GREG Expression
Description:
Allocates a new global register. The expression is evaluated and is used to initialize the global register before the program starts. If the value is not zero, mmixal assumes that the value is constant and can be used in address calculations.
Register $255 is always a global register. The first GREG will allocate $254 and the next $253, and so on.
An optional label can be used to give a name to the new global register.