https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67947
Bug ID: 67947 Summary: wrong code at -O3 on x86_64-linux-gnu Product: gcc Version: 6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: su at cs dot ucdavis.edu Target Milestone: --- The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O3 in both 32-bit and 64-bit modes. This is a regression from 5.2.x. $ gcc-trunk -v Using built-in specs. COLLECT_GCC=gcc-trunk COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper Target: x86_64-pc-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 6.0.0 20151012 (experimental) [trunk revision 228712] (GCC) $ $ gcc-trunk -O2 small.c; ./a.out 0 0 0 $ gcc-5.2 -O3 small.c; ./a.out 0 0 0 $ $ gcc-trunk -O3 small.c $ ./a.out $ ---------------------------------- int printf (const char *, ...); int a; int main (int argc, char* argv[]) { int j, k, b = 0; if (argc == 0) b = 1; for (j = 0; j < 3; j++) for (k = 0; k < 1; k++) { printf ("%d\n", 0); if (b) for (k = -1; a;) ; } return 0; }