[Bug target/105162] New: [AArch64] outline-atomics drops dmb ish barrier on __sync builtins

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105162

            Bug ID: 105162
           Summary: [AArch64] outline-atomics drops dmb ish barrier on
                    __sync builtins
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: spop at gcc dot gnu.org
  Target Milestone: ---

With -mno-outline-atomics gcc produces a `dmb ish` barrier on __sync builtins
as required by the Intel specification 
(see fix for https://gcc.gnu.org/PR65697 
https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=f70fb3b635f9618c6d2ee3848ba836914f7951c2
https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=ab876106eb689947cdd8203f8ecc6e8ac38bf5ba
)

$ cat a.c
int foo(int a)
{
  return __sync_bool_compare_and_swap(&a, 4, 5);
}
$ gcc -O2 a.c -S -o- -mno-outline-atomics 
foo:
        sub     sp, sp, #16
        mov     w1, 5
        str     w0, [sp, 12]
        add     x0, sp, 12
.L4:
        ldxr    w2, [x0]
        cmp     w2, 4
        bne     .L5
        stlxr   w3, w1, [x0]
        cbnz    w3, .L4
.L5:
        dmb     ish
        cset    w0, eq
        add     sp, sp, 16
        ret

With -moutline-atomics gcc does not generate the barrier:

$ gcc -O2 a.c -S -o-  -moutline-atomics 
foo:
        stp     x29, x30, [sp, -32]!
        mov     w1, 5
        mov     x29, sp
        add     x2, sp, 28
        str     w0, [sp, 28]
        mov     w0, 4
        bl      __aarch64_cas4_acq_rel
        cmp     w0, 4
        cset    w0, eq
        ldp     x29, x30, [sp], 32
        ret

Happens on gcc-8, 9, 10, 11, and trunk.