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Re: [PATCH] decide edge's hotness when there is profile info


Not for instrumented FDO (not as I know of). But for AutoFDO, this
could be a potential risk because some callee is marked unlikely
executed simply because they are inlined and eliminated in the O2
binary. But in ipa-inline it will not get inlined because the edge is
not hot from cgraph_maybe_hot_edge_p (because callee is
UNLIKELY_EXECUTED), while the edge->count is actually hot.

Dehao

On Mon, Oct 14, 2013 at 9:13 AM, Xinliang David Li <davidxl@google.com> wrote:
> Looks like there is some inconsistency between edge hotness and callee
> frequency?
>
> David
>
> On Mon, Oct 14, 2013 at 9:08 AM, Dehao Chen <dehao@google.com> wrote:
>> This patch forces to use profile info to check if an edge is hot when
>> profile is available.
>>
>> Bootstrapped and passed regression tests.
>>
>> OK for trunk?
>>
>> Thanks,
>> Dehao
>>
>> gcc/ChangeLog:
>> 2013-10-14  Dehao Chen  <dehao@google.com>
>> * predict.c(cgraph_maybe_hot_edge_p): Decide edge's hotness from profile.
>>
>> Index: gcc/predict.c
>> ===================================================================
>> --- gcc/predict.c (revision 203568)
>> +++ gcc/predict.c (working copy)
>> @@ -185,10 +185,8 @@ maybe_hot_bb_p (struct function *fun, const_basic_
>>  bool
>>  cgraph_maybe_hot_edge_p (struct cgraph_edge *edge)
>>  {
>> -  if (profile_info && flag_branch_probabilities
>> -      && !maybe_hot_count_p (NULL,
>> -                             edge->count))
>> -    return false;
>> +  if (profile_info && flag_branch_probabilities)
>> +    return maybe_hot_count_p (NULL, edge->count);
>>    if (edge->caller->frequency == NODE_FREQUENCY_UNLIKELY_EXECUTED
>>        || (edge->callee
>>    && edge->callee->frequency == NODE_FREQUENCY_UNLIKELY_EXECUTED))


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