On Thu, May 4, 2017 at 8:47 AM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> For the reasons explained in PR77536, niter_for_unrolled_loop assumes 5
> iterations in the absence of profiling information, although it doesn't
> increase beyond the estimate for the original loop. This left a hole in
> which the new estimate could be less than the old one but still greater
> than the limit imposed by CEIL (nb_iterations_upper_bound, unroll factor).
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Ok.
Thanks,
Richard.
> Thanks,
> Richard
>
>
> gcc/
> 2017-05-04 Richard Sandiford <richard.sandif...@linaro.org>
>
> * tree-ssa-loop-manip.c (niter_for_unrolled_loop): Add commentary
> to explain the use of truncating division. Cap the number of
> iterations to the maximum given by nb_iterations_upper_bound,
> if defined.
>
> gcc/testsuite/
> * gcc.dg/vect/vect-profile-1.c: New test.
>
> Index: gcc/tree-ssa-loop-manip.c
> ===================================================================
> --- gcc/tree-ssa-loop-manip.c 2017-05-03 08:46:26.068861808 +0100
> +++ gcc/tree-ssa-loop-manip.c 2017-05-04 07:41:56.686034705 +0100
> @@ -1104,6 +1104,9 @@ niter_for_unrolled_loop (struct loop *lo
> gcc_assert (factor != 0);
> bool profile_p = false;
> gcov_type est_niter = expected_loop_iterations_unbounded (loop,
> &profile_p);
> + /* Note that this is really CEIL (est_niter + 1, factor) - 1, where the
> + "+ 1" converts latch iterations to loop iterations and the "- 1"
> + converts back. */
> gcov_type new_est_niter = est_niter / factor;
>
> /* Without profile feedback, loops for which we do not know a better
> estimate
> @@ -1120,6 +1123,15 @@ niter_for_unrolled_loop (struct loop *lo
> new_est_niter = 5;
> }
>
> + if (loop->any_upper_bound)
> + {
> + /* As above, this is really CEIL (upper_bound + 1, factor) - 1. */
> + widest_int bound = wi::udiv_floor (loop->nb_iterations_upper_bound,
> + factor);
> + if (wi::ltu_p (bound, new_est_niter))
> + new_est_niter = bound.to_uhwi ();
> + }
> +
> return new_est_niter;
> }
>
> Index: gcc/testsuite/gcc.dg/vect/vect-profile-1.c
> ===================================================================
> --- /dev/null 2017-05-04 07:24:39.449302696 +0100
> +++ gcc/testsuite/gcc.dg/vect/vect-profile-1.c 2017-05-04 07:41:56.685075916
> +0100
> @@ -0,0 +1,35 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-additional-options "-fdump-tree-vect-details-blocks" } */
> +
> +/* At least one of these should correspond to a full vector. */
> +
> +void
> +f1 (int *x)
> +{
> + for (int j = 0; j < 2; ++j)
> + x[j] += 1;
> +}
> +
> +void
> +f2 (int *x)
> +{
> + for (int j = 0; j < 4; ++j)
> + x[j] += 1;
> +}
> +
> +void
> +f3 (int *x)
> +{
> + for (int j = 0; j < 8; ++j)
> + x[j] += 1;
> +}
> +
> +void
> +f4 (int *x)
> +{
> + for (int j = 0; j < 16; ++j)
> + x[j] += 1;
> +}
> +
> +/* { dg-final { scan-tree-dump {goto <bb [0-9]+>; \[0+.0*%\]} vect } } */
