(Trunc32to8  (SignExt8to32  x)) => x
(Trunc32to16 (SignExt8to32  x)) => (SignExt8to16  x)
(Trunc32to16 (SignExt16to32 x)) => x
(Trunc64to8  (SignExt8to64  x)) => x
(Trunc64to16 (SignExt8to64  x)) => (SignExt8to16  x)
(Trunc64to16 (SignExt16to64 x)) => x
(Trunc64to32 (SignExt8to64  x)) => (SignExt8to32  x)
(Trunc64to32 (SignExt16to64 x)) => (SignExt16to32 x)
(Trunc64to32 (SignExt32to64 x)) => x

(Rsh8x64 x y) && !shiftIsBounded(v)        => (SRA (SignExt8to64 x) (CSEL [OpARM64LessThanU] <y.Type> y (Const64 <y.Type> [63]) (CMPconst [64] y)))
(Rsh8x(32|16|8) x y) && !shiftIsBounded(v) => (SRA (SignExt8to64 x) (CSEL [OpARM64LessThanU] <y.Type> y (Const64 <y.Type> [63]) (CMPconst [64] ((ZeroExt32to64|ZeroExt16to64|ZeroExt8to64) y))))

// constants

	// Conversions: signed extensions, zero (unsigned) extensions, truncations
	{name: "SignExt8to16", argLength: 1, typ: "Int16"},
	{name: "SignExt8to32", argLength: 1, typ: "Int32"},
	{name: "SignExt8to64", argLength: 1, typ: "Int64"},
	{name: "SignExt16to32", argLength: 1, typ: "Int32"},
	{name: "SignExt16to64", argLength: 1, typ: "Int64"},
	{name: "SignExt32to64", argLength: 1, typ: "Int64"},

	v_1 := v.Args[1]
	v_0 := v.Args[0]
	b := v.Block
	typ := &b.Func.Config.Types
	// match: (Rsh8x16 <t> x y)
	// cond: shiftIsBounded(v)
	// result: (SRA <t> (SignExt8to64 x) y)
	for {
		t := v.Type
		x := v_0
		y := v_1
		if !(shiftIsBounded(v)) {
			break
		}
		v.reset(OpARM64SRA)
		v.Type = t

// Lowering extension
// Note: we always extend to 64 bits even though some ops don't need that many result bits.
(SignExt8to16  ...) => (MOVBQSX ...)
(SignExt8to32  ...) => (MOVBQSX ...)
(SignExt8to64  ...) => (MOVBQSX ...)
(SignExt16to32 ...) => (MOVWQSX ...)
(SignExt16to64 ...) => (MOVWQSX ...)
(SignExt32to64 ...) => (MOVLQSX ...)

(ZeroExt8to16  ...) => (MOVBQZX ...)
(ZeroExt8to32  ...) => (MOVBQZX ...)

	v_0 := v.Args[0]
	// match: (SignExt8to64 (Const8 [c]))
	// result: (Const64 [int64(c)])
	for {
		if v_0.Op != OpConst8 {
			break
		}
		c := auxIntToInt8(v_0.AuxInt)
		v.reset(OpConst64)
		v.AuxInt = int64ToAuxInt(int64(c))
		return true
	}
	// match: (SignExt8to64 (Trunc64to8 x:(Rsh64x64 _ (Const64 [s]))))
	// cond: s >= 56
	// result: x

	},
	{
		name:    "SignExt8to16",
		argLen:  1,
		generic: true,
	},
	{
		name:    "SignExt8to32",
		argLen:  1,
		generic: true,
	},
	{
		name:    "SignExt8to64",
		argLen:  1,
		generic: true,
	},
	{
		name:    "SignExt16to32",
		argLen:  1,
		generic: true,
	},
	{
		name:    "SignExt16to64",
		argLen:  1,