https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80622
Bug ID: 80622 Summary: wrong code at -O1 and above in both 32-bit and 64-bit modes on x86_64-linux-gnu Product: gcc Version: 7.0.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: chengniansun at gmail dot com Target Milestone: --- $ 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/8.0.0/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 8.0.0 20170503 (experimental) [trunk revision 247550] (GCC) $ gcc-trunk small.c -O3 ; ./a.out 0 $ gcc-trunk small.c -O3 -m32 ; ./a.out 0 $ gcc-trunk small.c -O1 -m32 ; ./a.out 0 $ gcc-trunk small.c -O0 -m32 ; ./a.out 4 $ $ cat small.c int printf(const char *, ...); struct S2 { int f2; char f4; int f5; char f6; } a; int main() { struct S2 b[][1] = {3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 0, 3, 4, 3, 4, 7, 7, 3, 5, 0, 3, 4, 7, 7, 3, 5, 0, 3, 4, 3, 4, 7, 7, 3, 5, 0, 3, 4, 7, 7, 3, 5, 0, 3, 4}; a = b[4][0]; b[4][0].f4 &printf("%d\n", a.f6); return 0; } $ $ gcc-5.4 small.c -O3 -m32 ; ./a.out 4 $