Re: [Patch] libgomp: Fix reverse-offload for GOMP_MAP_TO_PSET

[Thomas Schwinge <thomas@codesourcery.com>]

Hi Tobias!

On 2023-02-06T12:52:11+0100, Tobias Burnus <tobias@codesourcery.com> wrote:
> Seems as if I missed a GOMP_MAP_TO_PSET issue before. As nvptx is
> XFAILed before, I only found it when testing on AMDGCN.
>
> For an array-descriptor 'ai' variable, omplower has:
>    map(tofrom:MEM <integer(kind=4)[0:]> [(integer(kind=4)[0:] *)D.4346] [len: D.4345])
>    map(to:ai [pointer set, len: 64])
>    map(alloc:ai.data [pointer assign, bias: 0])
>
> The latter reaches GCC with the same address as 'ai' – i.e. the
> one of the array descriptor. This then needs to be dereferenced
> to get the address of the actual pointer.
> The patch assumes (and asserts) that 'ai.data' is part of the 'ai'
> such that I can use the host address of 'ai' to access the data.
> If that's not guaranteed, we have to find another way (e.g. another
> lookup). But so far it seems to hold and I have not seen a bias
> other than 0.
>
> With that patch, libgomp.fortran/reverse-offload-5.f90 now works
> with AMDGCN.

Confirming the latter, thanks.  (..., but I've not actually reviewed the
code changes.)

> OK? Any comments to the attached patch?

Yes:

> libgomp: Fix reverse-offload for GOMP_MAP_TO_PSET
>
> libgomp/
>       * target.c (gomp_target_rev): Dereference ptr
>       to get device address.
>       * libgomp.fortran/reverse-offload-5.f90: Add test
>       for unallocated allocatable.
>
>  libgomp/target.c                                        | 7 ++++++-
>  libgomp/testsuite/libgomp.fortran/reverse-offload-5.f90 | 6 ++++--
>  2 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/libgomp/target.c b/libgomp/target.c
> index c1682caea13..5cdd845291a 100644
> --- a/libgomp/target.c
> +++ b/libgomp/target.c
> @@ -3579,8 +3579,13 @@ gomp_target_rev (uint64_t fn_ptr, uint64_t mapnum, uint64_t devaddrs_ptr,
>                     }
>                   int k;
>                   n2 = NULL;
> -                 cdata[i].present = true;
> +                 /* Dereference devaddrs[j] to get the device addr.  */
> +                 assert (devaddrs[j]-sizes[j] == cdata[i].devaddr);
> +                 devaddrs[j] = *(uint64_t *) (devaddrs[i] + sizes[j]);

For x86_64-pc-linux-gnu '-m32' multilib:

    [...]
    [...]/source-gcc/libgomp/target.c: In function ‘gomp_target_rev’:
    [...]/source-gcc/libgomp/target.c:3615:36: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
     3615 |                     devaddrs[j] = *(uint64_t *) (devaddrs[i] + sizes[j]);
          |                                    ^
    cc1: all warnings being treated as errors
    make[9]: *** [target.lo] Error 1
    make[9]: Leaving directory `[...]/build-gcc/x86_64-pc-linux-gnu/32/libgomp'
    [...]

I suppose you'd do similar to what you already have a few lines above;
that is, cast through 'uintptr_t':

    devaddrs[j] = *(uint64_t *) (uintptr_t) (devaddrs[i] + sizes[j]);


Grüße
 Thomas


> +                 cdata[j].present = true;
>                   cdata[j].devaddr = devaddrs[j];
> +                 if (devaddrs[j] == 0)
> +                   continue;
>                   k = gomp_map_cdata_lookup (cdata, devaddrs, kinds, sizes, j,
>                                              devaddrs[j],
>                                              devaddrs[j] + sizeof (void*),
> diff --git a/libgomp/testsuite/libgomp.fortran/reverse-offload-5.f90 b/libgomp/testsuite/libgomp.fortran/reverse-offload-5.f90
> index ef7eb7bdd52..16810eb47de 100644
> --- a/libgomp/testsuite/libgomp.fortran/reverse-offload-5.f90
> +++ b/libgomp/testsuite/libgomp.fortran/reverse-offload-5.f90
> @@ -24,7 +24,7 @@ s2 = 55
>
>  !$omp target map(to: A, A2, s1, s2)
>  block
> -  integer, allocatable :: ai(:), ai2(:), si1, si2
> +  integer, allocatable :: ai(:), ai2(:), ai3(:), si1, si2, si3
>
>    a = a * 2
>    a2 = a2 * 3
> @@ -38,7 +38,7 @@ block
>
>    !$omp target device (ancestor:1)  &
>    !$omp&       map(to: A, s1, ai, si1) map(always, to: a2, s2)  &
> -  !$omp&       map(tofrom: ai2, si2)
> +  !$omp&       map(tofrom: ai2, si2, ai3, si3)
>      if (shared_mem) then
>        if (any (a  /= 2 * [1,2,3,4])) stop 1
>        if (s1 /= 4 * 532) stop 2
> @@ -52,6 +52,7 @@ block
>      if (any (ai2 /= [8,4,7,1])) stop 8
>      if (si1 /= 64) stop 9
>      if (si2 /= 765) stop 10
> +    if (allocated (ai3) .or. allocated(si3)) stop 26
>
>      a = a*3
>      a2 = a2*7
> @@ -80,6 +81,7 @@ block
>    endif
>    if (any (ai2 /= 21 * [8,4,7,1])) stop 24
>    if (si2 /= 31 * 765) stop 25
> +  if (allocated (ai3) .or. allocated(si3)) stop 27
>
>    deallocate (ai, ai2, si1, si2)
>  end block
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