[Bug tree-optimization/100162] New: missed optimization for dead code elimination at -O3 (vs. -O2)

[zhendong.su at inf dot ethz.ch via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100162

            Bug ID: 100162
           Summary: missed optimization for dead code elimination at -O3
                    (vs. -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: ---

[720] % 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 20210420 (experimental) [master revision
67378cd63d6:5e36407d599:250f234988b6231669a720c52101d3686d645072] (GCC) 
[721] % 
[721] % gcctk -O2 -S -o O2.s small.c
[722] % gcctk -O3 -S -o O3.s small.c
[723] % 
[723] % wc O2.s O3.s
  52  119  923 O2.s
  70  150 1143 O3.s
 122  269 2066 total
[724] % 
[724] % grep foo O2.s
[725] % grep foo O3.s
        call    foo
[726] % 
[726] % cat small.c
extern void foo(void);
int printf(const char *, ...);
int a, b, c[5][1];
int main() {
  for (a = 0; a < 5; a++)
    c[a][b] = 2;
  if ((b || 0) / c[0][0])
    foo();
  printf("checksum=0");
  return 0;
}