GPIO pin not changing

At the beginning of an ISR, I am writing the below code:

GpioctrlRegs.GPAMUX1.bit.GPIO6=0 // as a GPIO

GpioDataRegs.GPASET.bit.GPIO6=1 // to make pin high

GpioctrlRegs.GPADIR1.bit.GPIO6=0 // GPIO6 as output

At the end of ISR, 

GpioDataRegs.GPACLEAR.bit.GPIO6=1 // to make pin low

But the pin is remaining continuously at 0.