Re-apply reverted niter change 1/4

[Bin.Cheng]

On Mon, Apr 18, 2016 at 6:24 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
> Hi,
> as discussed on IRC today, I would like to re-apply the patch to fix bogus
> realistic bounds in niter.  As it turned out, we seem to rely on this bogus
> estimate in few benchmarks and there is miscompilation with avx512.
>
> The performance regressions should be solved my planned patch to introduce
> likely upper bounds - here we can track the assumption that there are no
> trailing arrays in the structures. I plan to send it after some benchmarking.
>
> Moreover we can get smarter about tracking trailing arrays.  We seem to get
> wrong MEM_REFs (as noticed by Richard), we may disable the path for non-C
> based languages (regresions are for Fortran testcases) and we can track object
> sizes.
>
> I plan to do that step-by-step so possible additional fallout is easier to
> track.  This patch re-instantiate first fix included in the orignial
> patch - ivopts should consider max_stmt-executions_int when giving an estimate
> on number of iterations.
>
> Bootstrapped/regtested x86_64-linux, comitted.
>
> Honza
>
> Index: ChangeLog
> ===================================================================
> --- ChangeLog   (revision 235157)
> +++ ChangeLog   (working copy)
> @@ -1,3 +1,8 @@
> +2016-04-17  Jan Hubicka  <jh@suse.cz>
> +
> +       * tree-ssa-loop-ivopts.c (avg_loop_niter): Use also
> +       max_loop_iterations_int.
> +
>  2016-04-18  Richard Biener  <rguenther@suse.de>
>
>         PR tree-optimization/43434
> Index: tree-ssa-loop-ivopts.c
> ===================================================================
> --- tree-ssa-loop-ivopts.c      (revision 235064)
> +++ tree-ssa-loop-ivopts.c      (working copy)
> @@ -121,7 +121,11 @@ avg_loop_niter (struct loop *loop)
>  {
>    HOST_WIDE_INT niter = estimated_stmt_executions_int (loop);
>    if (niter == -1)
> -    return AVG_LOOP_NITER (loop);
> +    {
> +      niter = max_stmt_executions_int (loop);
> +      if (niter == -1 || niter > AVG_LOOP_NITER (loop))
> +        return AVG_LOOP_NITER (loop);
Any reason why AVG_LOOP_NITER is still used if niter gives larger number?

Thanks,
bin
> +    }
>
>    return niter;
>  }