Thread:
http://forum.dlang.org/thread/khdhvzfdfljbtlyfqocw@forum.dlang.org#post-khdhvzfdfljbtlyfqocw:40forum.dlang.org

When compiled with -O -inline:
--------
struct S
{
    int[0] a;

    void do_it()
    {
        foo(a);
    }
}

void foo(Args...)(Args args)
{
    //foreach(arg; args)
    //    if (arg.ptr == null)
    //        return;

    bar(args);
}

void bar(Args...)(Args args)
{
    foreach(arg; args)
        if (arg.ptr == null)
            return;
}

void main()
{}
--------
Produces:
main.d(11): Error: variable _param_0 used before set
--------

Possibly the compiler optimizes out a's initialization, since it is an empty static array.

Code is glitchy: Not only does the bug appear only in bar (and not foo), un-commenting the code in foo will *fix* the call in bar...