readonly register

[BELBACHIR Selim]

Hi,

I'm trying to support an 'in' instruction which reads a value on a peripheral and writes it into a $INP register.
The $INP register can be used in almost every insn as input operand (add, sub, mul ...).
I defined a builting to access the 'in' instruction.

How should I express to gcc that the $INP register can only be 'read' and must never be written?

For the moment, I encounter a problem during IRA pass where some of my 'classic' registers are reloaded into $INP (apparently because I have no register left).

Regards,

  Selim