On Wed, 23 Sep 2020, Tom de Vries wrote:
> On 9/23/20 9:28 AM, Richard Biener wrote:
> > On Tue, 22 Sep 2020, Tom de Vries wrote:
> >
> >> [ was: Re: [Patch] [middle-end & nvptx] gcc/tracer.c: Don't split BB
> >> with SIMT LANE [PR95654] ]
> >>
> >> On 9/16/20 8:20 PM, Alexander Monakov wrote:
> >>>
> >>>
> >>> On Wed, 16 Sep 2020, Tom de Vries wrote:
> >>>
> >>>> [ cc-ing author omp support for nvptx. ]
> >>>
> >>> The issue looks familiar. I recognized it back in 2017 (and LLVM people
> >>> recognized it too for their GPU targets). In an attempt to get agreement
> >>> to fix the issue "properly" for GCC I found a similar issue that affects
> >>> all targets, not just offloading, and filed it as PR 80053.
> >>>
> >>> (yes, there are no addressable labels involved in offloading, but
> >>> nevertheless
> >>> the nature of the middle-end issue is related)
> >>
> >> Hi Alexander,
> >>
> >> thanks for looking into this.
> >>
> >> Seeing that the attempt to fix things properly is stalled, for now I'm
> >> proposing a point-fix, similar to the original patch proposed by Tobias.
> >>
> >> Richi, Jakub, OK for trunk?
> >
> > I notice that we call ignore_bb_p many times in tracer.c but one call
> > is conveniently early in tail_duplicate (void):
> >
> > int n = count_insns (bb);
> > if (!ignore_bb_p (bb))
> > blocks[bb->index] = heap.insert (-bb->count.to_frequency (cfun),
> > bb);
> >
> > where count_insns already walks all stmts in the block. It would be
> > nice to avoid repeatedly walking all stmts, maybe adjusting the above
> > call is enough and/or count_insns can compute this and/or the ignore_bb_p
> > result can be cached (optimize_bb_for_size_p might change though,
> > but maybe all other ignore_bb_p calls effectively just are that,
> > checks for blocks that became optimize_bb_for_size_p).
> >
>
> This untested follow-up patch tries something in that direction.
>
> Is this what you meant?
Yeah, sort of.
+static bool
+cached_can_duplicate_bb_p (const_basic_block bb)
+{
+ if (can_duplicate_bb)
is there any path where can_duplicate_bb would be NULL?
+ {
+ unsigned int size = SBITMAP_SIZE (can_duplicate_bb);
+ /* Assume added bb's should be ignored. */
+ if ((unsigned int)bb->index < size
+ && bitmap_bit_p (can_duplicate_bb_computed, bb->index))
+ return !bitmap_bit_p (can_duplicate_bb, bb->index);
yes, newly added bbs should be ignored so,
}
- return false;
+ bool val = compute_can_duplicate_bb_p (bb);
+ if (can_duplicate_bb)
+ cache_can_duplicate_bb_p (bb, val);
no need to compute & cache for them, just return true (because
we did duplicate them)?
Thanks,
Richard.
> Thanks,
> - Tom
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imend
