[Bug target/107713] Wrong implementation atomic_exchange<short> on LoongArch

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107713

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by LuluCheng <chenglulu@gcc.gnu.org>:

https://gcc.gnu.org/g:f0024bfb228f94e60e06dc32a4983e40a9b90be5

commit r13-4136-gf0024bfb228f94e60e06dc32a4983e40a9b90be5
Author: Jinyang He <hejinyang@loongson.cn>
Date:   Thu Nov 17 14:38:52 2022 +0800

    LoongArch: Fix atomic_exchange expanding [PR107713]

    We used to expand atomic_exchange_n(ptr, new, mem_order) for subword types
    into something like:

        {
          __typeof__(*ptr) t = atomic_load_n(ptr, mem_order);
          atomic_compare_exchange_n(ptr, &t, new, true, mem_order, mem_order);
          return t;
        }

    It's incorrect because another thread may store a different value into *ptr
    after atomic_load_n.  Then atomic_compare_exchange_n will not store into
    *ptr, but atomic_exchange_n should always perform the store.

    gcc/ChangeLog:

            PR target/107713
            * config/loongarch/sync.md
            (atomic_cas_value_exchange_7_<mode>): New define_insn.
            (atomic_exchange): Use atomic_cas_value_exchange_7_si instead of
            atomic_cas_value_cmp_and_7_si.

    gcc/testsuite/ChangeLog:

            PR target/107713
            * gcc.target/loongarch/pr107713-1.c: New test.
            * gcc.target/loongarch/pr107713-2.c: New test.