[llvm] [InstCombine] Fixing wrong select folding in vectors with undef elements (PR #102244)

[Nikita Popov via llvm-commits]

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@@ -1735,17 +1735,15 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
     APInt DemandedLHS(DemandedElts), DemandedRHS(DemandedElts);
     if (auto *CV = dyn_cast<ConstantVector>(Sel->getCondition())) {
       for (unsigned i = 0; i < VWidth; i++) {
-        // isNullValue() always returns false when called on a ConstantExpr.
-        // Skip constant expressions to avoid propagating incorrect information.
         Constant *CElt = CV->getAggregateElement(i);
-        if (isa<ConstantExpr>(CElt))
-          continue;
+
         // TODO: If a select condition element is undef, we can demand from
         // either side. If one side is known undef, choosing that side would
         // propagate undef.
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nikic wrote:

I'd drop this TODO as well.

If we wanted to handle something here it would be poison, in which case we could clear the bit in both vectors.

https://github.com/llvm/llvm-project/pull/102244