[llvm] InstSimplify: teach simplifyICmpWithConstant about samesign (PR #125899)

[Ramkumar Ramachandra via llvm-commits]

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@@ -145,6 +145,14 @@ ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
   }
 }
 
+ConstantRange ConstantRange::makeAsymmetricICmpRegion(CmpPredicate Pred,
+                                                      const ConstantRange &CR) {
+  if (Pred.hasSameSign() && ICmpInst::isRelational(Pred))
+    return makeAllowedICmpRegion(Pred, CR).unionWith(makeAllowedICmpRegion(
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artagnon wrote:

I think `icmp samesign ult X, [2, 5)` should return the disjoint union of [0, 4) and [INT_MIN, -123). We have no way to represent a disjoint union as a ConstantRange, so I think we need a pair of ConstantRanges to check against? Not 100% sure, so would appreciate a sanity-check.

https://github.com/llvm/llvm-project/pull/125899