https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63189
--- Comment #2 from Breton M. Saunders <br...@mynah-software.com> --- I'm actually showing the same symptoms on Ubuntu 12.04 using virtual-box and gcc v4.6.3. Here are the details: bms20@medivh-lbo-vm:~/LboPlatforms/ti37XX$ uname -a Linux medivh-lbo-vm 3.8.0-44-generic #66~precise1-Ubuntu SMP Tue Jul 15 04:01:04 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux bms20@medivh-lbo-vm:~/LboPlatforms/ti37XX$ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) And a cut-and-paste of the run: bms20@medivh-lbo-vm:/tmp$ gcc -O2 test.c && ./a.out s1ref=7, s1=7 bms20@medivh-lbo-vm:/tmp$ gcc -O2 -ftree-vectorize test.c && ./a.out s1ref=7, s1=1 bms20@medivh-lbo-vm:/tmp$ gcc -O3 test.c && ./a.out s1ref=7, s1=1 bms20@medivh-lbo-vm:/tmp$
