[Bug tree-optimization/100113] New: missed optimization for dead code elimination at -O3 (vs. -O1)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100113

            Bug ID: 100113
           Summary: missed optimization for dead code elimination at -O3
                    (vs. -O1)
           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: ---

[584] % 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 20210416 (experimental) [master revision
89c863488bc:10ed13839be:76c7e7d6b003a17d183d0571bf9b34c691819d25] (GCC) 
[585] % 
[585] % gcctk -O1 -S -o O1.s small.c
[586] % gcctk -O3 -S -o O3.s small.c
[587] % 
[587] % wc O1.s O3.s
  84  185 1140 O1.s
 120  254 1768 O3.s
 204  439 2908 total
[588] % 
[588] % grep foo O1.s
[589] % grep foo O3.s
        call    foo
[590] % 
[590] % cat small.c
extern void foo(void);
int a, b, d, *c = &a, e, k;
static int f(int *h, int i, int **l) {
  for (b = 0; b < 1; b++) {
    int *f = &d;
    for (; d < 1; d++)
      f = c;
    if (f != &a)
      __builtin_abort();
    if (k)
      *c = 0;
  }
  *c = 0;
  return **l;
}
int main() {
  int *j = &b;
  if (!f(j, e, &j))
    foo();
  return 0;
}