in the "interrupt" function,call a "c" function,press "F8" ,but the "c" function didn't execute sometimes,in other words,it executed "nop" operation,why?

i got.
the reasion:
"Our PRO compilers with OCG (of which the HOLTEK compiler is one) do very aggressive dead-code elimination and if a C function or variable is not accessed from within C code it will probably not exist in the output."