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From: "su at cs dot ucdavis.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/58277] New: wrong code at -O3 (affecting 4.7, 4.8, and trunk)
Date: Thu, 29 Aug 2013 23:30:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58277

            Bug ID: 58277
           Summary: wrong code at -O3 (affecting 4.7, 4.8, and trunk)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk (as well as gcc 4.7 and 4.8) produces wrong code for the
attached testcase on x86_64-linux when compiled at -O3 in 32-bit mode. It is a
regression from 4.6.x.  

This one has been quite nasty to reduce; the attached testcase is the simplest
I was able to get. I believe it doesn't have any undefined behavior. 


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto
--with-gmp=/usr/local/gcc-trunk --with-mpfr=/usr/local/gcc-trunk
--with-mpc=/usr/local/gcc-trunk --with-cloog=/usr/local/gcc-trunk
--prefix=/usr/local/gcc-trunk
Thread model: posix
gcc version 4.9.0 20130829 (experimental) [trunk revision 202067] (GCC) 
$ gcc-trunk -m32 -O2 small.c
$ a.out
0
$ gcc-4.6 -m32 -O3 small.c
$ a.out
0
$ gcc-trunk -m32 -O3 small.c
$ a.out
0
Aborted (core dumped)
$ gcc-4.7 -m32 -O3 small.c
$ a.out
0
Aborted (core dumped)
$ gcc-4.8 -m32 -O3 small.c
$ a.out
0
Aborted (core dumped)
$