Re: [patch] Fix loop bound comparison in the vectorizer

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 9/11/07, Ira Rosen <IRAR@il.ibm.com> wrote:
>
> This part of the x86 vect cost model patch
>
> 2007-09-10  Harsha Jagasia <harsha.jagasia@amd.com>
>             Jan Sjodin <jan.sjodin@amd.com>
>
>         * tree-vect-analyze.c (vect_analyze_operations): Change
>         comparison of loop iterations with threshold to less than
>         or equal to instead of less than. Reduce
>         min_scalar_loop_bound by one.
>
> makes the threshold negative in the default case where
> PARAM_MIN_VECT_LOOP_BOUND is 0.
>
>   min_scalar_loop_bound = ((PARAM_VALUE (PARAM_MIN_VECT_LOOP_BOUND)
>                             * vectorization_factor) - 1);
> ...
>   th = (unsigned) min_scalar_loop_bound;
> ...
>
> and this makes the following condition always true (at least on
> x86_64-linux):
>
>   if (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
>       && LOOP_VINFO_INT_NITERS (loop_vinfo) <= th)
>     {
>       if (vect_print_dump_info (REPORT_UNVECTORIZED_LOOPS))
>         fprintf (vect_dump, "not vectorized: vectorization not "
>                  "profitable.");
> ...
>       return false;
>     }
>
> and no loop can get vectorized now.
>
> I suggest to change the default and the minimum value of
> PARAM_MIN_VECT_LOOP_BOUND to 1. In addition to fixing the above problem, it
> seems reasonable to vectorize loops with at least one iteration.
>
> Bootstrapping with vectorization enabled and testing on x86_64-linux . O.K.
> for mainline once the testing completes?

Yes, this is reasonable.

Thanks,
Richard.

> Thanks,
> Ira
>
> ChangeLog:
>
>       * params.def (PARAM_MIN_VECT_LOOP_BOUND): Change default and minimum
> to 1.
>
> Index: params.def
> ===================================================================
> --- params.def  (revision 128363)
> +++ params.def  (working copy)
> @@ -148,7 +148,7 @@ DEFPARAM (PARAM_MAX_VARIABLE_EXPANSIONS,
>  DEFPARAM (PARAM_MIN_VECT_LOOP_BOUND,
>           "min-vect-loop-bound",
>           "If -ftree-vectorize is used, the minimal loop bound of a loop to
> be considered for vectorization",
> -         0, 0, 0)
> +         1, 1, 0)
>
>  /* The maximum number of instructions to consider when looking for an
>     instruction to fill a delay slot.  If more than this arbitrary
>
>