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.

struct S {
    int a; int b; int c; int d = 7;
}
void test(int i) {
    S s = { 1, i };   // q.a = 1, q.b = i, q.c = 0, q.d = 7
    assert(s.a == 1);
    assert(s.b == i);
    assert(s.c == 0); // line 8
    assert(s.d == 7);
}
void main() {
    test(42);
}