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