[Bug tree-optimization/128626] [14/15/16/17 Regression] wrong code at -O2/-O3: vectorizer ignores anti-dependence between int read and float store to malloc storage

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128626

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot 
gnu.org
   Last reconfirmed|                            |2026-11-12
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

  /* Even if we have an anti-dependence then, as the vectorized loop covers at
     least two scalar iterations, there is always also a true dependence.
     As the vectorizer does not re-order loads and stores we can ignore
     the anti-dependence if TBAA can disambiguate both DRs similar to the
     case with known negative distance anti-dependences (positive
     distance anti-dependences would violate TBAA constraints).  */
  if (((DR_IS_READ (dra) && DR_IS_WRITE (drb))
       || (DR_IS_WRITE (dra) && DR_IS_READ (drb)))
      && !alias_sets_conflict_p (get_alias_set (DR_REF (dra)),
                                 get_alias_set (DR_REF (drb))))
    return opt_result::success ();

is simply wrong for the positive-distance case (but OK for zero/negative
distance).