parse.y:5499
static void
local_push(top)
    int top;
{
    struct local_vars *local;

    local = ALLOC(struct local_vars);
    local->prev = lvtbl;
    local->nofree = 0;
    local->cnt = 0;
    local->tbl = 0;
    local->dlev = 0;
    local->dyna_vars = ruby_dyna_vars;
    lvtbl = local;
    if (!top) {
	/* preserve reference for GC, but link should be cut. */
	rb_dvar_push(0, (VALUE)ruby_dyna_vars);
	ruby_dyna_vars->next = 0;
    }
}
