From: Bernd Schmidt <bschmidt@redhat.com>
To: Segher Boessenkool <segher@kernel.crashing.org>, gcc-patches@gcc.gnu.org
Cc: dje.gcc@gmail.com
Subject: Re: [PATCH 8/9] shrink-wrap: shrink-wrapping for separate concerns
Date: Fri, 15 Jul 2016 12:42:00 -0000 [thread overview]
Message-ID: <e73f805d-c6f6-43e6-34b3-1d2f89a92fc3@redhat.com> (raw)
In-Reply-To: <019d5b4c3f6b8119e1511e33a16a8ea96078b094.1465347472.git.segher@kernel.crashing.org>
I still have misgivings about all the changes needed to the following
passes, but I guess there's no choice but to live with it. So, I'm
trying to look at this patch, but I'm finding it fairly impenetrable and
underdocumented.
> + /* The concerns for which we want a prologue placed on this BB. */
> + sbitmap pro_concern;
> +
> + /* The concerns for which we placed code at the start of the BB. */
> + sbitmap head_concern;
What's the difference?
> + /* The frequency of executing the prologue for this BB and all BBs
> + dominated by it. */
> + gcov_type cost;
Is this frequency consideration the only thing that attempts to prevent
placing prologue insns into loops?
> +
> +/* Destroy the pass-specific data. */
> +static void
> +fini_separate_shrink_wrap (void)
> +{
> + basic_block bb;
> + FOR_ALL_BB_FN (bb, cfun)
> + if (bb->aux)
> + {
> + sbitmap_free (SW (bb)->has_concern);
> + sbitmap_free (SW (bb)->pro_concern);
> + sbitmap_free (SW (bb)->head_concern);
> + sbitmap_free (SW (bb)->tail_concern);
> + free (bb->aux);
> + bb->aux = 0;
> + }
> +}
Almost makes me want to ask for an sbitmap variant allocated on obstacks.
> + /* If this block does have the concern itself, or it is cheaper to
> + put the prologue here than in all the descendants that need it,
> + mark it so. If it is the same cost, put it here if there is no
> + block reachable from this block that does not need the prologue.
> + The actual test is a bit more stringent but catches most cases. */
There's some oddness here with the leading whitespace.
> +/* Mark HAS_CONCERN for every block dominated by at least one block with
> + PRO_CONCERN set, starting at HEAD. */
I see a lot of code dealing with the placement of prologue
parts/concerns/components, but very little dealing with how to place
epilogues, leading me to wonder whether we could do better wrt the
latter. Shouldn't there be some mirror symmetry, i.e.
spread_concerns_backwards?
> + {
> + if (first_visit)
> + {
> + bitmap_ior (SW (bb)->has_concern, SW (bb)->pro_concern, concern);
> +
> + if (first_dom_son (CDI_DOMINATORS, bb))
> + {
> + concern = SW (bb)->has_concern;
> + bb = first_dom_son (CDI_DOMINATORS, bb);
> + continue;
> + }
Calling first_dom_son twice with the same args? More importantly, this
first_visit business seems very confusing. I'd try to find a way to
merge this if with the places that set first_visit to true. Also -
instead of having a "continue;" here it seems the code inside the if
represents an inner loop that should be written explicitly. There are
two loops with such a structure.
> +/* If we cannot handle placing some concern's prologues or epilogues where
> + we decided we should place them, unmark that concern in CONCERNS so
> + that it is not wrapped separately. */
> +static void
> +disqualify_problematic_concerns (sbitmap concerns)
> +{
> + sbitmap pro = sbitmap_alloc (SBITMAP_SIZE (concerns));
> + sbitmap epi = sbitmap_alloc (SBITMAP_SIZE (concerns));
> +
> + basic_block bb;
> + FOR_EACH_BB_FN (bb, cfun)
> + {
> + edge e;
> + edge_iterator ei;
> + FOR_EACH_EDGE (e, ei, bb->succs)
> + {
> + bitmap_and_compl (epi, SW (e->src)->has_concern,
> + SW (e->dest)->has_concern);
> + bitmap_and_compl (pro, SW (e->dest)->has_concern,
> + SW (e->src)->has_concern);
What is the purpose of this?
> +/* Place code for prologues and epilogues for CONCERNS where we can put
> + that code at the start of basic blocks. */
> +static void
> +do_common_heads_for_concerns (sbitmap concerns)
The function name should probably have some combination of the strings
emit_ and _at or _into to make it clear what it's doing. This and the
following function have some logical operations on the bitmaps which are
not explained anywhere. In general a much better overview of the
intended operation of this pass is needed.
> + {
> + bitmap_and_compl (epi, SW (e->src)->has_concern,
> + SW (e->dest)->has_concern);
> + bitmap_and_compl (pro, SW (e->dest)->has_concern,
> + SW (e->src)->has_concern);
> + bitmap_and (epi, epi, concerns);
> + bitmap_and (pro, pro, concerns);
> + bitmap_and_compl (epi, epi, SW (e->dest)->head_concern);
> + bitmap_and_compl (pro, pro, SW (e->dest)->head_concern);
> + bitmap_and_compl (epi, epi, SW (e->src)->tail_concern);
> + bitmap_and_compl (pro, pro, SW (e->src)->tail_concern);
Likewise here.
Bernd
next prev parent reply other threads:[~2016-07-15 12:42 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-08 1:48 [PATCH 0/9] separate shrink-wrapping Segher Boessenkool
2016-06-08 1:48 ` [PATCH 2/9] cfgcleanup: Don't confuse CFI when -fshrink-wrap-separate Segher Boessenkool
2016-06-08 1:48 ` [PATCH 1/9] separate shrink-wrap: New command-line flag, status flag, hooks, and doc Segher Boessenkool
2016-06-08 1:48 ` [PATCH 3/9] dce: Don't dead-code delete separately wrapped restores Segher Boessenkool
2016-06-08 1:53 ` [PATCH 6/9] sel-sched: Don't mess with register restores Segher Boessenkool
2016-06-08 1:53 ` [PATCH 4/9] regrename: Don't rename restores Segher Boessenkool
2016-06-08 1:54 ` [PATCH 7/9] cprop: Leave RTX_FRAME_RELATED_P instructions alone Segher Boessenkool
2016-06-08 1:54 ` [PATCH 5/9] regrename: Don't run if function was separately shrink-wrapped Segher Boessenkool
2016-06-08 9:18 ` Bernd Schmidt
2016-09-09 18:41 ` Jeff Law
2016-09-09 20:56 ` Segher Boessenkool
2016-09-09 23:12 ` Jeff Law
2016-09-10 6:59 ` Segher Boessenkool
2016-09-12 16:36 ` Jeff Law
[not found] ` <CAGWvny=fHHZtKF4_D2098+3PTPPzxtg3EjKDWHyJwUxz8g_tEA@mail.gmail.com>
[not found] ` <CAGWvnymZVg_FR_PHqhwkgrAkHDntVMEiG4shfst_GA9OnZKvWg@mail.gmail.com>
[not found] ` <CAGWvnykQ3oz0UpcF6U1WYivbJww65h2EH5n3FocQ8JGY9hrOrA@mail.gmail.com>
2016-09-12 17:04 ` Jeff Law
2016-09-14 13:08 ` Segher Boessenkool
2016-09-14 13:18 ` Bernd Schmidt
2016-09-14 14:01 ` Segher Boessenkool
2016-09-14 14:54 ` Bernd Schmidt
2016-09-14 16:33 ` Segher Boessenkool
2016-09-14 19:10 ` Jeff Law
2016-09-14 17:55 ` Jeff Law
2016-09-14 19:13 ` Segher Boessenkool
2016-09-14 19:36 ` Jeff Law
2016-09-14 18:21 ` Jeff Law
2016-09-14 19:13 ` Segher Boessenkool
2016-09-14 19:38 ` Jeff Law
2016-09-14 22:34 ` Segher Boessenkool
2016-09-15 17:28 ` Jeff Law
2016-09-19 17:11 ` Segher Boessenkool
2016-09-14 20:04 ` Jeff Law
2016-09-14 22:51 ` Segher Boessenkool
2016-06-08 2:03 ` [PATCH 8/9] shrink-wrap: shrink-wrapping for separate concerns Segher Boessenkool
2016-07-15 12:42 ` Bernd Schmidt [this message]
2016-07-18 16:34 ` Segher Boessenkool
2016-07-18 17:03 ` Bernd Schmidt
2016-07-19 14:46 ` Segher Boessenkool
2016-07-19 14:49 ` Bernd Schmidt
2016-07-19 15:35 ` Segher Boessenkool
2016-07-20 11:23 ` Bernd Schmidt
2016-07-20 15:06 ` Segher Boessenkool
2016-06-08 2:04 ` [PATCH 9/9] rs6000: Separate shrink-wrapping Segher Boessenkool
2016-06-08 11:56 ` [PATCH 0/9] separate shrink-wrapping Bernd Schmidt
2016-06-08 12:45 ` Eric Botcazou
2016-06-08 15:16 ` Segher Boessenkool
2016-06-08 16:43 ` Bernd Schmidt
2016-06-08 17:26 ` Segher Boessenkool
2016-06-29 23:06 ` Bernd Schmidt
2016-06-29 23:24 ` Segher Boessenkool
2016-07-04 8:57 ` Segher Boessenkool
2016-06-14 21:24 ` Segher Boessenkool
2016-07-08 10:42 ` Bernd Schmidt
2016-07-08 12:11 ` Segher Boessenkool
2016-07-08 13:16 ` David Malcolm
2016-07-08 13:45 ` Segher Boessenkool
2016-07-08 14:35 ` Bill Schmidt
2016-06-09 16:12 ` Jeff Law
2016-06-09 19:57 ` Segher Boessenkool
2016-06-28 0:22 ` PING " Segher Boessenkool
2016-07-07 10:16 ` PING x2 " Segher Boessenkool
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=e73f805d-c6f6-43e6-34b3-1d2f89a92fc3@redhat.com \
--to=bschmidt@redhat.com \
--cc=dje.gcc@gmail.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=segher@kernel.crashing.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).