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From: Achim Gratz <Stromeko AT nexgo DOT de>
To: cygwin AT cygwin DOT com
Subject: Re: gcc and 128-bit compare/exchange
References: <ab69ca04-06a2-eeb9-4771-e37432b59a77 AT cs DOT umass DOT edu>
 <f27b324f-049c-7830-68cd-14813aab6eed AT cs DOT umass DOT edu>
 <66f51c13-4c87-3bd6-3b8e-01901155ef2a AT SystematicSw DOT ab DOT ca>
 <de26ff04-596e-1dad-f2ae-4b91ba53f5c1 AT cs DOT umass DOT edu>
 <0a2c77b2-7ff2-8118-8631-29d186184ad9 AT SystematicSw DOT ab DOT ca>
 <0fc8a150-99b1-34dc-0dfb-a096fc3b2096 AT cs DOT umass DOT edu>
Date: Wed, 11 Mar 2020 18:31:26 +0100
In-Reply-To: <0fc8a150-99b1-34dc-0dfb-a096fc3b2096@cs.umass.edu> (Eliot Moss's
 message of "Wed, 11 Mar 2020 02:13:40 -0400")
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Eliot Moss writes:
> What I am really reporting is that Cygwin is giving the pthread mutex form
> when it should not be.  My CPU clearly has the capability, and the compiler clearly
> knows how to emit the instruction, since the __sync form does it.  What is
> mysterious and tangled is why libatomic / libc are not delivering the desired
> version of the atomic compare-exchange function.

Assuming you want to use a library, it would have to detect this
capability at runtime (unless you force-build for a single CPU
architecture) and dispatch different code based on the result.  It's
probably the latter part that's missing on Cygwin.


Regards,
Achim.
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