// (x >> sc) & ac
(ANDconst [ac] (SRLconst [sc] x)) && isARM64BFMask(sc, ac, 0)
	=> (UBFX [armBFAuxInt(sc, arm64BFWidth(ac, 0))] x)
// (x & ac) >> sc
(SRLconst [sc] (ANDconst [ac] x)) && isARM64BFMask(sc, ac, sc)
	=> (UBFX [armBFAuxInt(sc, arm64BFWidth(ac, sc))] x)
// merge ANDconst and ubfx into ubfx
(ANDconst [c] (UBFX [bfc] x)) && isARM64BFMask(0, c, 0) =>

		return true
	}
	// match: (ANDconst [ac] (SLLconst [sc] x))
	// cond: isARM64BFMask(sc, ac, sc)
	// result: (UBFIZ [armBFAuxInt(sc, arm64BFWidth(ac, sc))] x)
	for {
		ac := auxIntToInt64(v.AuxInt)
		if v_0.Op != OpARM64SLLconst {
			break
		}
		sc := auxIntToInt64(v_0.AuxInt)
		x := v_0.Args[0]
		if !(isARM64BFMask(sc, ac, sc)) {
			break
		}
		v.reset(OpARM64UBFIZ)

func (bfc arm64BitField) getARM64BFwidth() int64 {
	return int64(bfc) & 0xff
}

// checks if mask >> rshift applied at lsb is a valid arm64 bitfield op mask.
func isARM64BFMask(lsb, mask, rshift int64) bool {
	shiftedMask := int64(uint64(mask) >> uint64(rshift))
	return shiftedMask != 0 && isPowerOfTwo64(shiftedMask+1) && nto(shiftedMask)+lsb < 64
}