From: Tom Lane <tgl@sss.pgh.pa.us>
To: Noah Misch <noah@leadboat.com>
cc: pgsql-hackers@lists.postgresql.org, David Rowley <dgrowleyml@gmail.com>
Subject: Re: Recent failures on buildfarm member hornet
In-reply-to: <20201007021941.GD1422897@rfd.leadboat.com>
References: <1830491.1601944935@sss.pgh.pa.us>
 <20201007014507.GB1422897@rfd.leadboat.com>
 <2040113.1602035809@sss.pgh.pa.us>
 <20201007021941.GD1422897@rfd.leadboat.com>
Comments: In-reply-to Noah Misch <noah@leadboat.com>
	message dated "Tue, 06 Oct 2020 19:19:41 -0700"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <2233909.1602090798.1@sss.pgh.pa.us>
Date: Wed, 07 Oct 2020 13:13:18 -0400
Message-ID: <2233910.1602090798@sss.pgh.pa.us>
Precedence: bulk

Noah Misch <noah@leadboat.com> writes:
> On Tue, Oct 06, 2020 at 09:56:49PM -0400, Tom Lane wrote:
>> Now that *is* surprising.  Could you poke a little further to determine
>> which module is getting miscompiled?  (gram.o seems like the next most
>> likely bet.)

> gram.o was it.  (The way I rebuilt gram.o also rebuilt parser.o and scan.o,
> but those seem far less likely.)

This suggests that the problem is misoptimization of gram.y's
makeOrderedSetArgs:

    /* don't merge into the next line, as list_concat changes directargs */
    ndirectargs = list_length(directargs);

    return list_make2(list_concat(directargs, orderedargs),
                      makeInteger(ndirectargs));

I think that if the compiler did what the comment says not to, it'd match
this symptom.  However, I'm baffled as to why our recent pg_list.h changes
would've affected that.

			regards, tom lane