http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59715
Bug ID: 59715 Summary: wrong code at -Os and above on x86_64-linux-gnu Product: gcc Version: 4.9.0 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 4.8.x and 4.7.x) miscompiles the following code on x86_64-linux at -Os and above in both 32-bit and 64-bit modes. This is a regression from 4.6.x. $ 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 --prefix=/usr/local/gcc-trunk --enable-languages=c,c++ --disable-werror --enable-multilib Thread model: posix gcc version 4.9.0 20140107 (experimental) [trunk revision 206387] (GCC) $ $ gcc-trunk -O1 small.c; a.out 0 $ gcc-4.6 -Os small.c; a.out 0 $ gcc-trunk -Os small.c; a.out 2 $ gcc-4.8 -Os small.c; a.out 2 $ gcc-4.7 -Os small.c; a.out 2 $ ---------------------------------- int printf (const char *, ...); int a = 2, b; int main () { int c; if (!b) { b = a; c = a == 0 ? 1 : 1 % a; if (c) b = 0; } printf ("%d\n", b); return 0; }