instAlt := p.Inst[*p_A_Alt]
			if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
				p_A_Alt, p_A_Other = p_A_Other, p_A_Alt
				instAlt = p.Inst[*p_A_Alt]
				if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
					continue
				}
			}
			instOther := p.Inst[*p_A_Other]
			// Analyzing both legs pointing to Alts is for another day

}

// An InstOp is an instruction opcode.
type InstOp uint8

const (
	InstAlt InstOp = iota
	InstAltMatch
	InstCapture
	InstEmptyWidth
	InstMatch
	InstFail
	InstNop
	InstRune
	InstRune1
	InstRuneAny
	InstRuneAnyNotNL
)

var instOpNames = []string{
	"InstAlt",
	"InstAltMatch",
	"InstCapture",
	"InstEmptyWidth",
	"InstMatch",
	"InstFail",
	"InstNop",

	if f1.i == 0 {
		return f2
	}
	if f2.i == 0 {
		return f1
	}

	f := c.inst(InstAlt)
	i := &c.p.Inst[f.i]
	i.Out = f1.i
	i.Arg = f2.i
	f.out = f1.out.append(c.p, f2.out)
	f.nullable = f1.nullable || f2.nullable
	return f
}

func (c *compiler) quest(f1 frag, nongreedy bool) frag {
	f := c.inst(InstAlt)
	i := &c.p.Inst[f.i]
	if nongreedy {
		i.Arg = f1.i
		f.out = makePatchList(f.i << 1)

	d := &q.dense[j]
	d.t = nil
	d.pc = pc
	q.sparse[pc] = uint32(j)

	i := &m.p.Inst[pc]
	switch i.Op {
	default:
		panic("unhandled")
	case syntax.InstFail:
		// nothing
	case syntax.InstAlt, syntax.InstAltMatch:
		t = m.add(q, i.Out, pos, cap, cond, t)
		pc = i.Arg
		goto Again
	case syntax.InstEmptyWidth:
		if cond.match(syntax.EmptyOp(i.Arg)) {
			pc = i.Out
			goto Again
		}

			continue
		}
	Skip:

		inst := &re.prog.Inst[pc]

		switch inst.Op {
		default:
			panic("bad inst")
		case syntax.InstFail:
			panic("unexpected InstFail")
		case syntax.InstAlt:
			// Cannot just
			//   b.push(inst.Out, pos, false)
			//   b.push(inst.Arg, pos, false)
			// If during the processing of inst.Out, we encounter
			// inst.Arg via another path, we want to process it then.

		{"Flags", Type, 0},
		{"FoldCase", Const, 0},
		{"Inst", Type, 0},
		{"Inst.Arg", Field, 0},
		{"Inst.Op", Field, 0},
		{"Inst.Out", Field, 0},
		{"Inst.Rune", Field, 0},
		{"InstAlt", Const, 0},
		{"InstAltMatch", Const, 0},
		{"InstCapture", Const, 0},
		{"InstEmptyWidth", Const, 0},
		{"InstFail", Const, 0},
		{"InstMatch", Const, 0},
		{"InstNop", Const, 0},

pkg regexp/syntax, const ErrMissingRepeatArgument ErrorCode
pkg regexp/syntax, const ErrTrailingBackslash ErrorCode
pkg regexp/syntax, const FoldCase Flags
pkg regexp/syntax, const InstAlt InstOp
pkg regexp/syntax, const InstAltMatch InstOp
pkg regexp/syntax, const InstCapture InstOp
pkg regexp/syntax, const InstEmptyWidth InstOp
pkg regexp/syntax, const InstFail InstOp

pkg regexp/syntax, const ErrUnexpectedParen = "unexpected )"
pkg regexp/syntax, const ErrUnexpectedParen ErrorCode
pkg regexp/syntax, const FoldCase = 1
pkg regexp/syntax, const InstAlt = 0
pkg regexp/syntax, const InstAltMatch = 1
pkg regexp/syntax, const InstCapture = 2
pkg regexp/syntax, const InstEmptyWidth = 3
pkg regexp/syntax, const InstFail = 5
pkg regexp/syntax, const InstMatch = 4