On 20/04/2023 17:13, Richard Sandiford wrote:
"Andre Vieira (lists)" <andre.simoesdiasvie...@arm.com> writes:
On 20/04/2023 15:51, Richard Sandiford wrote:
"Andre Vieira (lists)" <andre.simoesdiasvie...@arm.com> writes:
Hi all,
This is a series of patches/RFCs to implement support in GCC to be able
to target AArch64's libmvec functions that will be/are being added to glibc.
We have chosen to use the omp pragma '#pragma omp declare variant ...'
with a simd construct as the way for glibc to inform GCC what functions
are available.
For example, if we would like to supply a vector version of the scalar
'cosf' we would have an include file with something like:
typedef __attribute__((__neon_vector_type__(4))) float __f32x4_t;
typedef __attribute__((__neon_vector_type__(2))) float __f32x2_t;
typedef __SVFloat32_t __sv_f32_t;
typedef __SVBool_t __sv_bool_t;
__f32x4_t _ZGVnN4v_cosf (__f32x4_t);
__f32x2_t _ZGVnN2v_cosf (__f32x2_t);
__sv_f32_t _ZGVsMxv_cosf (__sv_f32_t, __sv_bool_t);
#pragma omp declare variant(_ZGVnN4v_cosf) \
match(construct = {simd(notinbranch, simdlen(4))}, device =
{isa("simd")})
#pragma omp declare variant(_ZGVnN2v_cosf) \
match(construct = {simd(notinbranch, simdlen(2))}, device =
{isa("simd")})
#pragma omp declare variant(_ZGVsMxv_cosf) \
match(construct = {simd(inbranch)}, device = {isa("sve")})
extern float cosf (float);
The BETA ABI can be found in the vfabia64 subdir of
https://github.com/ARM-software/abi-aa/
This currently disagrees with how this patch series implements 'omp
declare simd' for SVE and I also do not see a need for the 'omp declare
variant' scalable extension constructs. I will make changes to the ABI
once we've finalized the co-design of the ABI and this implementation.
I don't see a good reason for dropping the extension("scalable").
The problem is that since the base spec requires a simdlen clause,
GCC should in general raise an error if simdlen is omitted.
Where can you find this in the specs? I tried to find it but couldn't.
Leaving out simdlen in a 'omp declare simd' I assume is OK, our vector
ABI defines behaviour for this. But I couldn't find what it meant for a
omp declare variant, obviously can't be the same as for declare simd, as
that is defined to mean 'define a set of clones' and only one clone can
be associated to a declare variant.
I was going from https://www.openmp.org/spec-html/5.0/openmpsu25.html ,
which says:
The simd trait can be further defined with properties that match the
clauses accepted by the declare simd directive with the same name and
semantics. The simd trait must define at least the simdlen property and
one of the inbranch or notinbranch properties.
(probably best to read it in the original -- it's almost incomprehensible
without markup)
I'm guessing the keyword here is 'trait' which I'm guessing is different
from a omp declare simd directive, which is why it's not required to
have a simdlen clause in an omp declare simd (see Jakub's comment).
But for declare variants I guess it does require you to? It doesn't
'break' anything, just means I need to add support for parsing the
extension clause as was originally planned.
Richard
