[Bug c/47418] New: warning: array subscript is above array bounds at O2 with sin6_addr

[dpmcgee at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47418

           Summary: warning: array subscript is above array bounds at O2
                    with sin6_addr
           Product: gcc
           Version: 4.5.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: dpmcgee@gmail.com
              Host: x86_64-unknown-linux-gnu
            Target: x86_64-unknown-linux-gnu
             Build: x86_64-unknown-linux-gnu


Created attachment 23083
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23083
Preprocessed test case

Originally from http://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=43491

Preprocessed stripped test case (<100 lines) attached.

Only occurs on x86_64. At -O1 or -O0 this does not warn. It obviously also
warns at -O3.

$ pacman -Q glibc
glibc 2.13-1
$ uname -a
Linux galway 2.6.36-ARCH #1 SMP PREEMPT Sat Jan 8 14:15:27 CET 2011 x86_64
Intel(R) Core(TM)2 Quad CPU Q9400 @ 2.66GHz GenuineIntel GNU/Linux
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.5.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/src/gcc-4.5.2/configure --prefix=/usr
--enable-languages=c,c++,fortran,objc,obj-c++,ada --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--enable-gnu-unique-object --enable-lto --enable-plugin --enable-gold
--with-plugin-ld=ld.gold --disable-multilib --disable-libstdcxx-pch
--with-system-zlib --with-ppl --with-cloog
--with-cloog-include=/usr/include/cloog-ppl --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
Thread model: posix
gcc version 4.5.2 (GCC) 


$ gcc -O2 -Wall -c ftp-stripped.i 
ftp-stripped.i: In function ‘main’:
ftp-stripped.i:86:30: warning: array subscript is above array bounds
ftp-stripped.i:86:22: warning: array subscript is above array bounds
ftp-stripped.i:86:14: warning: array subscript is above array bounds
ftp-stripped.i:86:6: warning: array subscript is above array bounds
ftp-stripped.i:85:28: warning: array subscript is above array bounds
ftp-stripped.i:85:20: warning: array subscript is above array bounds
ftp-stripped.i:85:13: warning: array subscript is above array bounds
ftp-stripped.i:85:6: warning: array subscript is above array bounds



On i686, no warnings at any optimization level occur.

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-pc-linux-gnu/4.5.2/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: /build/src/gcc-4.5.2/configure --prefix=/usr
--enable-languages=c,c++,fortran,objc,obj-c++,ada --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--enable-gnu-unique-object --enable-lto --enable-plugin --enable-gold
--with-plugin-ld=ld.gold --disable-multilib --disable-libstdcxx-pch
--with-system-zlib --with-ppl --with-cloog
--with-cloog-include=/usr/include/cloog-ppl --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
Thread model: posix
gcc version 4.5.2 (GCC)