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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/102698] omp atomic capture Abnormal results after
 running multiple times
Date: Tue, 12 Oct 2021 08:14:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102698

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Your testcase is racy and therefore anything can happen.
Please see
https://www.openmp.org/spec-html/5.1/openmpsu105.html#x138-1480002.19.7
"Only the read and write of the location designated by x are performed mutu=
ally
atomically. Neither the evaluation of expr or expr-list, nor the write to t=
he
location designated by v, need be atomic with respect to the read or write =
of
the location designated by x."
But the testcase is expecting that the store to o(idx(i), idy(i)) will be
atomic and done whenever the atomic or succeeds.  That is not the case, the
store is done after the atomic or succeeded, but using a normal store
instruction and other threads can store the same location in between (e.g. =
even
though they performed the atomic instruction later, they can store the resu=
lt
earlier).=