#define __disable_interrupt() __bic_SR_register(0x80)
__disable_interrupt disables global interrupts by clearing the I bit in the status register and returns the value of the status register before the I bit is cleared. You can restore the state of the I bit from the value returned from __disable_interrupt by using the __restore_interrupt intrinsic function.
__disable_interrupt is an intrinsic function and produces inline code.