https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78428
Bug ID: 78428 Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu in 64-bit mode Product: gcc Version: unknown 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: --- It also affects 5.x and 6.x, and is a regression from 4.9.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 20161119 (experimental) [trunk revision 242621] (GCC) $ $ gcc-trunk -Os small.c; ./a.out $ gcc-4.9 -O2 small.c; ./a.out $ $ gcc-trunk -O2 small.c $ timeout -s 9 10 ./a.out Killed $ ----------------------------------------------- int printf (const char *, ...); struct S0 { int f2; int:16; int f4:18; }; int a = 5, c, e, i; struct S0 b = { 2, 0 }; static struct S0 g[] = { { 7, 2 } }; int f = 1, h; int main () { for (; a; a--) { volatile struct S0 *j = &b; L1: if (!f || h) { printf ("%d\n", e); goto L1; } for (c = 0; c < 1; c++) i = 0; for (; i < 1; i++) *j = g[0]; } return 0; }