On Tue, Feb 21, 2017 at 3:49 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> 2017-02-21  Bin Cheng  <bin.cheng@arm.com>
>>
>> PR tree-optimization/77536
>> * tree-ssa-loop-manip.c (niter_for_unrolled_loop): New function.
>> (tree_transform_and_unroll_loop): Use above function to compute the
>> estimated niter of unrolled loop and use it when scaling profile.
>> * tree-ssa-loop-manip.h niter_for_unrolled_loop(): New declaration.
>> * tree-vect-loop.c (scale_profile_for_vect_loop): New function.
>> (vect_transform_loop): Call above function.
>>
>> gcc/testsuite/ChangeLog
>> 2017-02-21  Bin Cheng  <bin.cheng@arm.com>
>>
>> PR tree-optimization/77536
>> * gcc.dg/vect/pr79347.c: Revise testing string.
>> @@ -1329,7 +1339,12 @@ tree_transform_and_unroll_loop (struct loop *loop, unsigned factor,
>>    freq_h = loop->header->frequency;
>>    freq_e = EDGE_FREQUENCY (loop_preheader_edge (loop));
>>    if (freq_h != 0)
>> -    scale_loop_frequencies (loop, freq_e * (new_est_niter + 1), freq_h);
>> +    {
>> +      gcov_type scale;
>> +      /* This should not overflow.  */
>> +      scale = GCOV_COMPUTE_SCALE (freq_e * (new_est_niter + 1), freq_h);
>> +      scale_loop_frequencies (loop, scale, REG_BR_PROB_BASE);
>
> You need to use counts counts when new_est_niter is derrived from profile feedback.
> This is because frequencies are capped to 10000, so if loop iterates very many times,
> new_est_niter will be large, freq_h will be 10000 and freq_e will be 0.
>
> Also watch the case when freq_e==loop_preheader_edge (loop)->count==0 and freq_h
> is non-zero.  Just do MAX (freq_e, 1). This will not drop the loop body profile to 0.
>
>> +/* Scale profiling counters by estimation for LOOP which is vectorized
>> +   by factor VF.  */
>> +
>> +static void
>> +scale_profile_for_vect_loop (struct loop *loop, unsigned vf)
>> +{
>> +  edge preheader = loop_preheader_edge (loop);
>> +  unsigned freq_h = loop->header->frequency;
>> +  unsigned freq_e = EDGE_FREQUENCY (preheader);
>> +  /* Reduce loop iterations by the vectorization factor.  */
>> +  gcov_type new_est_niter = niter_for_unrolled_loop (loop, vf);
>> +
>> +  /* Use profiling count information if frequencies are zero.  */
>> +  if (freq_h == 0 || freq_e == 0)
>> +    {
>> +      freq_e = preheader->count;
>> +      freq_h = loop->header->count;
>> +    }
>> +
>> +  if (freq_h != 0)
>> +    {
>> +      gcov_type scale;
>> +      /* This should not overflow.  */
>> +      scale = GCOV_COMPUTE_SCALE (freq_e * (new_est_niter + 1), freq_h);
>> +      scale_loop_frequencies (loop, scale, REG_BR_PROB_BASE);
>> +    }
>
> Similarly here. Use counts when they are non-zero and use MAX (freq_e, 1).
> freq_e/freq_h needs to be gcov_type in that case.
>
> Patch is OK with these changes.  Thanks a lot!
Hi Honza,
There is the 3rd version patch fixing mentioned issues.  Is it OK?

Thanks,
bin