On Fri, Aug 2, 2013 at 4:04 PM, Steven Bosscher <stevenb....@gmail.com> wrote:
> On Fri, Aug 2, 2013 at 5:05 PM, Jan Hubicka <hubi...@ucw.cz> wrote:
>>> +/* Called when block BB has been reassigned to a different partition,
>>> + to ensure that the region crossing attributes are updated. */
>>> +
>>> +static void
>>> +fixup_bb_partition (basic_block bb)
>>> +{
>>> + edge e;
>>> + edge_iterator ei;
>>> +
>>> + /* Now need to make bb's pred edges non-region crossing. */
>>> + FOR_EACH_EDGE (e, ei, bb->preds)
>>> + {
>>> + fixup_partition_crossing (e);
>>> + }
>>> +
>>> + /* Possibly need to make bb's successor edges region crossing,
>>> + or remove stale region crossing. */
>>> + FOR_EACH_EDGE (e, ei, bb->succs)
>>> + {
>>> + if ((e->flags & EDGE_FALLTHRU)
>>> + && BB_PARTITION (bb) != BB_PARTITION (e->dest)
>>> + && e->dest != EXIT_BLOCK_PTR)
>>> + force_nonfallthru (e);
>>> + else
>>> + fixup_partition_crossing (e);
>>> + }
>>> +}
>>
>> Is there particular reason why preds can not be fallhtrus
>
> Yes, by definition a crossing edge cannot fall through. There is
> always a control transfer from one section to another.
>
>
>>> +/* Sanity check partition hotness to ensure that basic blocks in
>>> + the cold partition don't dominate basic blocks in the hot partition.
>>> + If FLAG_ONLY is true, report violations as errors. Otherwise
>>> + re-mark the dominated blocks as cold, since this is run after
>>> + cfg optimizations that may make hot blocks previously reached
>>> + by both hot and cold blocks now only reachable along cold paths. */
>>
>> With profile, I suppose we can have cold blocks dominating hot blocks when
>> the
>> hot blocks is in loop whose trip count is high enough.
>
> That is the common case, actually.
>
>> Indeed for partitioning
>> reasons it does not make sense to push those into different section.
>
> The partitioning algrorithm makes sure this doesn't happen. The
> hottest path from the entry block to a hot basic block is always part
> of the hot partition.
Well, at least with this patch that will be true. The trunk version
just partitions based on the bb's count without regard to paths.
Thanks,
Teresa
>
>
>> I also wonder, if we finally get the pass stable, can we enable it by default
>> and offline probably cold blocks w/o profile?
>
> That is the general idea behind all this work, obviously ;-)
>
>> Primarily blocks reachable only
>> by EH + blocks leading to a crash or throw(). For C++ those should be common
>> enough to make a difference...
>
> Yup, and IIRC Theresa posted some numbers that showed this.
>
> Ciao!
> Steven
--
Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413
