Norman Ramsey
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.)
As Carter indicated, this is currently done on a per-backend basis. This could indeed probably be consolidated, although we would want to make sure that in so doing we do not leave easy money on the table: It seems plausible to me that the backend may be able to generate better code than a naive lowering to wide arithmetic might otherwise generate. Cheers, - Ben