The _ _PAL_IMB intrinsic has the following declaration:
void __PAL_IMB(void);
This intrinsic function executes a CALL_PAL IMB (Instruction Memory Barrier) instruction, used to make the processor instruction stream coherent with system memory.
Use this instruction when writing self-modifying code. You must insert this instruction prior to executing code that has been modified; otherwise, the processor behavior is unpredictable.