Why doesn't GCC optimize out deletion of null pointers in C++?

Question

Consider a simple program:

int main() {
  int* ptr = nullptr;
  delete ptr;
}

With GCC (7.2), there is a call instruction regardi

Answer 1

First of all, I'll just agree with some previous answerers in that it's not a bug, and GCC may do as it pleases here. That said, I was wondering whether this means that some common and simple RAII code may be slower on GCC than Clang because a straightforward optimization is not done.

So I wrote a small test case for RAII:

struct A
{
    explicit A() : ptr(nullptr) {}
    A(A &&from)
        : ptr(from.ptr)
    {
        from.ptr = nullptr;
    }

    A &operator =(A &&from)
    {
        if ( &from != this )
        {
            delete ptr;
            ptr = from.ptr;
            from.ptr = nullptr;
        }
        return *this;
    }

    int *ptr;
};

A a1;

A getA2();

void setA1()
{
    a1 = getA2();
}

As you may see here, GCC does elide the second call to delete in setA1 (for the moved-from temporary that was created in the call to getA2). The first call is necessary for program correctness because a1 or a1.ptr may have been previously assigned to.

Obviously I would prefer more "rhyme and reason" – why is the optimization done sometimes but not always – but I'm not willing to sprinkle redundant if ( ptr != nullptr ) checks all over my RAII code just yet.