[Bug tree-optimization/99835] New: missed optimization for dead code elimination at -O3 (vs. -O1)

[zhendong.su at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99835

            Bug ID: 99835
           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: ---

[558] % 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 20210330 (experimental) [master revision
8aac913adfc:ff4ebc2f17c:65374af219f9c5c594951a07e766fe70c1136a1f] (GCC) 
[559] % 
[559] % gcctk -O1 -S -o O1.s small.c
[560] % gcctk -O3 -S -o O3.s small.c
[561] % 
[561] % wc O1.s O3.s
  23   45  420 O1.s
  35   66  615 O3.s
  58  111 1035 total
[562] % 
[562] % grep foo O1.s
[563] % grep foo O3.s
        jmp     foo
[564] % 
[564] % cat small.c
extern void foo(void);
static int a, d;
void b();
static int c() {
  foo();
  b();
}
void b() {
  while (d) {
    if (!a)
      break;
    c();
  }
}
int main() {
  b();
  return 0;
}