[CombToArith] Fix lowering of concat with single operand #6505
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A `comb.concat` operation with only a single operand would cause an `arith.extui` to be emitted with the same operand and result type. This trips the verifier of `extui`. Add a special case to that conversion to simply remove the `comb.concat` if it only has one operand. The canonicalizer would usually delete these degenerate concats, which is why we haven't seen this issue earlier. Also slightly tweak the lowering to produce a shift and or op for the least significant operand of the concat, which is already in the right spot.
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A
comb.concatoperation with only a single operand would cause anarith.extuito be emitted with the same operand and result type. This trips the verifier ofextui. Add a special case to that conversion to simply remove thecomb.concatif it only has one operand.The canonicalizer would usually delete these degenerate concats, which is why we haven't seen this issue earlier.
Also slightly tweak the lowering to produce a shift and or op for the least significant operand of the concat, which is already in the right spot.