[Issue 20838] on modern (x86_64) CPUs, dmd emit cmpxchg8b instead of CMPXCHG16B

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20838

kinke <kinke at gmx.net> changed:

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                 CC|                            |kinke at gmx.net

--- Comment #6 from kinke <kinke at gmx.net> ---
(In reply to mw from comment #5)
> Want to file a bug against LDC ?

No need, cmpxchg16 is used for all x86_64 CPUs: https://d.godbolt.org/z/HesA24

For the few old CPUs not supporting it, it can be disabled via `-mattr=-cx16`
(but then it doesn't fall back to cmpxchg8 anway, so no idea how your results
came about).

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