block3.go

func newCipher(key []byte) (cipher.Block, error) {
	if !supportsAES {
		return newCipherGeneric(key)
	}
	n := len(key) + 28
	c := aesCipherAsm{aesCipher{make([]uint32, n), make([]uint32, n)}}
    ...

	if supportsAES && supportsGFMUL {
		return &aesCipherGCM{c}, nil
	}
	return &c, nil
}