[PATCH] x86: Optimize atomic_compare_and_exchange_[val|bool]_acq [BZ #28537]

[Andreas Schwab]

On Nov 03 2021, Arjan van de Ven via Libc-alpha wrote:

> What the patch does is check non-atomic first if the actual atomic operation has
> a chance of working. if it has a chance, the actual normal atomic operation is done as
> before. But if non-atomic read already tells you the cmpxchg has no chance to succeed, it errors
> out early.

But if the compiler keeps reusing the same cached value it may conclude
that the CAS _never_ has a chance to succeed.

Andreas.

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Andreas Schwab, schwab@linux-m68k.org
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