[llvm] [InstCombine] Do not keep samesign when speculatively executing icmps (PR #127007)

[Yingwei Zheng via llvm-commits]

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@@ -5636,6 +5636,11 @@ Instruction *InstCombinerImpl::foldICmpWithMinMax(Instruction &I,
       return false;
     return std::nullopt;
   };
+  // Remove samesign here since it is illegal to keep it when we speculatively
+  // execute comparisons. For example, `icmp samesign ult umax(X, -46), -32`
+  // cannot be decomposed into `(icmp samesign ult X, -46) or (icmp samesign ult
+  // -46, -32)`. `X` is allowed to be non-negative here.
+  Pred = static_cast<CmpInst::Predicate>(Pred);
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dtcxzyw wrote:

`samesign` flag is still needed before this line. We can avoid `isKnownNonNegative` queries if samesign is set.


https://github.com/llvm/llvm-project/pull/127007