From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
cc: =?UTF-8?Q?Martin_Li=c5=a1ka?= <marxin.liska@gmail.com>,
        pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #15121: Multiple UBSAN errors
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Comments: In-reply-to Tomas Vondra <tomas.vondra@2ndquadrant.com>
	message dated "Mon, 19 Mar 2018 19:07:49 +0100"
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Date: Mon, 19 Mar 2018 14:20:33 -0400
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Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On 03/19/2018 03:28 PM, Martin Li=C5=A1ka wrote:
>>>> Note that building postgresql with -03, I see some array tests failin=
g.

> I'm getting failures in errors, union and alter_table, but none of those
> are related to arrays. So, which tests are failing for you and how do
> the failures look like?

I tried -O3 with gcc 7.3.1 (Fedora 26), and that passes check-world
just fine.  Then I tried -O3 with gcc 8.0.1 (prerelease Fedora 28),
and indeed that's got some problems.  It looks like array_out fails
for multidimensional arrays, because all the diffs look about
like this one:

*** 106,116 ****
    SET c[2:2] =3D '{"new_word"}'                                         =
                                                                  =

    WHERE array_dims(c) is not null;                                      =
                                                                =

  SELECT a,b,c FROM arrtest;                                              =
                                                                =

!        a       |           b           |         c                      =
                                                                =

! ---------------+-----------------------+-------------------             =
                                                                =

!  {16,25,3,4,5} | {{{113,142},{1,147}}} | {}                             =
                                                                =

!  {}            | {3,4}                 | {foo,new_word}                 =
                                                                =

!  {16,25,23}    | {{3,4},{4,5}}         | {foobar,new_word}              =
                                                                =

  (3 rows)                                                                =
                                                                =

                                                                          =
                                                                =

  SELECT a[1:3],                                                          =
                                                                =

--- 106,116 ----
    SET c[2:2] =3D '{"new_word"}'                                         =
                                                                  =

    WHERE array_dims(c) is not null;                                      =
                                                                =

  SELECT a,b,c FROM arrtest;                                              =
                                                                =

!        a       |       b       |         c                              =
                                                                =

! ---------------+---------------+-------------------                     =
                                                                =

!  {16,25,3,4,5} | {{            | {}                                     =
                                                                =

!  {}            | {3,4}         | {foo,new_word}                         =
                                                                =

!  {16,25,23}    | {{3,4},{4,5}} | {foobar,new_word}                      =
                                                                =

  (3 rows)                                                                =
                                                                =

                                                                          =
                                                                =

  SELECT a[1:3],                                                          =
                                                                =


Note that 1-D and 2-D arrays print fine, it's only 3-D or deeper
that print wrong.  Very odd.  Maybe it's bad code on our part,
but I think the odds are at least as good that it's a new gcc bug.

			regards, tom lane