Make == for associative arrays test for equality, not identity. _aaEq was added to runtime/internal/aaA.d which forwards to TypeInfo_AssociativeArray.equals in genobj.d. On the codegen side, DtoAAEquals was added to gen/aa.cpp and is called from EqualExp::toElem in gen/toir.cpp. I assume that the frontend will produce an error if == is used on associative arrays of different type. This fixes DMD bug 1429.

module interface3;

extern(C) int printf(char*,...);

interface I
{
    void func();
}

class C : I
{
    int i = 42;
    override void func()
    {
        printf("hello %d from %p\n", i, this);
        i++;
    }
}

void main()
{
    auto c = new C;
    {c.func();}
    {
        I i = c;
        {i.func();}
    }
    {printf("final %d\n", c.i);}
    {assert(c.i == 44);}
}