Test case:

char[] foo(char[] source) { return ""; }
const v = "bar";
const r = foo(v);

Result:
Error: cannot evaluate foo(cast(char[])v) at compile time

This works in D2 because of changes to Cast in constfold.c. LDC backported the changes by adding this code from the D2 frontend:

    if (e1->op == TOKstring)
    {
	if (tb->ty == Tarray && typeb->ty == Tarray &&
	    tb->nextOf()->size() == typeb->nextOf()->size())
	{
	    return expType(to, e1);
	}
    }