I think carter has it still right that it happens in the backends.

If a new backend doesn't support these we could move this up into Cmm though without much issue I think.

I think thats done on a per backend basis (though theres been a lot of changes since i last looked at some of the relevent pieces). (i'm actually based in Cambridge MA for the next 1-2 years if you wanna brain storm IRL sometime)

On Thu, Oct 28, 2021 at 4:59 PM Norman Ramsey <nr@cs.tufts.edu> wrote:

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
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