https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100112
Bug ID: 100112 Summary: missed optimization for dead code elimination at -O3, -Os (vs. -O1, -O2) Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: zhendong.su at inf dot ethz.ch Target Milestone: --- [545] % gcctk -v Using built-in specs. COLLECT_GCC=gcctk COLLECT_LTO_WRAPPER=/local/suz-local/software/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/11.0.1/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-trunk/configure --disable-bootstrap --prefix=/local/suz-local/software/local/gcc-trunk --enable-languages=c,c++ --disable-werror --enable-multilib --with-system-zlib Thread model: posix Supported LTO compression algorithms: zlib gcc version 11.0.1 20210416 (experimental) [master revision 89c863488bc:10ed13839be:76c7e7d6b003a17d183d0571bf9b34c691819d25] (GCC) [546] % [546] % gcctk -O1 -S -o O1.s small.c [547] % gcctk -O3 -S -o O3.s small.c [548] % [548] % wc O1.s O3.s 17 38 365 O1.s 37 78 633 O3.s 54 116 998 total [549] % [549] % grep foo O1.s [550] % grep foo O3.s call foo [551] % [551] % cat small.c extern void foo(void); static int e, *a = &e, b, *c = &b; static int d(int f, int i) { if (f ^ i) foo(); } int main() { int **g = &c; (*a)++; *g = c; d(1, c != 0); return 0; }