Re: Broken atomics code on PPC with FreeBSD 10.3

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Broken atomics code on PPC with FreeBSD 10.3
Date: 2016-12-30 16:14:24
Message-ID: 9E4EBC01-A299-4122-9416-32E5377253F8@anarazel.de
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On December 30, 2016 4:48:22 PM GMT+01:00, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>and got no warnings and the attached output. I'm not very good at
>reading
>PPC assembler, but I think what is happening in the "char" case is that
>gcc is trying to emulate a byte-wide operation using a word-wide one,
>ie an lwarx/stwcx. loop.

Hm. This seems to suggest a straight out code generation bug in that compiler, not a failure in intrinsic detection.

I'll note that there's certainly ppc64 machine with that intrinsic working (tested that on the community hydra during atomics development). So either it's a bug specific to some compiler version, or 32bit ppc.

I assume there's no trivial way to get a newer compiler on that machine?

Andres
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