[Bug tree-optimization/118727] [15 Regression] gcc.dg/pr108692.c fails on LoongArch

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118727

--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
line 1408, tree-vect-patterns.cc:

      if (gimple_call_internal_fn (abd_stmt) == IFN_ABD)
        {    
          if (!vect_look_through_possible_promotion (vinfo, abd_oprnd0,
                                                     &unprom[0])
              || !vect_look_through_possible_promotion (vinfo, abd_oprnd1,
                                                        &unprom[1]))
            return NULL;
        }    

it seems suspicious: the sign of ABD operands matters so we cannot let
vect_look_through_possible_promotion strip away the sign changes.