Re: [GOOGLE] tune loop scale factor for AutoFDO

[Xinliang David Li <davidxl at google dot com>]

On Fri, Nov 8, 2013 at 6:23 AM, Dehao Chen <dehao@google.com> wrote:
> AutoFDO sometimes has 0 profile in the loop's entry block because the
> debug info are lost and unrecoverable.

Is that a separate problem to track and fix?


Also is it better to do a round of loop profiling smoothing after auto
profile annotation to eliminate the insanity?

David


>
> E.g.
>
> if (a)
>   if (b)
>     for () {}
>
> This patch checks if the scale factor is 0, then use the normal scale.
>
> Bootstrapped and passed regression test and performance test.
>
> OK for google-4_8?
>
> Thanks,
> Dehao
>
> Index: gcc/cfgloopmanip.c
> ===================================================================
> --- gcc/cfgloopmanip.c (revision 204568)
> +++ gcc/cfgloopmanip.c (working copy)
> @@ -1262,6 +1262,8 @@ duplicate_loop_to_header_edge (struct loop *loop,
>   }
>        for (i = 0; i < ndupl; i++)
>   gcc_assert (scale_step[i] >= 0 && scale_step[i] <= REG_BR_PROB_BASE);
> +      if (flag_auto_profile && scale_main == 0)
> + scale_main = REG_BR_PROB_BASE;
>        gcc_assert (scale_main >= 0 && scale_main <= REG_BR_PROB_BASE
>     && scale_act >= 0  && scale_act <= REG_BR_PROB_BASE);
>      }