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 mini.assign1;

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

struct X
{
    int a;
    alias a b;
}
void main()
{
    X e = void;
    e.a = e.b = 5;
    printf("%d - %d\n", e.a, e.b);
    assert(e.a == 5);
    assert(e.a == e.b);
}