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.sync2;

class Lock
{
}

const Lock lock;

static this()
{
    lock = new Lock;
}

void main()
{
    size_t id;
    synchronized(lock) id = 2;
}