I have originalyy posted this question to stackoverflow
IPP <= 7.1 has special in-place functions.
In IPP 8 they are deprecated: deprecation-summary
It is not clear if the new out-of-place functions also support in-place operation.
My guess is that for some of the functions it is OK to pass the same pointers for src/dst, but for others it is not, but this is not documented.
Here is the documentation