Compiling the following code snippet:
int main(int argc, char **argv)
{
int i;
int asize = 3;
int array[3];
for (i = asize - 1; i < asize; i++)
array[i] = 42;
for (i = 0; i < asize; i++)
printf("%i\n", array[i]);
}
with "gcc -O -Wunreachable-code gccbug.c" shows the following warning message:
gccbug.c: In function 'main':
gccbug.c:8: warning: will never be executed
(Where line 8 is the body of the first for-loop, array[i] = 42;)
Though, array[2] is set to 42, as the later printf shows when executing.
When replacing the "- 1" of line 7 with an higher value, e.g. "- 2", the
warning disappears. Not passing "-O" to the compiler lets the warning
disappear, too.
I tested it with two versions of gcc. The first:
Using built-in specs.
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.3.4/work/gcc-4.3.4/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.3.4
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.3.4
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.3.4/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.3.4/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
--disable-fixed-point --enable-nls --without-included-gettext
--with-system-zlib --disable-checking --disable-werror --enable-secureplt
--enable-multilib --enable-libmudflap --disable-libssp --enable-libgomp
--disable-libgcj --enable-languages=c,c++,treelang,fortran --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.3.4 p1.0,
pie-10.1.5'
Thread model: posix
gcc version 4.3.4 (Gentoo 4.3.4 p1.0, pie-10.1.5)
The second:
Using built-in specs.
Target: arm-elf
Configured with: /tmp/gcc.ndS8/gcc-4.4.1/configure --enable-languages=c
--with-mpfr=/usr --without-headers --target=arm-elf --prefix=/usr/local/arm-elf
--with-local-prefix=/usr/local/arm-elf --disable-werror --disable-multilib
--disable-shared --disable-nls --disable-libssp --with-arch=armv4t
--with-cpu=arm7tdmi-s
Thread model: single
gcc version 4.4.1 (GCC)
The warning appears with both gcc versions.
--
Summary: "warning: will never be executed" about code which is
executed with "-Wunreachable-code"
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: agraf at znc dot in
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42476
