The PIC16 port emits code which is incompatible with the extended instruction set available with many newer devices. Make sure to always explicitly disable it, usually using
static __code char __at(__CONFIG4L) conf4l = /* more flags & */ _XINST_OFF_4L;
Some devices (namely 18f2455, 18f2550, 18f4455, and 18f4550) use _ENHCPU_OFF_4L instead of _XINST_OFF_4L.
The PIC16 port currently passes most but not all of the tests in SDCC's regression test suite (see section 7.9), thus no automatic regression tests are currently performed for the PIC16 target.