The following source code
----
struct d {
  long b;

  d *e() {
    __atomic_load_n(&b, 0);
    return this;
  }
};

d *j;

void i();

void k() {
  auto l = j->e();
  if (l)
    i();
}
----
produces the following bit of assembly with -O3 on x86_64 (https://godbolt.org/z/G1ThvnMWP):
...
        mov     rdx, QWORD PTR [rax]
        test    rax, rax
        je      .L1
...

It first dereferences the address at RAX, and later checks whether RAX == 0. Since we already tried accessing memory at that address, the nullptr check seems redundant. Moreover, since the address happens to be of 'this' of variable j, it being equal to nullptr is UB anyway and may be assumed to be != nullptr?

Clang tests show the redundant test being present up to version 11 inclusive (https://godbolt.org/z/rT3ha4enb) and absent from version 12 onwards (https://godbolt.org/z/Gfb9EWMfq)