[Bug tree-optimization/71343] missed optimization (can't "prove" shift and multiplication equivalence)

[SztfG at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71343

--- Comment #2 from SztfG at yandex dot ru ---
This also not optimized by gcc:

unsigned int test3(unsigned int a , unsigned int b)
{
  return (a << 2) + (b << 2) ==  (a + b) << 2;
}

but this works:

unsigned int test4(unsigned int a , unsigned int b)
{
  return (a * 4) + (b * 4) == (a + b) * 4;
}

result:
        movl    $1, %eax
        ret

Distributive property also should work with binary shifts.