Returning a default value when reading from an architected register, which has been deactivated in response to a last use indication

摘要

A processor has a pool of physical registers, which are mapped to the logical registers of the instruction set architecture. When an instruction contains an indication of the last use of a value in an architected register, the architected register is deactivated and the association between a physical register and that architected register is removed. When an instruction attempts to read from an architected register, it checks to see if the register is deactivated. If so, a default value is returned. Otherwise, the value in the associated physical register is returned. When an instruction attempts to write to an architected register and the architected register is not deactivated, the value is written to the physical register associated with it. If the architected register has been deactivated, it is activated and a new physical register is associated with it. The value is then written to the physical register.