for i, v := range b.ControlValues() {
			if v.Op == OpCopy {
				b.ReplaceControl(i, v.Args[0])
			}
		}
	}

	// Update named values.
	for _, name := range f.Names {
		values := f.NamedValues[*name]
		for i, v := range values {
			if v.Op == OpCopy {
				values[i] = v.Args[0]
			}
		}
	}
}

// copySource returns the (non-copy) op which is the
// ultimate source of v.  v must be a copy op.