[llvm] [LV] Rewrite UDiv A, B -> UDiv A, UMax(B, 1) in trip counts if needed. (PR #92177)

[Florian Hahn via llvm-commits]

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@@ -4304,12 +4304,22 @@ ScalarEvolution::getSequentialMinMaxExpr(SCEVTypes Kind,
   }
 
   for (unsigned i = 1, e = Ops.size(); i != e; ++i) {
+    bool MayBeUB = SCEVExprContains(Ops[i], [this](const SCEV *S) {
+      auto *UDiv = dyn_cast<SCEVUDivExpr>(S);
+      // The UDiv may be UB if the divisor is poison or zero. Unless the divisor
+      // is a non-zero constant, we have to assume the UDiv may be UB.
+      return UDiv && (!isa<SCEVConstant>(UDiv->getOperand(1)) ||
+                      !isKnownNonZero(UDiv->getOperand(1)));
+    });
+
+    if (MayBeUB)
+      continue;
     // We can replace %x umin_seq %y with %x umin %y if either:
     //  * %y being poison implies %x is also poison.
     //  * %x cannot be the saturating value (e.g. zero for umin).
     if (::impliesPoison(Ops[i], Ops[i - 1]) ||
-        isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_NE, Ops[i - 1],
-                                        SaturationPoint)) {
+        (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_NE, Ops[i - 1],
+                                         SaturationPoint))) {
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fhahn wrote:

Left over change, removed, thanks!

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