https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99834
Bug ID: 99834 Summary: missed optimization for dead code elimination at -O3 (vs. -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: --- [590] % 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 20210330 (experimental) [master revision 8aac913adfc:ff4ebc2f17c:65374af219f9c5c594951a07e766fe70c1136a1f] (GCC) [591] % [591] % gcctk -O2 -S -o O2.s small.c [592] % gcctk -O3 -S -o O3.s small.c [593] % [593] % wc O2.s O3.s 43 90 704 O2.s 61 126 950 O3.s 104 216 1654 total [594] % [594] % grep foo O2.s [595] % grep foo O3.s call foo call foo [596] % [596] % cat small.c extern void foo(void); static int a, b, c; static int d() { for (a = 0; a < 1; a++) b = 1; for (; b; b--) for (; c; c--) ; return 0; } static void e() { if (d()) foo(); } int main() { e(); e(); return 0; }