[PATCH] aarch64: Use target attributes to enable SVE in math functions

[Wilco Dijkstra]

Hi Adhemerval,

(adding Joe&Pierre)

> Instead of relying on global compiler flags ('-mcpu=generic+sve
> -march=armv8-a+sve') in the Makefile, this patch applies SVE
> architecture requirements directly at the function level.
>
> A new SVE_FUNCTION macro (mapping to
> __attribute__((target("+sve")))) and corresponding pragmas
> (OPTIONS_PUSH_SVE / OPTIONS_POP) are introduced in sv_math.h.
> These are then applied across all SVE-specific math implementations in
> sysdeps/aarch64/fpu/.

If we do this, it should be done in the AOR version first so we don't diverge
any further (and ideally the sources should be more identical).

Note AOR uses a single target attribute in the header (but then needs a
pop just for LLVM at the end of each file...).

> This allows building glibc with a -march without the need to
> also specify '+sve' (not an usual target, but it helps on testing
> some target without the need to rebuild the toolchain).

You can change CFLAGS to use -march= or -mcpu= and it will work. We use
a generic SVE target for the vector math functions - and that is fine since the
code is almost exclusively intrinsics. So I'd like to understand what goes wrong
if you change CFLAGS.

In principle we could scan CFLAGS for -mcpu=/-march= and add a +sve
rather than use a generic target, but that's QoI. I think the only difference it
would make is emitting RETAA in some helpers if PAC is enabled.

Cheers,
Wilco