case arg_immediate_optional_0_65535_imm16:
		imm16 := (x >> 5) & (1<<16 - 1)
		return Imm_dcps(imm16)

	case arg_immediate_OptLSL_amount_16_0_16:
		imm16 := (x >> 5) & (1<<16 - 1)
		hw := (x >> 21) & (1<<2 - 1)
		shift := hw * 16
		if shift > 16 {
			return nil
		}
		return ImmShift{uint16(imm16), uint8(shift)}

	case arg_immediate_OptLSL_amount_16_0_48:
		imm16 := (x >> 5) & (1<<16 - 1)

	if p.Spadj == 0 && ins.as == AADDI && ins.imm >= -(1<<12) && ins.imm < 1<<12-1 {
		imm0 := ins.imm / 2
		imm1 := ins.imm - imm0

		// ADDI $(imm/2), REG, TO
		// ADDI $(imm-imm/2), TO, TO
		ins.imm = imm0
		insADDI := &instruction{as: AADDI, rd: ins.rd, rs1: ins.rd, imm: imm1}
		return []*instruction{ins, insADDI}
	}

	// LUI $high, TMP
	// ADDIW $low, TMP, TMP
	// <op> TMP, REG, TO

	y += x
	return (y-1)&y == 0
}

// isARM64addcon reports whether x can be encoded as the immediate value in an ADD or SUB instruction.
func isARM64addcon(v int64) bool {
	/* uimm12 or uimm24? */
	if v < 0 {
		return false
	}
	if (v & 0xFFF) == 0 {
		v >>= 12
	}
	return v <= 0xFFF
}

// setPos sets the position of v to pos, then returns true.