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Re: About machine description for atomic_exchange

From: Andrew Haley <aph at redhat dot com>
To: William Tambe <tambewilliam at gmail dot com>, Oleg Endo <oleg dot endo at t-online dot de>
Cc: gcc-help <gcc-help at gcc dot gnu dot org>
Date: Fri, 13 Sep 2019 09:15:16 +0100
Subject: Re: About machine description for atomic_exchange
References: <CAF8i9mM5cWGgRO-x9g-5YcgKrgYvhyrJ6g4-uPaHiGepyNjLZQ@mail.gmail.com> <cab5b4e7d4a6a3c43b8ea9e90459b7e3295729c0.camel@t-online.de> <CAF8i9mOsN3sXWJyeTWgzZqxeiCV_kpaHRcN7S1LLTm9_-eDasA@mail.gmail.com>

On 9/12/19 4:04 PM, William Tambe wrote:
> Is there an example, not necessarily for atomic_exchange, that I can follow ?
> 
> Also, is this behavior related to GCC memory model ? ie:
> (MEM_VOLATILE_P (operands[1])) for atomic_exchange always TRUE
> regardless of whether the memory operand was declared using
> "volatile"

I've been thinking about this, and have been unable to come up with a
use for a non-volatile atomic_exchange. If you had such a thing you'd
also have undefined behaviour if an other thread accessed the operand
racily.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671

References:
- About machine description for atomic_exchange
  - From: William Tambe
- Re: About machine description for atomic_exchange
  - From: Oleg Endo
- Re: About machine description for atomic_exchange
  - From: William Tambe

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