[Bug tree-optimization/100089] [11/12 Regression] 30% performance regression for denbench/mp2decoddata2 with -O3

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100089

--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> ---
So this fixes it for -fvect-cost-model=very-cheap.  One could argue that we
should enable the code for all cost models, fixing the -O3 regression (and
backportable to the branch).

I'll see to experiment with "fancy" costing of the stray vectorizations.  I'll
also note that the scanning for load/store (and other ifns not supported)
could be handled in the costing as well (but the costing would need to run
also for -fno-vect-cost-model then, just the result ignored if not forced).
I'm talking about

          bool require_loop_vectorize = false;
          for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
               !gsi_end_p (gsi); gsi_next (&gsi))
            {
              gimple *stmt = gsi_stmt (gsi);
              gcall *call = dyn_cast <gcall *> (stmt);
              if (call && gimple_call_internal_p (call))
                {
                  internal_fn ifn = gimple_call_internal_fn (call);
                  if (ifn == IFN_MASK_LOAD || ifn == IFN_MASK_STORE
                      /* Don't keep the if-converted parts when the ifn with
                         specifc type is not supported by the backend.  */
                      || (direct_internal_fn_p (ifn)
                          && !direct_internal_fn_supported_p
                          (call, OPTIMIZE_FOR_SPEED)))
                    {
                      require_loop_vectorize = true;
                      break;
                    }
                }