[Bug tree-optimization/100050] New: missed optimization for dead code elimination at -O3 (vs. -O1, -Os, -O2)

[zhendong.su at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100050

            Bug ID: 100050
           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: ---

[598] % 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 20210412 (experimental) [master revision
46c47420a5f:66634f1d5eb:8f17d44ad986e0ae7e81c81179463000ee9d7f43] (GCC) 
[599] % 
[599] % gcctk -O1 -S -o O1.s small.c
[600] % gcctk -O3 -S -o O3.s small.c
[601] % 
[601] % wc O1.s O3.s
  19   44  412 O1.s
  35   77  683 O3.s
  54  121 1095 total
[602] % 
[602] % grep foo O1.s
[603] % grep foo O3.s
        call    foo
[604] % 
[604] % cat small.c
extern void foo(void);
static int *a[2];
int main() {
  int c = 0;
  for (; c < 2; c++)
    a[c] = &c;
  if (!a[0])
    foo();
  return 0;
}