[Bug target/86693] inefficient atomic_fetch_xor

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86693

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Hongtao.liu from comment #4)
> Change testcase a little bit, gcc now can generate lock btc
> 
> 
> void func1();
> 
> void func(unsigned long *counter)
> {
>         if (__atomic_fetch_xor(counter, 1, __ATOMIC_ACQ_REL) & 1) {
>                 func1();
>         }
> }
> 
> 
> func(unsigned long*):
>         lock btc        QWORD PTR [rdi], 0
>         jc      .L4
>         ret
> .L4:
>         jmp     func1()

We should rewrite the original test to the canonical form, similar to r12-5102.
Hongtao, can you do that?