https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87132
Bug ID: 87132 Summary: Gcc miscompiles at -O2 on valid code Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: helloqirun at gmail dot com Target Milestone: --- It seems to be a recent regression starting from r263875 (need double check). $ gcc-trunk -v Using built-in specs. COLLECT_GCC=gcc-trunk COLLECT_LTO_WRAPPER=/home/absozero/trunk/root-gcc/libexec/gcc/x86_64-pc-linux-gnu/9.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc/configure --prefix=/home/absozero/trunk/root-gcc --enable-languages=c,c++ --disable-werror --enable-multilib Thread model: posix gcc version 9.0.0 20180828 (experimental) [trunk revision 263917] (GCC) $ gcc-trunk abc.c ; ./a.out 0 $ gcc-trunk -O2 abc.c ; ./a.out 4 $ cat abc.c int printf(const char *, ...); int a, b; short c; char d; int main() { int e[] = {4, 4, 4, 4, 4, 4, 4, 4, 4}; d = 8; for (; d; d--) { a = 0; for (; a <= 8; a++) { c = e[1]; e[d] = b; } } printf("%d\n", c); }