From: Jeff Law <law@redhat.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Don't allow FSM threader to create irreducible loops unless it eliminates a multi-way branch
Date: Wed, 21 Oct 2015 14:53:00 -0000 [thread overview]
Message-ID: <5627A4B5.6090409@redhat.com> (raw)
In-Reply-To: <CAFiYyc3zH1SCKZZ1T=uoooZdPXO+xd0sD5boq5o0uo33XSjKCg@mail.gmail.com>
On 10/21/2015 02:56 AM, Richard Biener wrote:
> On Mon, Oct 19, 2015 at 6:23 PM, Jeff Law <law@redhat.com> wrote:
>> If I hack up GCC's old jump threader to avoid threading across backedges and
>> instead let the FSM threader handle that case, then we end up with cases
>> where the FSM threader creates irreducible loops with marginal benefit.
>>
>> This can be seen in ssa-dom-thread-2{d,e,f}.c.
>>
>> We've long avoided such threads in the old jump threader. We generally want
>> to avoid them in the FSM threader as well. The only case where we're going
>> to allow them is when we're able to eliminate a multi-way branch from the
>> loop.
>>
>> Bootstrapped and regression tested on x86_64-linux-gnu. Also tested the
>> above mentioned testcases with my hacked up compiler.
>>
>> Installed on the trunk.
>
> Note that this fixed some of the size regressions I see on SPEC CPU 2000
> but not all, esp. 176.gcc seems to be as bad as before (seen with plain -O2
> on x86_64).
I haven't started looking at them explicitly yet. Good to know it
helped some though.
jeff
prev parent reply other threads:[~2015-10-21 14:44 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-19 16:24 Jeff Law
2015-10-21 0:05 ` Hans-Peter Nilsson
2015-10-21 0:13 ` Bernd Schmidt
2015-10-21 4:46 ` Jeff Law
2015-10-21 12:12 ` Hans-Peter Nilsson
2015-10-21 14:44 ` Jeff Law
2015-10-21 9:06 ` Richard Biener
2015-10-21 14:53 ` Jeff Law [this message]
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=5627A4B5.6090409@redhat.com \
--to=law@redhat.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=richard.guenther@gmail.com \
/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).