https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110712
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- this_2(D)->ap = VIEW_CONVERT_EXPR<struct [1]>(ap_3(D)); it looks odd since ap_3(D) is a is_gimple_reg but a struct[1] definitely would not. Maybe you are missing a dereference here? In C struct[1] would decay to a pointer so this.ap = ap; wouldn't work (besides that va_list copying requires va_copy).
