https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112772
Bug ID: 112772 Summary: Some issues with OPTIONAL, ALLOCATABLE dummy arguments Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: fortran Assignee: unassigned at gcc dot gnu.org Reporter: anlauf at gcc dot gnu.org Target Milestone: --- While working on pr100651, the following issues surfaced (not discussed there): program main call test_rank1 () contains subroutine test_rank1 (msg1) class(*), optional, allocatable :: msg1(:) if (present (msg1)) stop 77 call assert_rank1 () ! <- no problem here call assert_rank1 (msg1) ! <- problematic code path end subroutine assert_rank1 (msg2) class(*), optional, allocatable :: msg2(:) end end This crashes at runtime. The dump for the problematic code path is: { struct __class__STAR_1_0a class.0; if (msg1 != 0B) { class.0._len = msg1->_len; class.0._data = msg1->_data; class.0._vptr = msg1->_vptr; } assert_rank1 (msg1 != 0B ? &class.0 : 0B); msg1->_data = class.0._data; msg1->_vptr = class.0._vptr; msg1->_len = class.0._len; } We need to protect the copy-out for an absent optional argument. Also, the testcase provided in https://gcc.gnu.org/pipermail/fortran/2023-November/059969.html which is similar to the above but uses deferred-length character shows a questionable tree dump (excerpt): void test_rank1 (struct array01_character(kind=1) * msg1, integer(kind=8) * _msg1) { integer(kind=8) D.4350; bitsizetype D.4351; sizetype D.4352; D.4350 = *_msg1; D.4351 = (bitsizetype) (sizetype) *_msg1 * 8; D.4352 = (sizetype) *_msg1; if (msg1 != 0B) { _gfortran_stop_numeric (77, 0); } L.2:; assert_rank1 (0B, &0); { struct array01_character(kind=1) * D.4348; integer(kind=8) * D.4349; D.4348 = msg1 != 0B ? msg1 : 0B; D.4349 = msg1 != 0B ? _msg1 : 0B; assert_rank1 (D.4348, D.4349); } } This emits warning messages with -fsanitize=undefined, likely due to the unconditional dereferencing of _msg1 at function entry.