[Bug tree-optimization/100315] New: missed optimization for dead code elimination at -O3, -O2 (vs. -O1, -Os)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100315

            Bug ID: 100315
           Summary: missed optimization for dead code elimination at -O3,
                    -O2 (vs. -O1, -Os)
           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: ---

[583] % 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 20210428 (experimental) [master revision
852dd866e2f:9b04e5b2651:b81e2d5e76a6bcc71f45b122e8b5538ddb7ebf4c] (GCC) 
[584] % 
[584] % gcctk -O1 -S -o O1.s small.c
[585] % gcctk -O3 -S -o O3.s small.c
[586] % 
[586] % wc O1.s O3.s
 14  30 303 O1.s
 18  39 364 O3.s
 32  69 667 total
[587] % 
[587] % grep foo O1.s
[588] % grep foo O3.s
        call    foo
[589] % 
[589] % cat small.c
extern void foo(void);
static int a;
static void b(int c) {
  if (c) {
    foo();
    while (1)
      ;
  }
}
void d() {
  int e = 0;
  while (1) {
    b(a);
    e++;
  }
}