> -----Original Message-----
> From: Richard Sandiford <richard.sandif...@arm.com>
> Sent: Monday, May 16, 2022 12:36 PM
> To: Tamar Christina <tamar.christ...@arm.com>
> Cc: gcc-patches@gcc.gnu.org; nd <n...@arm.com>; rguent...@suse.de;
> jeffreya...@gmail.com
> Subject: Re: [PATCH 1/3]middle-end: Add the ability to let the target decide
> the method of argument promotions.
>
> Tamar Christina <tamar.christ...@arm.com> writes:
> > Hi All,
> >
> > Some targets require function parameters to be promoted to a different
> > type on expand time because the target may not have native
> > instructions to work on such types. As an example the AArch64 port
> > does not have native instructions working on integer 8- or 16-bit
> > values. As such it promotes every parameter of these types to 32-bits.
>
> This doesn't seem specific to parameters though. It applies to any
> 8- or 16-bit variable. E.g.:
>
> #include <stdint.h>
> uint8_t foo(uint32_t x, uint32_t y) {
> uint8_t z = x != 0 ? x : y;
> return z + 1;
> }
>
> generates:
>
> foo:
> cmp w0, 0
> and w1, w1, 255
> and w0, w0, 255
> csel w0, w1, w0, eq
> add w0, w0, 1
> ret
>
> So I think the new behaviour is really a modification of the PROMOTE_MODE
> behaviour rather than the PROMOTE_FUNCTION_MODE behaviour.
>
> FWIW, I agree with Richard that it would be better not to add a new hook.
> I think we're really making PROMOTE_MODE choose between
> SIGN_EXTEND, ZERO_EXTEND or SUBREG (what LLVM would call “any
> extend”) rather than the current SIGN_EXTEND vs. ZERO_EXTEND choice.
Ah, I hadn't realized this also applied to locals.. ok I can modify
PROMOTE_MODE then,
but I also need the actual SSA_NAME and not just the type so will have to pass
this along.
From a practical point of view.. the actual hook however is implemented by 34
targets,
would I need to CC maintainers for each of them or would global maintainer
approval
suffice for these mostly mechanical changes?
Cheers,
Tamar
>
> Thanks,
> Richard
