Another shot at fixing the issues with (constant) struct literals and their addresses. See DMD2682, #218, #324. The idea is to separate the notion of const from 'this variable can always be replaced with its initializer' in the frontend. To do that, I introduced Declaration::isSameAsInitializer, which is overridden in VarDeclaration to return false for constants that have a struct literal initializer. So {{{ const S s = S(5); void foo() { auto ps = &s; } // is no longer replaced by void foo() { auto ps = &(S(5)); } }}} To make taking the address of a struct constant with a struct-initializer outside of function scope possible, I made sure that AddrExp::optimize doesn't try to run the argument's optimization with WANTinterpret - that'd again replace the constant with a struct literal temporary.

module union5;

union S
{
    T t;
    U u;
    uint i;
    struct {
        ushort sl,sh;
    }
}

struct T
{
    int i;
}

struct U
{
    float f;
}

void main()
{
    S s;
    assert(s.t.i == 0);
    assert(s.u.f == 0);
    s.t.i = -1;
    assert(s.i == 0xFFFF_FFFF);
    float f = 3.1415;
    s.u.f = f;
    uint pi = *cast(uint*)&f;
    assert(s.i == pi);
    assert(s.sl == (pi&0xFFFF));
    assert(s.sh == (pi>>>16));
}