https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70602
Bug ID: 70602 Summary: wrong code at -O1 and above on x86_64-linux-gnu in 32-bit mode (and at -Os only in 64-bit mode) Product: gcc Version: 6.0 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: --- The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O1 and above in the 32-bit mode and at -Os only in the 64-bit mode. This is a regression from 5.3.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-source-trunk/configure --enable-languages=c,c++,lto --prefix=/usr/local/gcc-trunk --disable-bootstrap Thread model: posix gcc version 6.0.0 20160408 (experimental) [trunk revision 234826] (GCC) $ $ gcc-trunk -m32 -O0 small.c; ./a.out $ gcc-5.3 -m32 -O1 small.c; ./a.out $ $ gcc-trunk -m32 -O1 small.c $ ./a.out Segmentation fault (core dumped) $ ----------------------------------------- #pragma pack(1) struct S0 { int f0:1; int f1:20; }; int a, b, c; int main () { for (; a < 1; a++) { struct S0 e[] = { {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9} }; b = b || e[0].f0; c = e[0].f1; } return 0; }