From: | Noah Misch <noah(at)leadboat(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Recent failures on buildfarm member hornet |
Date: | 2020-10-07 22:12:21 |
Message-ID: | 20201007221221.GC1498955@rfd.leadboat.com |
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Lists: | pgsql-hackers |
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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