[Re: optimization/8412: Code generation problem with -march=k6

[Re: optimization/8412: Code generation problem with -march=k6

[Jim Bray]

The following reply was made to PR optimization/8412; it has been noted by GNATS.

From: Jim Bray <jb@as220.org>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: [Re: optimization/8412: Code generation problem with -march=k6
Date: 28 Jan 2003 09:48:33 -0500

   I think I'm seeing this same bug, with 
 gcc version 3.2.1 20021207 (Gentoo Linux 3.2.1-20021207)
  I've noticed considerable instability with multimedia things including
 xine, and have been studying an easily reproducible problem with
 xmms. I'd assumed it was 3dnow related, but testing has zeroed me in
 on a combination of -funroll-all-loops and -O[23].
 
   Here are my crude notes to date. Not yet a good bug-report,
 
 The test is compiling and running xmms and doing a particular
 operation with it. My system is a k6-2.
 
 -finline-functions is used in all tests.
 
 CFLAGS='-march=k6-2 -g -O1' works.
 CFLAGS='-march=k6-2 -g -O1 -ffast-math' works.
 CFLAGS='-march=k6-2 -g -O1 -ffast-math -funroll-all-loops' works.
 CFLAGS='-march=k6-2 -g -O2 -ffast-math -funroll-all-loops' FAILS.
 CFLAGS='-march=k6-2 -g -O2 -ffast-math' works.
 CFLAGS='-march=k6-2 -O2 -ffast-math' works.
 
   The xmms configuration normally uses -funroll-all-loops, and
 I was seeing consistent failure with any variant of -m{cpu,arch}=
 {k6,k6-2} -O[23], which is not reflected above. The problem went
 away when the k6-specific flags were removed. I did not start
 getting any k6-specific build successes until I started dropping
 below -O2 and -funroll-all-loops.
 
   I did some studying of this with gdb, which seemed to be zeroing me
 into an area of code which became an unrolled loop.
 
  Bug I 'sent email to interested parties' from:
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8412
 
 
 -- 
 Jim Bray <jb@as220.org>
 -- 
 Jim Bray <jb@as220.org>