8-bit and 16-bit arithmetic

Ben Gamari ben at smart-cactus.org
Thu Oct 28 21:37:52 UTC 2021

Norman Ramsey <nr at cs.tufts.edu> writes:

> 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.


- Ben
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