Apparatus and method for mapping architectural registers to physical registers

A method of operating an apparatus to map from architectural registers of a set of architectural registers to physical registers of a set of physical registers, said set of architectural registers being registers as specified by instructions of an instruction set and said set of physical registers being physical registers for use when executing said instructions on processing circuitry of the apparatus, the method comprising:

• (i) responsive to a current state of said apparatus, identifying which physical registers of said set of physical registers form a pool of physical registers available to be mapped to an architectural register specified by an instruction to be executed;
• (ii) for said instruction to be executed, performing a register renaming operation to map each architectural register specified by the instruction to one of said physical registers from said pool;
• (iii) storing configuration data whose value is modified during operation of the processing circuitry to identify a view of the set of architectural registers applicable to a current software execution level of the processing circuitry, such that when said configuration data has a first value, the configuration data identifies at least one architectural register of said set of architectural registers which is not present in said view of the set of architectural registers applicable to the current software execution level of the processing circuitry and does not require mapping to a physical register;
• and
• (iv) at said step (i), referencing said configuration data, such that when said configuration data has said first value, the number of physical registers in said pool is increased due to the reduction in the number of architectural registers which require mapping to physical registers.

Apparatus for processing data, comprising:

• a set of physical register means for storing data;
• processing means for executing instructions of an instruction set, the processing means requiring access to said data when executing said instructions;
• register renaming means for mapping from architectural register means of a set of architectural register means to physical register means of said set of physical register means, said set of architectural register means being register means as specified by said instructions and said set of physical register means being physical register means for use when executing said instructions;
• available register identifying means, responsive to a current state of said apparatus, for identifying which physical register means of said set of physical registers form a pool of physical register means available to be mapped by said register renaming means to an architectural register means specified by an instruction to be executed;
• and
• configuration storage means for storing configuration data whose value is modified during operation of the processing means to identify a view of the set of architectural register means applicable to a current software execution level of the processing means, such that when said configuration data has a first value, the configuration data identifies at least one architectural register means of said set of architectural register means which is not present in said view of the set of architectural register means applicable to the current software execution level of the processing means and does not require mapping to a physical register means by the register renaming means;
• the available register identifying means for referencing said configuration storage means, such that when said configuration data has said first value, the number of physical register means in said pool is increased due to the reduction in the number of architectural register means which require mapping to physical register means.