I think we need to add MemoryEffects DXIL canonicalization to translate from attribute values with more nuance to conservative versions for DXIL serialization - see comment on DXILPrepare.cpp. Otherwise, we could have duplicate attribute sets once these are translated in DXILBitcodeWriter, which would result in bitcode differences between equivalent DXIL IR. In other words, if you round-trip the DXIL output from here, the bitcode would change.

I don't see why we would want a different behavior here between ABI and preferred alignments.