https://gcc.gnu.org/g:a1b67de3a4dc9ca745569a16c8cab33c0ee6ceca
commit r16-7735-ga1b67de3a4dc9ca745569a16c8cab33c0ee6ceca Author: Andre Vehreschild <[email protected]> Date: Thu Feb 12 11:13:25 2026 +0100 Fortran: Fix form team in caf_shmem [PR124071] Form team w/o new_index= tried to compute the new_index assuming that images are scattered onto to teams. I.e. the distribution is: Image index: 1 2 3 4 5 6 New team no: 1 2 1 2 1 2 , i.e. scattered But this algorithm failed, when the images were linearly distributed into the new teams, like in: Image index: 1 2 3 4 5 6 New team no: 1 1 1 2 2 2 The new approach is to look up a free index in the new team, when the computed one is already taken. Because F2018, 11.6.9, ยง4 states the new index is processor dependent, it feels safe to do it this way. PR fortran/124071 libgfortran/ChangeLog: * caf/shmem.c (_gfortran_caf_form_team): Take free index, when computed one is already taken. gcc/testsuite/ChangeLog: * gfortran.dg/coarray/form_team_1.f90: New test. Diff: --- gcc/testsuite/gfortran.dg/coarray/form_team_1.f90 | 18 +++++++++ libgfortran/caf/shmem.c | 45 ++++++++++++++++++----- 2 files changed, 53 insertions(+), 10 deletions(-) diff --git a/gcc/testsuite/gfortran.dg/coarray/form_team_1.f90 b/gcc/testsuite/gfortran.dg/coarray/form_team_1.f90 new file mode 100644 index 000000000000..e685efeb3780 --- /dev/null +++ b/gcc/testsuite/gfortran.dg/coarray/form_team_1.f90 @@ -0,0 +1,18 @@ +!{ dg-do run } + +program main + use, intrinsic :: iso_fortran_env, only: team_type + implicit none + type(team_type) :: team + integer :: slice_size, team_no + + if (num_images() >= 3) then + slice_size = num_images() / 3 + team_no = this_image() / slice_size + 1 + + form team (team_no, team) + + sync all + end if + +end program diff --git a/libgfortran/caf/shmem.c b/libgfortran/caf/shmem.c index 1ef36cde1ac8..9913db6d709a 100644 --- a/libgfortran/caf/shmem.c +++ b/libgfortran/caf/shmem.c @@ -1768,26 +1768,51 @@ _gfortran_caf_form_team (int team_no, caf_team_t *team, int *new_index, } else { - int im; - int exp = -1; + int im, cnt; + int exp; __atomic_fetch_add (&t->u.image_info->image_map_size, 1, __ATOMIC_SEQ_CST); sync_team (caf_current_team); - im = caf_current_team->index * t->u.image_info->image_map_size + cnt = t->u.image_info->image_map_size; + /* Try to map the source team's images linearly into the domain of the + new team. This works for scattered teams distributions. I.e. when a + set of images is distritubed in this way: + Image no: 1 2 3 4 5 6 + New team: 1 2 1 2 1 2 + but not for: + Image no: 1 2 3 4 5 6 + New team: 1 1 1 2 2 2 + */ + im = caf_current_team->index * cnt / caf_current_team->u.image_info->image_count.count; /* Map our old index into the domain of the new team's size. */ - if (__atomic_compare_exchange_n (&t->u.image_info->image_map[im], &exp, - this_image.image_num, false, - __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) - t->index = im; - else + do { - caf_internal_error (cannot_assign_index, stat, errmsg, errmsg_len); - return; + /* (Re-)set exp. */ + exp = -1; + if (__atomic_compare_exchange_n (&t->u.image_info->image_map[im], + &exp, this_image.image_num, false, + __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) + { + t->index = im; + goto form_team_finish; + } + /* Find a free new_index in the newly formed team for this image. + There no longer is any order to the teams. */ + ++im; + if (im >= t->u.image_info->image_map_size) + im = 0; + --cnt; } + while (cnt > 0); + + caf_internal_error (cannot_assign_index, stat, errmsg, errmsg_len); + return; } + +form_team_finish: sync_team (caf_current_team); caf_teams_formed = t;
