t.Errorf("r.WriteTo(errorWriterToTests[%d]) = _, %v, want _,%v", i, err, rw.expected)
		}
	}
}

func TestWriterReadFrom(t *testing.T) {
	ws := []func(io.Writer) io.Writer{
		func(w io.Writer) io.Writer { return onlyWriter{w} },
		func(w io.Writer) io.Writer { return w },
	}

	rs := []func(io.Reader) io.Reader{
		iotest.DataErrReader,
		func(r io.Reader) io.Reader { return r },
	}

	b := bytes.NewBuffer(nil)
	w := NewWriter(b)
	for i := 0; i < 5; i++ {
		_, err := w.Create("")
		if err != nil {
			t.Fatalf("Writer.Create failed: %s", err)
		}
	}
	if err := w.Close(); err != nil {
		t.Fatalf("Writer.Close failed: %s", err)
	}
	r, err := NewReader(bytes.NewReader(b.Bytes()), int64(b.Len()))
	if err != nil {
		t.Fatalf("NewReader failed: %s", err)
	}

	// EVEX: VCVTPD2DQ with Y suffix (VL=2).
	VCVTPD2DQY (BX), X20  // 62e1ff28e623
	VCVTPD2DQY (R11), X30 // 6241ff28e633
	// XED encoder uses EVEX.X=0 for these; most x86 tools use EVEX.X=1.
	// Either way is OK.
	VMOVQ SP, X20  // 62e1fd086ee4 or 62a1fd086ee4
	VMOVQ BP, X20  // 62e1fd086ee5 or 62a1fd086ee5
	VMOVQ R14, X20 // 62c1fd086ee6 or 6281fd086ee6

	if *debugGcc {
		fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(args, " "))
		os.Stderr.Write(stdin)
		fmt.Fprint(os.Stderr, "EOF\n")
	}
	stdout, stderr, ok := run(stdin, args)
	if *debugGcc {
		os.Stderr.Write(stdout)
		os.Stderr.Write(stderr)
	}
	if !ok {
		os.Stderr.Write(stderr)
		os.Exit(2)
	}
	return string(stdout), string(stderr)
}

	AND	$1, ZR                              // fb0340b2ff031b8a
	ANDW	$1, ZR                              // fb030032ff031b0a
	// TODO: this could have better encoding
	ANDW	$-1, R10                            // 1b0080124a011b0a
	AND	$8, R0, RSP                         // 1f007d92
	ORR	$8, R0, RSP                         // 1f007db2