuaranteedNotToBeUndef(X, &AC, &I, &DT)) {
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nikic wrote:

We should do `if (!isGuaranteedNotToBeUndef) CreateFreeze` instead.

https://github.com/llvm/llvm-project/pull/96324