https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105011
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tom de Vries <vr...@gcc.gnu.org>: https://gcc.gnu.org/g:11fb784ac592567dbcb7874c27e67ee0feb8fbf0 commit r12-7799-g11fb784ac592567dbcb7874c27e67ee0feb8fbf0 Author: Tom de Vries <tdevr...@suse.de> Date: Wed Mar 23 16:37:45 2022 +0100 [libatomic] Fix return value in libat_test_and_set On nvptx (using a Quadro K2000 with driver 470.103.01) I ran into this: ... FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O1 execution test ... which mimimized to: ... #include <stdatomic.h> atomic_flag a = ATOMIC_FLAG_INIT; int main () { if ((atomic_flag_test_and_set) (&a)) __builtin_abort (); return 0; } ... The atomic_flag_test_and_set is implemented using __atomic_test_and_set_1, which corresponds to the "word-sized compare-and-swap loop" version of libat_test_and_set in libatomic/tas_n.c. The semantics of a test-and-set is that the return value is "true if and only if the previous contents were 'set'". But the code uses: ... return woldval != 0; ... which means it doesn't look only at the byte that was either set or not set, but at the entire word. Fix this by using instead: ... return (woldval & ((UTYPE) ~(UTYPE) 0 << shift)) != 0; ... Tested on nvptx. libatomic/ChangeLog: 2022-03-24 Tom de Vries <tdevr...@suse.de> PR target/105011 * tas_n.c (libat_test_and_set): Fix return value.