https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81350
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- That said, I believe it is just a buggy testcase. In the 4 taskloop directives in apply_stencil I believe the rule for implicit data-sharing of W, A and B variables is: "In an orphaned task generating construct, if no default clause is present, dummy arguments are firstprivate." but of course, you actually rely on at least B to be shared and for efficiency it is desirable that W and A are also shared. Also, why so many taskwait directives everywhere? taskloop without nogroup clause will wait at the !$omp taskloop end until all those tasks finish.
