From: Noah Misch <noah@leadboat.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Recent failures on buildfarm member hornet
Date: Wed, 7 Oct 2020 15:12:21 -0700
Message-ID: <20201007221221.GC1498955@rfd.leadboat.com> (raw)
In-Reply-To: <2398543.1602108196@sss.pgh.pa.us>
References: <1830491.1601944935@sss.pgh.pa.us>
<20201007014507.GB1422897@rfd.leadboat.com>
<2040113.1602035809@sss.pgh.pa.us>
<20201007021941.GD1422897@rfd.leadboat.com>
<2233910.1602090798@sss.pgh.pa.us>
<CAApHDvovu2O+SLerPK2fCqKKP-q6NWinzACvJkMQ9zZNEiCKJg@mail.gmail.com>
<20201007212056.GB1498955@rfd.leadboat.com>
<2397925.1602107299@sss.pgh.pa.us>
<2398543.1602108196@sss.pgh.pa.us>
On Wed, Oct 07, 2020 at 06:03:16PM -0400, Tom Lane wrote:
> I wrote:
> > I'm tempted to propose the attached small code rearrangement, which
> > might dissuade the compiler from thinking it can get away with this.
That patch does get hornet's -O2 build to again pass "make check". It doesn't
harm the code, so we may as well use it.
> > While I concur with your point that an old xlc version might not be
> > that exciting, there could be other compilers doing the same thing
> > in the future.
>
> After thinking about it a bit more, I'm not even convinced that what
> xlc seems to be doing is illegal per C spec. There are no sequence
> points within
>
> return list_make2(list_concat(directargs, orderedargs),
> makeInteger(ndirectargs));
There is, however, a sequence point between list_length(directargs) and
list_concat(), and the problem arises because xlc reorders those two. It's
true that makeInteger() could run before or after list_concat(), but that
alone would not have been a problem.
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To: pgsql-hackers@postgresql.org
Cc: noah@leadboat.com, tgl@sss.pgh.pa.us, dgrowleyml@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: Recent failures on buildfarm member hornet
In-Reply-To: <20201007221221.GC1498955@rfd.leadboat.com>
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