[llvm] [SCEVExpander] Support hoisting udiv X, Y where Y is non-zero (PR #96102)

[Philip Reames via llvm-commits]

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@@ -1470,12 +1470,11 @@ Value *SCEVExpander::expand(const SCEV *S) {
 
   // We can move insertion point only if there is no div or rem operations
   // otherwise we are risky to move it over the check for zero denominator.
-  auto SafeToHoist = [](const SCEV *S) {
-    return !SCEVExprContains(S, [](const SCEV *S) {
+  auto SafeToHoist = [&](const SCEV *S) {
+    return !SCEVExprContains(S, [&](const SCEV *S) {
               if (const auto *D = dyn_cast<SCEVUDivExpr>(S)) {
-                if (const auto *SC = dyn_cast<SCEVConstant>(D->getRHS()))
-                  // Division by non-zero constants can be hoisted.
-                  return SC->getValue()->isZero();
+                if (SE.isKnownNonZero(D->getRHS()))
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preames wrote:

That is a great question.  I think we do.  We don't in a whole bunch of other cases, so this bug is not unique my new code, but yeah, I don't see any reason why hosting "udiv X, poison" above control flow would be legal.  

https://github.com/llvm/llvm-project/pull/96102