https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85964
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |hubicka at gcc dot gnu.org
Known to work| |7.3.0
Summary|compile time hog w/ -O3 |[8/9 Regression] compile
|-ftracer |time hog w/ -O3 -ftracer
|-fno-guess-branch-probabili |-fno-guess-branch-probabili
|ty |ty
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Martin Liška from comment #8)
> (In reply to Eric Botcazou from comment #7)
> > Not a regression since #pragma GCC unroll is new.
>
> Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85964#c2 provides
> test-case that does not use GCC unroll.
>
> I see following starting revision with following timeouts:
>
> 5s: r250338
> 10s: r250338
> 20s: r254379
>
> That said I would classify that as regression.
Agreed.
Note for this testcase the behavior looks similar. I cut the # of calls in
half
and get for 8.1:
tree CFG cleanup : 15.12 ( 61%) 0.00 ( 0%) 15.07 ( 60%)
2101 kB ( 4%)
backwards jump threading : 8.36 ( 34%) 0.00 ( 0%) 8.36 ( 33%)
0 kB ( 0%)
while 7.3 has no time spent in those.
I guess the real issue is the tracer pass mis-behaving with
-fno-guess-branch-probabilities since it looks like it will just compute
"random" best traces
if there's no probabilities/counts initialized.
There's obvious disconnect in find_best_{predecessor,successor} and I'm missing
code that makes them return NULL in case that "best" pred/succ doesn't have
profile initialized on the corresponding edge or src/dest BB.
Honza? The following avoids doing anything in tracer to the testcase.
Btw, -ftracer doesn't seem to be needed to
reproduce the backward threading part of this issue, just the CFG cleanup
part (it's tracers CFG cleanup that needs this much time).
diff --git a/gcc/tracer.c b/gcc/tracer.c
index 58f4ec1d72c..e514084b24b 100644
--- a/gcc/tracer.c
+++ b/gcc/tracer.c
@@ -154,10 +154,9 @@ find_best_successor (basic_block bb)
FOR_EACH_EDGE (e, ei, bb->succs)
if (!best || better_p (e, best))
best = e;
- if (!best || ignore_bb_p (best->dest))
+ if (!best || !best->probability.initialized_p () || ignore_bb_p
(best->dest))
return NULL;
- if (best->probability.initialized_p ()
- && best->probability.to_reg_br_prob_base () <= probability_cutoff)
+ if (best->probability.to_reg_br_prob_base () <= probability_cutoff)
return NULL;
return best;
}
@@ -174,10 +173,11 @@ find_best_predecessor (basic_block bb)
FOR_EACH_EDGE (e, ei, bb->preds)
if (!best || better_p (e, best))
best = e;
- if (!best || ignore_bb_p (best->src))
+ if (!best || !best->count ().initialized_p () || ignore_bb_p (best->src))
return NULL;
- if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
- < bb->count.to_frequency (cfun) * branch_ratio_cutoff)
+ if (bb->count.initialized_p ()
+ && (best->count ().to_frequency (cfun) * REG_BR_PROB_BASE
+ < bb->count.to_frequency (cfun) * branch_ratio_cutoff))
return NULL;
return best;
}
