Update comments now that LLVM PR3861 has been fixed. However, since conditionally removing the workaround makes the ABI dependent on LLVM version, I reconsidered that. (The same revision of LDC compiling for the same target should probably produce code that follows the same ABI, right?)

module union4;

union U {
    struct { float x,y,z; }
    float[3] xyz;
}

void main() {
    const float[3] a = [1f,2,3];
    U u = U(1,2,3);
    assert(u.xyz == a);
    assert(u.x == 1);
    assert(u.y == 2);
    assert(u.z == 3);
}