[Bug target/105011] [nvptx] FAIL: gcc.dg/atomic/stdatomic-flag-2.c -O1 execution test

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

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.