https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100221
Bug ID: 100221 Summary: missed optimization for dead code elimination at -O3 (vs. -O1, -Os, -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: --- [551] % 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) [552] % [552] % gcctk -O1 -S -o O1.s small.c [553] % gcctk -O3 -S -o O3.s small.c [554] % [554] % wc O1.s O3.s 49 100 693 O1.s 73 151 1072 O3.s 122 251 1765 total [555] % [555] % grep foo O1.s [556] % grep foo O3.s call foo [557] % [557] % cat small.c extern void foo(void); int a, b; static int c; static void f() { while (a) for (; b; b--) ; } void i() { if (c) foo(); int *g = &c; { int **h[1] = {&g}; f(); } } int main() { i(); return 0; }