https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100220
Bug ID: 100220 Summary: missed optimization for dead code elimination at -O3 (vs. -O1, -Os, -O2) Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: ipa Assignee: unassigned at gcc dot gnu.org Reporter: zhendong.su at inf dot ethz.ch CC: marxin at gcc dot gnu.org Target Milestone: --- [638] % 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/12.0.0/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 12.0.0 20210422 (experimental) [master revision 3cf04d1afa8:0e51007a40c:d42088e453042f4f8ba9190a7e29efd937ea2181] (GCC) [639] % [639] % gcctk -O1 -S -o O1.s small.c [640] % gcctk -O3 -S -o O3.s small.c [641] % [641] % wc O1.s O3.s 62 135 857 O1.s 93 200 1337 O3.s 155 335 2194 total [642] % [642] % grep foo O1.s [643] % grep foo O3.s call foo [644] % [644] % cat small.c extern void foo(void); int b, c, d, e, *h; static int *f = &e; static int a() { return 1; } static void g() { if (!*f) for (; 1; d++) ; foo(); } static void i() { int j, l = 0, k[24] = {0}, *m[2] = {&k[4], &l}, n[27]; h = n; if (a() & n[0]) for (; c; c--) ; int p[8]; h = p; p[0] && (h = &j); e = 0; } static void o() { int *q, **r = &q, ***s[1]; s[0] = &r; i(); g(); } int main() { if (b) o(); return 0; }