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 union3;

union vec3
{
    struct { float x,y,z; }
    float[3] xyz;
}

void main()
{
    vec3 v;
    assert(&v.y is &v.xyz[1]);
}