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Re: [patch] Fix node weight updates during ipa-cp (issue7812053)


On Wed, Mar 27, 2013 at 6:22 PM, Teresa Johnson <tejohnson@google.com> wrote:
> I found that the node weight updates on cloned nodes during ipa-cp were
> leading to incorrect/insane weights. Both the original and new node weight
> computations used truncating divides, leading to a loss of total node weight.
> I have fixed this by making both rounding integer divides.
>
> Bootstrapped and tested on x86-64-unknown-linux-gnu. Ok for trunk?

I'm sure we can outline a rounding integer divide inline function on
gcov_type.  To gcov-io.h, I suppose.

Otherwise this looks ok to me.

Thanks,
Richard.

> 2013-03-27  Teresa Johnson  <tejohnson@google.com>
>
>         * ipa-cp.c (update_profiling_info): Perform rounding integer
>         division when updating weights instead of truncating.
>         (update_specialized_profile): Ditto.
>
> Index: ipa-cp.c
> ===================================================================
> --- ipa-cp.c    (revision 197118)
> +++ ipa-cp.c    (working copy)
> @@ -2588,14 +2588,18 @@ update_profiling_info (struct cgraph_node *orig_no
>
>    for (cs = new_node->callees; cs ; cs = cs->next_callee)
>      if (cs->frequency)
> -      cs->count = cs->count * (new_sum * REG_BR_PROB_BASE
> -                              / orig_node_count) / REG_BR_PROB_BASE;
> +      cs->count = (cs->count
> +                   * ((new_sum * REG_BR_PROB_BASE + orig_node_count/2)
> +                      / orig_node_count)
> +                   + REG_BR_PROB_BASE/2) / REG_BR_PROB_BASE;
>      else
>        cs->count = 0;
>
>    for (cs = orig_node->callees; cs ; cs = cs->next_callee)
> -    cs->count = cs->count * (remainder * REG_BR_PROB_BASE
> -                            / orig_node_count) / REG_BR_PROB_BASE;
> +    cs->count = (cs->count
> +                 * ((remainder * REG_BR_PROB_BASE + orig_node_count/2)
> +                    / orig_node_count)
> +                 + REG_BR_PROB_BASE/2) / REG_BR_PROB_BASE;
>
>    if (dump_file)
>      dump_profile_updates (orig_node, new_node);
> @@ -2627,14 +2631,19 @@ update_specialized_profile (struct cgraph_node *ne
>
>    for (cs = new_node->callees; cs ; cs = cs->next_callee)
>      if (cs->frequency)
> -      cs->count += cs->count * redirected_sum / new_node_count;
> +      cs->count += (cs->count
> +                    * ((redirected_sum * REG_BR_PROB_BASE
> +                        + new_node_count/2) / new_node_count)
> +                    + REG_BR_PROB_BASE/2) / REG_BR_PROB_BASE;
>      else
>        cs->count = 0;
>
>    for (cs = orig_node->callees; cs ; cs = cs->next_callee)
>      {
> -      gcov_type dec = cs->count * (redirected_sum * REG_BR_PROB_BASE
> -                                  / orig_node_count) / REG_BR_PROB_BASE;
> +      gcov_type dec = (cs->count
> +                       * ((redirected_sum * REG_BR_PROB_BASE
> +                           + orig_node_count/2) / orig_node_count)
> +                       + REG_BR_PROB_BASE/2) / REG_BR_PROB_BASE;
>        if (dec < cs->count)
>         cs->count -= dec;
>        else
>
> --
> This patch is available for review at http://codereview.appspot.com/7812053


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