[Bug tree-optimization/86732] Potential nullptr dereference does not propagate knowledge about the pointer

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86732

--- Comment #1 from Antony Polukhin <antoshkka at gmail dot com> ---
Probably a more fair example< without taking an address of a reference:

static const int* get_if(const int* v) {
    if (v && *v == 0) return v;
    return nullptr;
}

int example(const int* a) {
    return *get_if(a);
}

GCC produces the same suboptimal assembly:

_Z7examplePKi:
  test rdi, rdi
  je .L2
  mov eax, DWORD PTR [rdi]
  test eax, eax
  jne .L2
  xor eax, eax
  ret
_Z7examplePKi.cold.0:
.L2:
  mov eax, DWORD PTR ds:0
  ud2


While Clang just generates:
_Z7examplePKi: # @_Z7examplePKi
  mov eax, dword ptr [rdi]
  ret