https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70127
Bug ID: 70127 Summary: wrong code on x86_64-linux-gnu at -O3 in 32-bit and 64-bit modes Product: gcc Version: 6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: web Assignee: unassigned at gcc dot gnu.org Reporter: chengniansun at gmail dot com Target Milestone: --- The following code is miscompiled by the trunk, gcc-4.7 and gcc-4.8 at -O3 in both 32-bit and 64-bit modes on x86_64-linux-gnu. $: 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-source-trunk/configure --enable-languages=c,c++,lto --prefix=/usr/local/gcc-trunk --disable-bootstrap Thread model: posix gcc version 6.0.0 20160307 (experimental) [trunk revision 234022] (GCC) $: $: gcc-trunk -O3 small.c ; ./a.out 0 $: gcc-4.7 -O3 small.c ; ./a.out 0 $: gcc-4.8 -O3 small.c ; ./a.out 0 $: gcc-trunk -O0 small.c ; ./a.out 1 $: cat small.c int printf(const char *, ...); struct S0 { int f0; signed f1 : 2; } a[1], c = {5, 1}, d; short b; int main() { for (; b <= 0; b++) { struct S0 e = {1, 1}; d = e = a[0] = c; } printf("%d\n", a[0].f1); return 0; } $: