MOVL	b_base+0(FP), SI
	MOVL	b_len+4(FP), CX
	MOVB	c+12(FP), AL
	MOVL	SI, DI
	CLD; REPN; SCASB
	JZ 3(PC)
	MOVL	$-1, ret+16(FP)
	RET
	SUBL	SI, DI
	SUBL	$1, DI
	MOVL	DI, ret+16(FP)
	RET

TEXT ·IndexByteString(SB),NOSPLIT,$0-16
	MOVL	s_base+0(FP), SI
	MOVL	s_len+4(FP), CX
	MOVB	c+8(FP), AL
	MOVL	SI, DI
	CLD; REPN; SCASB
	JZ 3(PC)
	MOVL	$-1, ret+12(FP)
	RET
	SUBL	SI, DI
	SUBL	$1, DI

	}

	switch inst.Op {
	case INSB, INSD, INSW, OUTSB, OUTSD, OUTSW, MONITOR, MWAIT, XLATB:
		iargs = nil

	case STOSB, STOSW, STOSD, STOSQ:
		iargs = iargs[:1]

	case LODSB, LODSW, LODSD, LODSQ, SCASB, SCASW, SCASD, SCASQ:
		iargs = iargs[1:]
	}

	const (
		haveData16 = 1 << iota
		haveData32
		haveAddr16
		haveAddr32
		haveXacquire
		haveXrelease
		haveLock
		haveHintTaken

		case ES:
			haveES = true
		case FS:
			haveFS = true
		case GS:
			haveGS = true
		case SS:
			haveSS = true
		}
		switch inst.Op {
		case INSB, INSW, INSD, STOSB, STOSW, STOSD, STOSQ, SCASB, SCASW, SCASD, SCASQ:
			// These do not accept segment prefixes, at least in the GNU rendering.
		default:
			if *usedPrefixes {
				break
			}
			for i := len(inst.Prefix) - 1; i >= 0; i-- {

	"RSQRTSS",
	"SAHF",
	"SALB",
	"SALL",
	"SALQ",
	"SALW",
	"SARB",
	"SARL",
	"SARQ",
	"SARW",
	"SARXL",
	"SARXQ",
	"SBBB",
	"SBBL",
	"SBBQ",
	"SBBW",
	"SCASB",
	"SCASL",
	"SCASQ",
	"SCASW",
	"SETCC",
	"SETCS",
	"SETEQ",
	"SETGE",
	"SETGT",
	"SETHI",
	"SETLE",
	"SETLS",
	"SETLT",
	"SETMI",
	"SETNE",
	"SETOC",
	"SETOS",

		case STOSD:
			inst.Args[1] = EAX
		case STOSQ:
			inst.Args[1] = RAX
		}
		usedAddrSize = true

	case SCASB, SCASW, SCASD, SCASQ:
		inst.Args[1] = Mem{Segment: ES, Base: baseRegForBits(addrMode) + DI - AX}
		switch inst.Op {
		case SCASB:
			inst.Args[0] = AL
		case SCASW:
			inst.Args[0] = AX
		case SCASD:
			inst.Args[0] = EAX
		case SCASQ:
			inst.Args[0] = RAX

	ROUNDSS:         "ROUNDSS",
	RSM:             "RSM",
	RSQRTPS:         "RSQRTPS",
	RSQRTSS:         "RSQRTSS",
	SAHF:            "SAHF",
	SAR:             "SAR",
	SBB:             "SBB",
	SCASB:           "SCASB",
	SCASD:           "SCASD",
	SCASQ:           "SCASQ",
	SCASW:           "SCASW",
	SETA:            "SETA",
	SETAE:           "SETAE",
	SETB:            "SETB",
	SETBE:           "SETBE",

	SBBB (BX), DL                           // 1a13
	SBBB (R11), DL                          // 411a13
	SBBB (BX), R11                          // 441a1b
	SBBB (R11), R11                         // 451a1b
	SCASB                                   // ae
	SCASL                                   // af
	SCASQ                                   // 48af
	SCASW                                   // 66af