I don't think there's anything wrong with the testcase. The -O2 result is wrong.
[reg...@gamow ~]$ current-gcc -v Using built-in specs. COLLECT_GCC=current-gcc COLLECT_LTO_WRAPPER=/uusoc/exports/scratch/regehr/z/compiler-install/gcc-r164319-install/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.6.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../configure --with-libelf=/usr/local --enable-lto --prefix=/home/regehr/z/compiler-install/gcc-r164319-install --program-prefix=r164319- --enable-languages=c,c++ Thread model: posix gcc version 4.6.0 20100915 (experimental) (GCC) [reg...@gamow ~]$ current-gcc -O1 small.c -o small [reg...@gamow ~]$ ./small 1 [reg...@gamow ~]$ current-gcc -O2 small.c -o small [reg...@gamow ~]$ ./small 0 [reg...@gamow ~]$ cat small.c int printf(const char *format, ...); static int g_7; static int *volatile g_6 = &g_7; static int func_53(int *p_58) { return *p_58; } int main(void) { *g_6 = 1; printf("%d\n", func_53(&g_7)); return 0; } -- Summary: possible wrong code bug Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: regehr at cs dot utah dot edu GCC build triplet: x86_64-unknown-linux-gnu GCC host triplet: x86_64-unknown-linux-gnu GCC target triplet: x86_64-unknown-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45687