How to define a blackbox data type in gcc?

[Bingfeng Mei]

Hello,
I am wondering how to define a blackbox data type in gcc.  It can be too
wide and irregular to be represented by current data types. It needs to
be assigned to special register files.  I don't care and don't want to
touch its content except using intrinsics (builtin) functions.  An
example of such data type is to represent value in a MAC register.  Is
there are convenient way to do that? Thanks in advance,
 
Cheers,
Bingfeng Mei
 
Broadcom UK