[PATCH V2] PING^ correct COUNT and PROB for unrolled loop

[Jiufu Guo <guojiufu@linux.ibm.com>]

Jiufu Guo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:

Hi,

I would like to reping this, hope to get approval for this patch.
https://gcc.gnu.org/legacy-ml/gcc-patches/2020-02/msg00927.html

BR,
Jiufu Guo

> Jiufu Guo <guojiufu@linux.ibm.com> writes:
>
> Hi,
>
> I'd like to ping this patch for trunk on stage 1.
>
> This patch could fix the issue on incorrect COUNT/FREQUENCES of loop
> unrolled blocks, and also could help the improve the cold/hot issue of
> the unrolled loops.
>
> patch is also at
> https://gcc.gnu.org/legacy-ml/gcc-patches/2020-02/msg00927.html
>
> Thanks,
> Jiufu
>
>> Jiufu Guo <guojiufu@linux.ibm.com> writes:
>>
>> Hi!
>>
>> I'd like to ping following patch. As near end of gcc10 stage 4, it seems
>> I would ask approval for GCC11 trunk.
>>
>> Thanks,
>> Jiufu Guo
>>
>>> Hi Honza and all,
>>>
>>> I updated the patch a little as below. Bootstrap and regtest are ok
>>> on powerpc64le.
>>>
>>> Is OK for trunk?
>>>
>>> Thanks for comments.
>>> Jiufu
>>>
>>> diff --git a/gcc/cfgloopmanip.c b/gcc/cfgloopmanip.c
>>> index 727e951..ded0046 100644
>>> --- a/gcc/cfgloopmanip.c
>>> +++ b/gcc/cfgloopmanip.c
>>> @@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
>>>  #include "gimplify-me.h"
>>>  #include "tree-ssa-loop-manip.h"
>>>  #include "dumpfile.h"
>>> +#include "cfgrtl.h"
>>>  
>>>  static void copy_loops_to (class loop **, int,
>>>  			   class loop *);
>>> @@ -1258,14 +1259,30 @@ duplicate_loop_to_header_edge (class loop *loop, edge e,
>>>  	  /* If original loop is executed COUNT_IN times, the unrolled
>>>  	     loop will account SCALE_MAIN_DEN times.  */
>>>  	  scale_main = count_in.probability_in (scale_main_den);
>>> +
>>> +	  /* If we are guessing at the number of iterations and count_in
>>> +	     becomes unrealistically small, reset probability.  */
>>> +	  if (!(count_in.reliable_p () || loop->any_estimate))
>>> +	    {
>>> +	      profile_count new_count_in = count_in.apply_probability (scale_main);
>>> +	      profile_count preheader_count = loop_preheader_edge (loop)->count ();
>>> +	      if (new_count_in.apply_scale (1, 10) < preheader_count)
>>> +		scale_main = profile_probability::likely ();
>>> +	    }
>>> +
>>>  	  scale_act = scale_main * prob_pass_main;
>>>  	}
>>>        else
>>>  	{
>>> +	  profile_count new_loop_count;
>>>  	  profile_count preheader_count = e->count ();
>>> -	  for (i = 0; i < ndupl; i++)
>>> -	    scale_main = scale_main * scale_step[i];
>>>  	  scale_act = preheader_count.probability_in (count_in);
>>> +	  /* Compute final preheader count after peeling NDUPL copies.  */
>>> +	  for (i = 0; i < ndupl; i++)
>>> +	    preheader_count = preheader_count.apply_probability (scale_step[i]);
>>> +	  /* Subtract out exit(s) from peeled copies.  */
>>> +	  new_loop_count = count_in - (e->count () - preheader_count);
>>> +	  scale_main = new_loop_count.probability_in (count_in);
>>>  	}
>>>      }
>>>  
>>> @@ -1381,6 +1398,38 @@ duplicate_loop_to_header_edge (class loop *loop, edge e,
>>>  	  scale_bbs_frequencies (new_bbs, n, scale_act);
>>>  	  scale_act = scale_act * scale_step[j];
>>>  	}
>>> +
>>> +      /* Need to update PROB of exit edge and corresponding COUNT.  */
>>> +      if (orig && is_latch && (!bitmap_bit_p (wont_exit, j + 1))
>>> +	  && bbs_to_scale)
>>> +	{
>>> +	  edge new_exit = new_spec_edges[SE_ORIG];
>>> +	  profile_count new_count_in = new_exit->src->count;
>>> +	  profile_count preheader_count = loop_preheader_edge (loop)->count ();
>>> +	  edge e;
>>> +	  edge_iterator ei;
>>> +
>>> +	  FOR_EACH_EDGE (e, ei, new_exit->src->succs)
>>> +	    if (e != new_exit)
>>> +	      break;
>>> +
>>> +	  gcc_assert (e && e != new_exit);
>>> +
>>> +	  new_exit->probability = preheader_count.probability_in (new_count_in);
>>> +	  e->probability = new_exit->probability.invert ();
>>> +
>>> +	  profile_count new_latch_count
>>> +	    = new_exit->src->count.apply_probability (e->probability);
>>> +	  profile_count old_latch_count = e->dest->count;
>>> +
>>> +	  EXECUTE_IF_SET_IN_BITMAP (bbs_to_scale, 0, i, bi)
>>> +	    scale_bbs_frequencies_profile_count (new_bbs + i, 1,
>>> +						 new_latch_count,
>>> +						 old_latch_count);
>>> +
>>> +	  if (current_ir_type () != IR_GIMPLE)
>>> +	    update_br_prob_note (e->src);
>>> +	}
>>>      }
>>>    free (new_bbs);
>>>    free (orig_loops);
>>> diff --git a/gcc/testsuite/gcc.dg/pr68212.c b/gcc/testsuite/gcc.dg/pr68212.c
>>> new file mode 100644
>>> index 0000000..f3b7c22
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.dg/pr68212.c
>>> @@ -0,0 +1,13 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fno-tree-vectorize -funroll-loops --param max-unroll-times=4 -fdump-rtl-alignments" } */
>>> +
>>> +void foo(long int *a, long int *b, long int n)
>>> +{
>>> +  long int i;
>>> +
>>> +  for (i = 0; i < n; i++)
>>> +    a[i] = *b;
>>> +}
>>> +
>>> +/* { dg-final { scan-rtl-dump-times "internal loop alignment added" 1 "alignments"} } */
>>> +