IRET
This instruction returns from an interrupt routine.
First, it pops the top of the stack (which should contain the return address provided by a CALL). Then, it jumps to the obtained address, i.e., copies the jump address into IP.
Next, it pops the stack again, but this time the top of the stack is the value of FLAGS. The obtained value is then copied into FLAGS. Thus, the flags are modified according to what is popped.
Note that, although this instruction modifies the flags, as it is returning from an interrupt routine, the flags should be the same as before the interrupt when returning to the original execution flow.
Additionally, this instruction does not enable interrupts per se. If interrupts were enabled before the interrupt, they will be re-enabled when copying FLAGS, but if they were not enabled, they will not be enabled. This is useful because, for example, it allows software interrupts to be executed within an interrupt routine without re-enabling interrupts.
Usage
IRETEncoding
00011011