[InstCombine] Simplify select using KnownBits of condition (#95923) Simplify the arms of a select based on the KnownBits implied by its condition. For now this only handles the case where the select arm folds to a constant, but this can be generalized to handle other patterns by using SimplifyDemandedBits instead (in that case we would also have to limit to non-undef conditions). This is implemented by adding a new member to SimplifyQuery that can be used to inject an additional condition. The affected values are pre-computed and we don't call computeKnownBits() if the select arms don't contain affected values. This reduces the cost in some pathological cases.
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