Re: Ping^3 [PATCH V2] Add attribute hot judgement for INLINE_HINT_known_hot hint.

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/30/22 19:44, Cui, Lili wrote:
>> On 10/20/22 19:52, Cui, Lili via Gcc-patches wrote:
>>> Hi Honza,
>>>
>>> Gentle ping
>>> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601934.html
>>>
>>> gcc/ChangeLog
>>>
>>>     * ipa-inline-analysis.cc (do_estimate_edge_time): Add function attribute
>>>     judgement for INLINE_HINT_known_hot hint.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>>     * gcc.dg/ipa/inlinehint-6.c: New test.
>>> ---
>>>    gcc/ipa-inline-analysis.cc              | 13 ++++---
>>>    gcc/testsuite/gcc.dg/ipa/inlinehint-6.c | 47
>> +++++++++++++++++++++++++
>>>    2 files changed, 56 insertions(+), 4 deletions(-)
>>>    create mode 100644 gcc/testsuite/gcc.dg/ipa/inlinehint-6.c
>>>
>>> diff --git a/gcc/ipa-inline-analysis.cc b/gcc/ipa-inline-analysis.cc
>>> index 1ca685d1b0e..7bd29c36590 100644
>>> --- a/gcc/ipa-inline-analysis.cc
>>> +++ b/gcc/ipa-inline-analysis.cc
>>> @@ -48,6 +48,7 @@ along with GCC; see the file COPYING3.  If not see
>>>    #include "ipa-utils.h"
>>>    #include "cfgexpand.h"
>>>    #include "gimplify.h"
>>> +#include "attribs.h"
>>>
>>>    /* Cached node/edge growths.  */
>>>    fast_call_summary<edge_growth_cache_entry *, va_heap>
>>> *edge_growth_cache = NULL; @@ -249,15 +250,19 @@
>> do_estimate_edge_time (struct cgraph_edge *edge, sreal
>> *ret_nonspec_time)
>>>          hints = estimates.hints;
>>>        }
>>>
>>> -  /* When we have profile feedback, we can quite safely identify hot
>>> -     edges and for those we disable size limits.  Don't do that when
>>> -     probability that caller will call the callee is low however, since it
>>> +  /* When we have profile feedback or function attribute, we can quite
>> safely
>>> +     identify hot edges and for those we disable size limits.  Don't do that
>>> +     when probability that caller will call the callee is low
>>> + however, since it
>>>         may hurt optimization of the caller's hot path.  */
>>> -  if (edge->count.ipa ().initialized_p () && edge->maybe_hot_p ()
>>> +  if ((edge->count.ipa ().initialized_p () && edge->maybe_hot_p ()
>>>          && (edge->count.ipa () * 2
>>>    	  > (edge->caller->inlined_to
>>>    	     ? edge->caller->inlined_to->count.ipa ()
>>>    	     : edge->caller->count.ipa ())))
>>> +      || (lookup_attribute ("hot", DECL_ATTRIBUTES (edge->caller->decl))
>>> +	  != NULL
>>> +	 && lookup_attribute ("hot", DECL_ATTRIBUTES (edge->callee->decl))
>>> +	  != NULL))
>>>        hints |= INLINE_HINT_known_hot;
>> Is the theory here that if the user has marked the caller and callee as hot,
>> then we're going to assume an edge between them is hot too?  That's not
>> necessarily true, it could be they're both hot, but via other call chains.  But it's
>> probably a reasonable heuristic in practice.
>>
> Yes,  thanks Jeff.

Thanks for the confirmation.  This is OK for the trunk.

jeff