https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77855
Bug ID: 77855 Summary: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes) Product: gcc Version: 7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: su at cs dot ucdavis.edu Target Milestone: --- It is a regression from 6.2.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/7.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto --prefix=/usr/local/gcc-trunk --disable-bootstrap Thread model: posix gcc version 7.0.0 20161004 (experimental) [trunk revision 240755] (GCC) $ $ gcc-6.2 -O3 small.c; ./a.out 2 $ gcc-trunk -O2 small.c; ./a.out 2 $ $ gcc-trunk -O3 small.c; ./a.out 0 $ -------------------------------------------------- int a, b = 1, c, e, f, g, k, m, n, o; char d, h, i, j, l; void fn1 () { if (e) j = 1; if (f) L1: k = j | (a & l); for (;;) { __builtin_printf ("%d\n", d); if (d) break; for (; o; o--) for (; n;) for (; m; m++) ; goto L1; } } void fn2 () { d = 2; } void fn3 () { for (;;) { for (; b; b--) { fn2 (8); fn1 (); } g = h; c = i; break; } } int main () { fn3 (); return 0; }