Re: BUG #15121: Multiple UBSAN errors

Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On 03/19/2018 03:28 PM, Martin Liška wrote:
>>>> Note that building postgresql with -03, I see some array tests failing.

> 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] = '{"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] = '{"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