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.

// testcase from bug #199

struct Color {
    uint c;

}

struct Vertex {
    Color c;
}

void main() {
    Color c = {0xffffffff};

    auto v = Vertex(c);

    assert(v.c.c == 0xffffffff);  // fails in LDC
}