https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99987
Bug ID: 99987 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: --- [748] % 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 20210409 (experimental) [master revision 96292c3e343:4e14cad25b9:019a922063f26784d5a070d9198a1f937b8a8343] (GCC) [749] % [749] % [749] % gcctk -O2 -S -o O2.s small.c [750] % gcctk -O3 -S -o O3.s small.c [751] % [751] % wc O2.s O3.s 68 150 961 O2.s 89 195 1278 O3.s 157 345 2239 total [752] % [752] % grep foo O2.s [753] % grep foo O3.s call foo [754] % [754] % cat small.c extern void foo(void); static int a[8] = {0,0,0,0,0,0,0,0}; int b, c, j; static int *e(int k) { if (k && b) j = 0; while (j) if (!k) foo(); return 0; } static void d() { long g; unsigned h = 8; if (b) for (g = 2; 1; g--) { int i = 0; h--; c = (a[g] == (&i != e(h))); } } void f() { d(); }