Re: [GOOGLE] tune loop scale factor for AutoFDO

[Dehao Chen <dehao at google dot com>]

As discussed offline, will commit this patch first, and think of other
smoothing algorithm to prevent profile insanity.

Dehao

On Fri, Nov 8, 2013 at 9:32 AM, Xinliang David Li <davidxl@google.com> wrote:
> 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);
>>      }