> Great! Is this the LTO merging you were talking about in an earlier
> message, or the gcov runtime fix (that would presumably not be
> lto-specific)?
It is the LTO path - we need to merge profiles there anyway for his code
unification
work.
> > I have patch to track this. Moreover vforks seems to produce repeated
> > merging of results.
>
> Aha, does this explain the gimp issue as well?
Not really - we still need to debug why we hit cold section so many times with
partitioning. I sitll think easier approach will be to lock the cold section
and
then start probably with testsuite (i.e. write script to compile the small
testcases
with FDO + partitioning and see what crash by hitting cold section).
> >
> > Is it really necessary to run this from internal loop of the cfgcleanup?
>
> The reason I added it here is that just below there is a call to
> verify_flow_info, and that will fail with the new verification.
Hmm, OK, I suppose we run the cleanup after partitioning just once or twice,
right?
We can track this incrementally - I am not sure if we put it from the internal
iteration
loop we would get anything substantial either.
Removing unreachable blocks twice is however ugly.
> +/* Ensure that all hot bbs are included in a hot path through the
> + procedure. This is done by calling this function twice, once
> + with WALK_UP true (to look for paths from the entry to hot bbs) and
> + once with WALK_UP false (to look for paths from hot bbs to the exit).
> + Returns the updated value of COLD_BB_COUNT and adds newly-hot bbs
> + to BBS_IN_HOT_PARTITION. */
> +
> +static unsigned int
> +sanitize_hot_paths (bool walk_up, unsigned int cold_bb_count,
> + vec<basic_block> *bbs_in_hot_partition)
> +{
> + /* Callers check this. */
> + gcc_checking_assert (cold_bb_count);
> +
> + /* Keep examining hot bbs while we still have some left to check
> + and there are remaining cold bbs. */
> + vec<basic_block> hot_bbs_to_check = bbs_in_hot_partition->copy ();
> + while (! hot_bbs_to_check.is_empty ()
> + && cold_bb_count)
> + {
> + basic_block bb = hot_bbs_to_check.pop ();
> + vec<edge, va_gc> *edges = walk_up ? bb->preds : bb->succs;
> + edge e;
> + edge_iterator ei;
> + int highest_probability = 0;
> + int highest_freq = 0;
> + gcov_type highest_count = 0;
> + bool found = false;
> +
> + /* Walk the preds/succs and check if there is at least one already
> + marked hot. Keep track of the most frequent pred/succ so that we
> + can mark it hot if we don't find one. */
> + FOR_EACH_EDGE (e, ei, edges)
> + {
> + basic_block reach_bb = walk_up ? e->src : e->dest;
> +
> + if (e->flags & EDGE_DFS_BACK)
> + continue;
> +
> + if (BB_PARTITION (reach_bb) != BB_COLD_PARTITION)
> + {
> + found = true;
> + break;
> + }
> + /* The following loop will look for the hottest edge via
> + the edge count, if it is non-zero, then fallback to the edge
> + frequency and finally the edge probability. */
> + if (e->count > highest_count)
> + highest_count = e->count;
> + int edge_freq = EDGE_FREQUENCY (e);
> + if (edge_freq > highest_freq)
> + highest_freq = edge_freq;
> + if (e->probability > highest_probability)
> + highest_probability = e->probability;
> + }
> +
> + /* If bb is reached by (or reaches, in the case of !WALK_UP) another
> hot
> + block (or unpartitioned, e.g. the entry block) then it is ok. If
> not,
> + then the most frequent pred (or succ) needs to be adjusted. In the
> + case where multiple preds/succs have the same frequency (e.g. a
> + 50-50 branch), then both will be adjusted. */
> + if (found)
> + continue;
> +
> + FOR_EACH_EDGE (e, ei, edges)
> + {
> + if (e->flags & EDGE_DFS_BACK)
> + continue;
> + /* Select the hottest edge using the edge count, if it is non-zero,
> + then fallback to the edge frequency and finally the edge
> + probability. */
> + if (highest_count)
> + {
> + if (e->count < highest_count)
> + continue;
> + }
> + else if (highest_freq)
The frequency condition needs to be done only when you walk predecestors - when
you walk down the edge probabilities are just fine.
The patch seems OK to me now. I will make our FDO tester to use partitioning
so we get
this benchmarked a bit.
Honza
