[Bug target/80878] -mcx16 (enable 128 bit CAS) on x86_64 seems not to work on 7.1.0

[wuyongwei at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80878

--- Comment #28 from Yongwei Wu <wuyongwei at gmail dot com> ---
OK, somewhat answering myself. I was not aware of the fact that 128-bit atomic
read has to be implemented using cmpxchg16b as well, thus defeating some
non-CAS usage scenarios.

The natural question is: which usage scenario is more significant? Or is there
a way to support both?

I still think lock-free data structures are too import to ignore.