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

[Nikita Popov via llvm-commits]

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@@ -3012,7 +3012,7 @@ static Value *simplifyICmpWithConstant(CmpPredicate Pred, Value *LHS,
   }
 
   // Rule out tautological comparisons (eg., ult 0 or uge 0).
-  ConstantRange RHS_CR = ConstantRange::makeExactICmpRegion(Pred, *C);
+  ConstantRange RHS_CR = ConstantRange::makeAllowedICmpRegion(Pred, *C);
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nikic wrote:

Isn't makeAllowedICmpRegion semantically incorrect here? The following isEmptySet() check is correct for allowed region, but the isFullSet() check is only correct for the satisfying region, right? The current code is only correct if both are the same, which is the case for the exact region.

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