Re: [PATCH] rtl-optimization: ppc backend generates unnecessary signed extension.

[Hans-Peter Nilsson <hp@bitrange.com>]

On Fri, 24 Mar 2023, Peter Bergner via Gcc-patches wrote:

> On 3/23/23 6:12 PM, Jeff Law via Gcc-patches wrote:
> >>>> Is there a reason why REE cannot see that our (reg:QI 4) is a param register
> >>>> and thus due to our ABI, already correctly sign/zero extended?
> >>>
> >>> I don't think REE has ever considered exploiting ABI constraints. Handling
> >>> that might be a notable improvement on various targets.  It'd be a great
> >>> place to do some experimentation.
> >>
> >> Ok, so sounds like a good follow-on project after this patch is reviewed
> >> and committed (stage1).  Thanks for your input!
> >
> > Agreed.  I suspect that risc-v will benefit from such work as well. 
> > With that in mind, if y'all start poking at this, please loop in Raphael
> > (on cc) who's expressed an interest in this space.
> 
> Will do.  I suspect that it'll be best to come up with some generic interface
> using target hooks like "param regs are sign/zero extended" or "call return
> values are sign/zero extended", etc. that targets can conditionally opt into
> depending on their ABI that is in effect.

Pardon the arm-chair development mode but it sounds like 
re-inventing the TARGET_PROMOTE_* hooks...

Maybe just hook up TARGET_PROMOTE_FUNCTION_MODE to ree.c (as 
"you" already already define it for "rs6000")?

brgds, H-P