Re: [GOOGLE] Refactor the profile propagation for AutoFDO

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

In this case the backedge will be a critical edge, which will be split by GCC.

David

On Mon, Nov 25, 2013 at 10:08 AM, Diego Novillo <dnovillo@google.com> wrote:
> Thanks, Deaho.
>
> One other thing that I've found on the LLVM implementation (that I'm
> not sure happens in GCC): self-referential edges.  If a loop consists
> of a single-basic block, the back edge will point to itself.  I
> haven't been able to reproduce it with regular control flow constructs
> in GCC.
>
> When this happens, and if we've visited the block itself already
> (i.e., the block has weights), I've simply set the weight of the
> self-referential edge to the weight of the block itself.  Do you see
> any problems with that heuristic?
>
>
> Thanks.  Diego.
>
> On Mon, Nov 25, 2013 at 12:56 PM, Dehao Chen <dehao@google.com> wrote:
>> afdo_propagate_multi_edge can do everything afdo_propagate_single_edge
>> does. So we refactor the code to keep only one afdo_propagate_edge
>> function.
>>
>> Bootstrapped and passed all unittests and performance tests.
>>
>> OK for googlge branch?
>>
>> Thanks,
>> Dehao
>>
>> Index: gcc/auto-profile.c
>> ===================================================================
>> --- gcc/auto-profile.c (revision 205354)
>> +++ gcc/auto-profile.c (working copy)
>> @@ -1069,44 +1069,6 @@ afdo_find_equiv_class (void)
>>      }
>>  }
>>
>> -/* If a baisk block only has one in/out edge, then the bb count and he
>> -   edge count should be the same.
>> -   IS_SUCC is true if the out edge of the basic block is examined.
>> -   Return TRUE if any basic block/edge count is changed.  */
>> -
>> -static bool
>> -afdo_propagate_single_edge (bool is_succ)
>> -{
>> -  basic_block bb;
>> -  bool changed = false;
>> -
>> -  FOR_EACH_BB (bb)
>> -    if (is_succ ? single_succ_p (bb) : single_pred_p (bb))
>> -      {
>> - edge e = is_succ ? single_succ_edge (bb) : single_pred_edge (bb);
>> - if (((e->flags & EDGE_ANNOTATED) == 0)
>> -    && ((bb->flags & BB_ANNOTATED) != 0))
>> -  {
>> -    e->count = bb->count;
>> -    e->flags |= EDGE_ANNOTATED;
>> -    changed = true;
>> -  }
>> - else if (((e->flags & EDGE_ANNOTATED) != 0)
>> -    && ((bb->flags & BB_ANNOTATED) == 0))
>> -  {
>> -    bb->count = e->count;
>> -    bb->flags |= BB_ANNOTATED;
>> -    changed = true;
>> -  }
>> - else if (bb->count != e->count)
>> -  {
>> -    e->count = bb->count = MAX (bb->count, e->count);
>> -    changed = true;
>> -  }
>> -      }
>> -  return changed;
>> -}
>> -
>>  /* If a basic block's count is known, and only one of its in/out edges' count
>>     is unknown, its count can be calculated.
>>     Meanwhile, if all of the in/out edges' counts are known, then the basic
>> @@ -1115,7 +1077,7 @@ afdo_find_equiv_class (void)
>>     Return TRUE if any basic block/edge count is changed.  */
>>
>>  static bool
>> -afdo_propagate_multi_edge (bool is_succ)
>> +afdo_propagate_edge (bool is_succ)
>>  {
>>    basic_block bb;
>>    bool changed = false;
>> @@ -1281,14 +1243,10 @@ afdo_propagate (void)
>>      {
>>        changed = false;
>>
>> -      if (afdo_propagate_single_edge (true))
>> +      if (afdo_propagate_edge (true))
>>   changed = true;
>> -      if (afdo_propagate_single_edge (false))
>> +      if (afdo_propagate_edge (false))
>>   changed = true;
>> -      if (afdo_propagate_multi_edge (true))
>> - changed = true;
>> -      if (afdo_propagate_multi_edge (false))
>> - changed = true;
>>        afdo_propagate_circuit ();
>>      }
>>  }