https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99840
--- Comment #5 from anlauf at gcc dot gnu.org --- OK, now I see it. gfc_get_shape does not init the resulting shape. The following simpler patch does the job: diff --git a/gcc/fortran/simplify.c b/gcc/fortran/simplify.c index 388aca7c38c..c27b47aa98f 100644 --- a/gcc/fortran/simplify.c +++ b/gcc/fortran/simplify.c @@ -8123,8 +8123,8 @@ gfc_simplify_transpose (gfc_expr *matrix) &matrix->where); result->rank = 2; result->shape = gfc_get_shape (result->rank); - mpz_set (result->shape[0], matrix->shape[1]); - mpz_set (result->shape[1], matrix->shape[0]); + mpz_init_set (result->shape[0], matrix->shape[1]); + mpz_init_set (result->shape[1], matrix->shape[0]); if (matrix->ts.type == BT_CHARACTER) result->ts.u.cl = matrix->ts.u.cl;