From: "Paulo J. Matos" <paulo@matos-sorge.com>
To: gcc@gcc.gnu.org
Subject: Re: Move insn out of the way
Date: Wed, 10 Aug 2011 13:46:00 -0000 [thread overview]
Message-ID: <j1u23d$6og$1@dough.gmane.org> (raw)
In-Reply-To: <CAFiYyc0y9Z8N2YHyw8AoMTtiZUfsaU5u4CDiD+6u0CiMOGfdmA@mail.gmail.com>
On 10/08/11 12:40, Richard Guenther wrote:
>
> On x86 we expand the code to ((xl& al) ^ al) | ((xh& ah) ^ ah) == 0
> which is then if-converted. Modified testcase:
>
> long long x;
> _Bool __attribute__((regparm(2))) mask (long long a)
> {
> return (x& a) == a;
> }
>
> on i?86 gets you
>
> mask:
> .LFB0:
> .cfi_startproc
> pushl %ebx
> .cfi_def_cfa_offset 8
> .cfi_offset 3, -8
> movl %eax, %ebx
> andl x, %ebx
> movl %edx, %ecx
> andl x+4, %ecx
> xorl %ebx, %eax
> xorl %ecx, %edx
> orl %edx, %eax
> sete %al
> popl %ebx
> .cfi_restore 3
> .cfi_def_cfa_offset 4
> ret
>
> so I wonder if you should investigate why the xor variant doesn't trigger
> for you?
I can reproduce this result in GCC 4.6.1 for x86.
I can't understand what you mean by this though. From inspecting the
logs it seems that the if-conversion is done manually at expand time.
The final pass before expand shows the original (x & a) == a, however,
after expand the rtl already contains xor, ior, etc. So I guess I would
need to do something similar in my backend. I can't however, find in the
i386(.md|.c) where this is actually happening.
> On i?86 if-conversion probably solves your specific issue,
> but I guess the initial expansion is where you could improve placement
> of the 1 (after all, the 0 is after the jumps).
>
This is happening on my own backend so I guess anything that is
implemented to do if-conversion on i386 needs to be implemented also on
my backend. Can you point me to the code on i386 so I can take a look at it?
Cheers,
--
PMatos
next prev parent reply other threads:[~2011-08-10 13:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-10 11:20 Paulo J. Matos
2011-08-10 11:40 ` Richard Guenther
2011-08-10 11:42 ` Richard Guenther
2011-08-10 13:55 ` Paulo J. Matos
[not found] ` <4E431BD8.8060705@redhat.com>
2011-08-11 8:12 ` Paulo J. Matos
2011-08-11 8:49 ` Richard Guenther
2011-08-11 14:27 ` Vladimir Makarov
2011-08-12 10:01 ` Paulo J. Matos
2011-08-12 14:22 ` Vladimir Makarov
2011-08-12 15:06 ` Paulo J. Matos
2011-08-12 16:12 ` Jeff Law
2011-08-11 12:22 ` Paulo J. Matos
2011-08-10 13:46 ` Paulo J. Matos [this message]
2011-08-10 13:51 ` Richard Guenther
2011-08-10 14:14 ` Paulo J. Matos
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='j1u23d$6og$1@dough.gmane.org' \
--to=paulo@matos-sorge.com \
--cc=gcc@gcc.gnu.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).