<p>
If <code>a</code> is not a map:
</p>
<ul>
	<li>the index <code>x</code> must be of integer type or an untyped constant</li>
	<li>a constant index must be non-negative and
	    <a href="#Representability">representable</a> by a value of type <code>int</code></li>
	<li>a constant index that is untyped is given type <code>int</code></li>
	<li>the index <code>x</code> is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,

	// AVX512GATHER index/index #UD cases.
	VPGATHERQQ (BP)(X2*2), K1, X2   // ERROR "index and destination registers should be distinct"
	VPGATHERQQ (BP)(Y15*2), K1, Y15 // ERROR "index and destination registers should be distinct"
	VPGATHERQQ (BP)(Z20*2), K1, Z20 // ERROR "index and destination registers should be distinct"
	VPGATHERDQ (BP)(X2*2), K1, X2   // ERROR "index and destination registers should be distinct"

		for i := range b {
			idx := Index(b[i:], q[:j])
			if idx != -1 {
				t.Fatalf("Index(b[%d:], q[:%d])=%d, want -1\n", i, j, idx)
			}
		}
		q[j-1] = 0
	}

	// Test differing alignments and sizes of q which always end on a page boundary.
	q[len(q)-1] = 1 // difference is only found on the last byte
	for j := 0; j < len(q); j++ {
		for i := range b {
			idx := Index(b[i:], q[j:])
			if idx != -1 {

		}
		if r == tr {
			continue
		}
		return false
	}

	// One string is empty. Are both?
	return len(s) == len(t)
}

// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
func Index(s, sep []byte) int {
	n := len(sep)
	switch {
	case n == 0:
		return 0
	case n == 1:
		return IndexByte(s, sep[0])
	case n == len(s):

}

func bmIndexRuneASCII(index func([]byte, rune) int) func(b *testing.B, n int) {
	return func(b *testing.B, n int) {
		buf := bmbuf[0:n]
		buf[n-1] = 'x'
		for i := 0; i < b.N; i++ {
			j := index(buf, 'x')
			if j != n-1 {
				b.Fatal("bad index", j)
			}
		}
		buf[n-1] = '\x00'
	}
}

func bmIndexRune(index func([]byte, rune) int) func(b *testing.B, n int) {

		f.walk(n.Elts, ctxExpr, visit)
	case *ast.ParenExpr:
		f.walk(&n.X, context, visit)
	case *ast.SelectorExpr:
		f.walk(&n.X, ctxSelector, visit)
	case *ast.IndexExpr:
		f.walk(&n.X, ctxExpr, visit)
		f.walk(&n.Index, ctxExpr, visit)
	case *ast.SliceExpr:
		f.walk(&n.X, ctxExpr, visit)
		if n.Low != nil {
			f.walk(&n.Low, ctxExpr, visit)
		}
		if n.High != nil {
			f.walk(&n.High, ctxExpr, visit)
		}

	//	// +godefs map struct_in_addr6 [16]byte
	//
	for _, g := range f.Comments {
		for _, c := range g.List {
			i := strings.Index(c.Text, "+godefs map")
			if i < 0 {
				continue
			}
			s := strings.TrimSpace(c.Text[i+len("+godefs map"):])
			i = strings.Index(s, " ")
			if i < 0 {
				fmt.Fprintf(os.Stderr, "invalid +godefs map comment: %s\n", c.Text)
				continue
			}

// Unlike a [Buffer], a Reader is read-only and supports seeking.
// The zero value for Reader operates like a Reader of an empty slice.
type Reader struct {
	s        []byte
	i        int64 // current reading index
	prevRune int   // index of previous rune; or < 0
}

// Len returns the number of bytes of the unread portion of the
// slice.
func (r *Reader) Len() int {
	if r.i >= int64(len(r.s)) {
		return 0
	}

	ctxt.IsAsm = true
	ctxt.Pkgpath = *flags.Importpath
	switch *flags.Spectre {
	default:
		log.Printf("unknown setting -spectre=%s", *flags.Spectre)
		os.Exit(2)
	case "":
		// nothing
	case "index":
		// known to compiler; ignore here so people can use
		// the same list with -gcflags=-spectre=LIST and -asmflags=-spectrre=LIST
	case "all", "ret":
		ctxt.Retpoline = true
	}

	ctxt.Bso = bufio.NewWriter(os.Stdout)

	if !ok || u.Op != token.AND {
		return false
	}
	index, ok := u.X.(*ast.IndexExpr)
	if !ok {
		return false
	}

	addr := ""
	deref := ""
	if p.isVariable(index.X) {
		addr = "&"
		deref = "*"
	}

	fmt.Fprintf(sb, "_cgoIndex%d := %s%s; ", i, addr, gofmtPos(index.X, index.X.Pos()))
	origX := index.X
	index.X = ast.NewIdent(fmt.Sprintf("_cgoIndex%d", i))
	if deref == "*" {