From: Richard Henderson <rth@redhat.com>
To: Jason Merrill <jason@redhat.com>
Cc: Diego Novillo <dnovillo@redhat.com>,
gcc@gcc.gnu.org, mark@codesourcery.com
Subject: Re: PR c++/5504: Optimization breaks wei-ku-1 from blitz
Date: Tue, 09 Apr 2002 00:20:00 -0000 [thread overview]
Message-ID: <20020409000042.A7972@redhat.com> (raw)
In-Reply-To: <wvlhempwz9b.fsf@prospero.cambridge.redhat.com>; from jason@redhat.com on Fri, Apr 05, 2002 at 11:34:40PM +0100
On Fri, Apr 05, 2002 at 11:34:40PM +0100, Jason Merrill wrote:
> Unfortunately, the backend doesn't seem to be prepared to handle this
> number of EH regions; many of the data structures can only be searched
> linearly. For the four-term case, gprof shows that we're spending the vast
> majority of our time traversing them:
>
> % cumulative self self total
> time seconds seconds calls ms/call ms/call name
> 37.35 211.09 211.09 110832 1.90 2.32 maybe_remove_eh_handler
> 26.59 361.36 150.27 344409 0.44 0.44 in_expr_list_p
> 10.00 417.89 56.53 305399 0.19 0.19 next_nonnote_insn
> 6.59 455.11 37.22 28896 1.29 1.29 remove_exception_handler_label
[...]
> I'm not sure what to do about this. We need to support this sort of code;
> this is a very common C++ programming idiom. Obvious ways to improve
> performance would be:
>
> [1] Adjust the EH data structures so that we can do more efficient
> searches in them.
> [2] Try to avoid creating EH regions that will just be deleted again.
> If nothing in the region can throw, we can discard it at
> expand_eh_region_end time.
It turns out that [2] is annoyingly difficult. FIXUP regions created
by expand_cleanups want to insert code into the *parent* of a CLEANUP
region, after that region has already been finalized by
expand_eh_region_end. I.e. if we simply fail to create the cleanup
region based on the fact that it'll never be used, we'll not have all
the data structures needed to resolve the fixup region. :-(
Doing [1] is within our power. I found a whole series of quadratic
(or worse) operations here -- not all of them in the EH code.
I'm currently testing a patch that brings the original test case to
% cumulative self self total
time seconds seconds calls s/call s/call name
5.14 7.34 7.34 2662100 0.00 0.00 walk_tree
4.57 13.87 6.53 701 0.01 0.01 fixup_var_refs_insns
4.30 20.01 6.14 34516896 0.00 0.00 ggc_alloc
3.20 24.58 4.57 62692969 0.00 0.00 statement_code_p
2.96 28.81 4.23 7488030 0.00 0.00 fixup_var_refs_1
2.70 32.66 3.85 77455616 0.00 0.00 add_insn
expand : 207.49 (59%) usr 8.39 (68%) sys 216.25 (59%) wall
parser : 38.15 (11%) usr 0.77 ( 6%) sys 38.52 (11%) wall
garbage collection : 29.99 ( 9%) usr 1.31 (11%) sys 31.30 ( 9%) wall
cfg construction : 18.96 ( 5%) usr 0.46 ( 4%) sys 19.56 ( 5%) wall
cfg cleanup : 16.27 ( 5%) usr 0.04 ( 0%) sys 16.23 ( 4%) wall
TOTAL : 351.17 12.35 363.83
I.e. we're down below 6 minutes compile time instead of 7 hours.
Unfortunately, it still consumes unacceptable amounts of memory.
Somewhere near 1.2GB peak. I think I can improve this by eliding
some of the *code* associated with cleanup regions, even though
I cannot elide the cleanup region data structure itself.
I'll test the patch I have overnight and post if it succeeds.
r~
prev parent reply other threads:[~2002-04-09 7:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-25 21:41 Diego Novillo
2002-04-03 18:04 ` Jason Merrill
2002-04-03 19:23 ` Diego Novillo
2002-04-05 15:08 ` Jason Merrill
2002-04-05 16:14 ` Jason Merrill
2002-04-06 15:36 ` PR " Mark Mitchell
2002-04-06 23:38 ` Richard Henderson
2002-04-09 0:20 ` Richard Henderson [this message]
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