Question about interrupts

Hello all, 

When interrupts are handled through interrupt gate cpu automatically clears IF 
flag. 

but to allow nesting kernel sets the IF flag in handle_irq_event - for 2.6.11

but in 2.6.39 how the interrupts are re-enabled so as to facilitate nesting of 
interrupts
I am unable to find local_irq_enable in do_IRQ()

Thanks in advance.