[llvm] [InstCombine] Explicitly set disjoint flag when converting xor to or. (PR #74229)

[Nikita Popov via llvm-commits]

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@@ -315,6 +315,7 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     if (DemandedMask.isSubsetOf(RHSKnown.Zero | LHSKnown.Zero)) {
       Instruction *Or =
           BinaryOperator::CreateOr(I->getOperand(0), I->getOperand(1));
+      cast<PossiblyDisjointInst>(Or)->setIsDisjoint(true);
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nikic wrote:

I don't think this is quite correct. This is only checking that the demanded bits are disjoint. If there is a conflict in the non-demanded bits, adding the `disjoint` flag is still going to make the result poison.

https://github.com/llvm/llvm-project/pull/74229