8-bit and 16-bit arithmetic

On x86, GHC can translate 8-bit and 16-bit operations directly into the 8-bit and 16-bit machine instructions that the hardware supports. But there are other platforms on which the smallest unit of arithmetic may be 32 or even 64 bits. Is there a central module in GHC that can take care of rewriting 8-bit and 16-bit operations into 32-bit or 64-bit operations? Or is each back end on its own for this? (One of my students did some nice work on implementing this transformation with a minimal set of sign-extension and zero-extension operations: https://www.cs.tufts.edu/~nr/pubs/widen.pdf.) Norman