From: Roman Zippel <zippel@linux-m68k.org>
To: gcc <gcc@gcc.gnu.org>
Subject: alias problem during loop pass
Date: Sat, 08 Mar 2003 20:27:00 -0000 [thread overview]
Message-ID: <3E6A4918.C365F399@linux-m68k.org> (raw)
Hi,
I'm currently trying to debug a problem, which causes a few problems for
Debian/m68k. The problem is present at least since 3.2 and also in
latest tree, but it seems not to be in 3.0.
I've put a test case at http://www.xs4all.nl/~zippel/sha.i, it's a
precompiled example from coreutils. Here is the important part:
void
sha_process_block (const void *buffer, size_t len, struct sha_ctx *ctx)
{
const md5_uint32 *words = buffer;
size_t nwords = len / sizeof (md5_uint32);
const md5_uint32 *endp = words + nwords;
md5_uint32 x[16];
[..]
while (words < endp)
{
md5_uint32 tm;
int t;
for (t = 0; t < 16; t++)
{
x[t] = (*words);
words++;
}
First it looks at the small loop and replaces x[t] with a pointer:
-(insn 86 84 87 (set (mem/s:SI (plus:SI (plus:SI (mult:SI (reg/v:SI 47)
- (const_int 4 [0x4]))
- (reg/f:SI 14 %a6))
- (const_int -64 [0xffffffc0])) [5 x S4 A16])
- (mem:SI (reg/v/f:SI 32) [5 S4 A16])) 29 {*m68k.md:976} (nil)
+(insn 86 84 2470 (set (mem/s:SI (reg/f:SI 1137) [5 x S4 A16])
+ (mem:SI (reg/v/f:SI 32) [5 S4 A16])) -1 (nil)
+ (nil))
+
+(insn 2470 86 87 (set (reg/f:SI 1137)
+ (plus:SI (reg/f:SI 1137)
+ (const_int 4 [0x4]))) -1 (nil)
(nil))
The problem is now when it looks at the large loop, the x array is only
read after this and the optimizer thinks now it can move the array out
of the loop. AFAICS it goes wrong in loop.c:load_mems(), it does an
alias analysis with the already modified instructions, but then it uses
loop_info->store_mems to test for dependency tests, but this list still
contains the old reference.
At this point I really could need some help, how this should be fixed
correctly. Any ideas?
bye, Roman
reply other threads:[~2003-03-08 19:48 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
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=3E6A4918.C365F399@linux-m68k.org \
--to=zippel@linux-m68k.org \
--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).