https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125354
--- Comment #7 from Andre Vehreschild <vehre at gcc dot gnu.org> --- I support the idea of activating `-fcoarray=single by` default to have the compiler accept all valid Fortran code w/o any additional options just because the user has some `num_images()` in its code. I do warn about using `-fcoarray=lib` (which `shared` implies), because this introduces an overhead in memory consumption. To be able to use derived types that have allocatable components in a coarray gfotran introduces a hidden component (of pointer size) for each allocatable or pointer component. Although `caf_shmem` does not make use of that component, `OpenCoarrays` does use it for its sub-windows (windows being an MPI term, here). Therefore do I consider `-fcoarray=single` as a reasonable default, but I vote against `shared`. When you want to further the use of `-fcoarray=shared`, consider to add it into the warning message that is issued when a user has coarray code in its code base, but no coarray-flag.
