// TODO: optimize these cases?
(Ctz32NonZero ...) => (Ctz32 ...)
(Ctz64NonZero ...) => (Ctz64 ...)

(Ctz64 x) && buildcfg.GOPPC64<=8 => (POPCNTD (ANDN <typ.Int64> (ADDconst <typ.Int64> [-1] x) x))
(Ctz64 x) => (CNTTZD x)
(Ctz32 x) && buildcfg.GOPPC64<=8 => (POPCNTW (MOVWZreg (ANDN <typ.Int> (ADDconst <typ.Int> [-1] x) x)))
(Ctz32 x) => (CNTTZW (MOVWZreg x))
(Ctz16 x) => (POPCNTW (MOVHZreg (ANDN <typ.Int16> (ADDconst <typ.Int16> [-1] x) x)))

		v1 := b.NewValue0(v.Pos, OpPPC64ADDconst, typ.Int64)
		v1.AuxInt = int64ToAuxInt(-1)
		v1.AddArg(x)
		v0.AddArg2(v1, x)
		v.AddArg(v0)
		return true
	}
	// match: (Ctz64 x)
	// result: (CNTTZD x)
	for {
		x := v_0
		v.reset(OpPPC64CNTTZD)
		v.AddArg(x)
		return true
	}
}
func rewriteValuePPC64_OpCtz8(v *Value) bool {
	v_0 := v.Args[0]
	b := v.Block