On 28/10/2011, at 7:24 PM, Maxim Kuvyrkov wrote:
> On 20/10/2011, at 10:32 PM, Jan Hubicka wrote:
>
>> Hi,
>>> Jan,
>>>
>>> The following patch started as a one-liner for ipa-inline-analysis.c:
>>> account_size_time() to merge predicates when we are adding data to entry[0]
>>> (i.e., when space for 32 size_time entries is exhausted):
>>>
>>> @@ -537,6 +592,9 @@ account_size_time (struct inline_summary
>>> }
>>> else
>>> {
>>> + e->predicate = or_predicates (summary->conds, &e->predicate, pred);
>>> e->size += size;
>>> e->time += time;
>>> if (e->time > MAX_TIME * INLINE_TIME_SCALE)
>>
>> As we discussed, this is not needed in current form because we arrange first
>> predicate to be always
>> true and thus we could always place there all the costs that did not fit
>> elwhere.
>>
>> The patch has a problem with fact that the predicates must be always
>> conservative i.e. when
>> they are proved to be false the code must be unreachable after inlining.
>
> I don't understand your point. The OR-ing of the predicates allows us to
> merge size_time_entries and keep the total number of them under a desired
> limit. Currently all merging goes into entry[0], and the patch makes the
> extra information to get distributed across more entries. Because we OR the
> predicates, we keep the information conservative; now in order to say that
> certain code will be unreachable the inliner has to prove to be false the
> OR-ed predicate.
>
> Now, one can argue whether it is actually a benefit to distribute the
> information more evenly and, consequently, making more predicates harder to
> disprove. In current scheme we have the surplus of size_time information
> under one impossible-to-disprove predicate and many entries with
> easier-to-disprove-predicates. My patch changes the situation to having most
> of the size_time information in entries with harder-but-possible-to-disprove
> predicates.
>
> Am I missing something?
Ping.
Though this patch is not motivated by a real testcase, I want to confirm (or
correct) my understanding of the IPA context-tracking infrastructure.
Jan, does the above sound reasonable as to why predicates would still be
conservative after the patch?
Thank you,
--
Maxim Kuvyrkov
CodeSourcery / Mentor Graphics
