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 tangotests.vararg4;

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

struct S
{
    int i;
}

void func(...)
{
    S* sp = cast(S*)_argptr;
    assert(sp.i == 42);
}

void main()
{
    printf("1st:\n");
    {
    S s = S(42);
    func(s);
    }
    printf("ok\n");

    printf("2nd:\n");
    {
    func(S(42));
    }
    printf("ok\n");
}