At the MCS51 port the shown examples in "3.12.2 Naked Functions" are not
correct since SDCC 2.5.x
It's now already optimized (nearly) to the code of the "naked" one.
As in RFE 1156868 of 2005-03-04 (still open), I posted some additional code
for removing unneeded pushing, setting and popping the PSW if no registers
are used. If an other function is called within the ISR the removement will
*not* take place since the registers are marked as "used".