// only be called with the same opcodes as are handled by opstore and opload.
func (c *ctxt9) opform(insn uint32) int {
	switch insn {
	default:
		c.ctxt.Diag("bad insn in loadform: %x", insn)
	case OPVCC(58, 0, 0, 0), // ld
		OPVCC(58, 0, 0, 1),        // ldu
		OPVCC(58, 0, 0, 0) | 1<<1, // lwa
		OPVCC(62, 0, 0, 0),        // std
		OPVCC(62, 0, 0, 1):        //stdu
		return DS_FORM