Re: [PATCH] OpenMP front-end: allow requires dynamic_allocators

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Dec 20, 2021 at 03:16:23PM +0000, Andrew Stubbs wrote:
> This patch removes the "sorry" message for the OpenMP "requires
> dynamic_allocators" feature in C, C++ and Fortran.
> 
> The clause is supposed to state that the user code will not work without the
> omp_alloc/omp_free and omp_init_allocator/omp_destroy_allocator and these
> things *are* present, so there should be no problem allowing it.
> 
> I can't see any reason for our implementation to *do* anything with this
> statement -- it's fine for the allocators to work the same with or without
> it.

Well, we should do a lot with it, but that can wait for later.
In particular, if OMP_REQUIRES_DYNAMIC_ALLOCATORS is not present,
we should be rejecting omp_init_allocator and omp_destroy_allocator
in target regions (maybe just a warning though), and for allocate clauses,
directives, and the omp_alloc etc. APIs we should in the target region
enforce they don't use omp_null_allocator and the allocators they use
is mentioned in uses_allocators (and implement uses_allocators).
But, right now it is unclear to me how exactly is that supposed to work
with declare target to routines, those aren't nested inside of the target
and so can't know what uses_allocator is used, so they can't make any
allocations?  Or is it just that we can't diagnose this in such routines
and only can diagnose omp_null_allocator isn't used...
> 
> I think this patch ought to be fine for GCC 12, but if not it can wait until
> stage 1 opens. I shall backport this to OG11 shortly.

Anyway, your patch is a step forward, as we don't support uses_allocators,
the non-requires dynamic_allocators way is unusable for any target region
allocations due to that and so requires dynamic_allocators is the only thing
we actually support, but we were rejecting that directive...

Ok and sorry for the delay.

> gcc/c/ChangeLog:
> 
> 	* c-parser.c (c_parser_omp_requires): Don't "sorry" dynamic_allocators.
> 
> gcc/cp/ChangeLog:
> 
> 	* parser.c (cp_parser_omp_requires): Don't "sorry" dynamic_allocators.
> 
> gcc/fortran/ChangeLog:
> 
> 	* openmp.c (gfc_match_omp_requires): Don't "sorry" dynamic_allocators.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gfortran.dg/gomp/requires-8.f90: Reinstate dynamic allocators
> 	requirement.

	Jakub