Container-based instruction set

A non-transitory storage medium storing a computer program comprising instructions which, when executed by a host data processing apparatus, control the host data processing apparatus to provide an instruction execution environment for execution of target program code, the computer program comprising:

• front end program logic configured to fetch and decode instructions of the target program code;
• and
• processing program logic configured to control the host data processing apparatus to perform data processing operations in response to the instructions fetched and decoded by the front end program logic;
• in which:
• in a container-based instruction set mode for processing instructions from a fixed-length instruction set for which each instruction of the fixed-length instruction set is encoded using the same number of functional bits representing functionality of the instruction, the front end program logic is configured to decode the instructions according to an encoding scheme in which each instruction is required to meet an architectural encoding constraint requiring that, for a given instruction processed in the container-based instruction set mode:
• the given instruction is one of a plurality of instructions encoded fully within a C-bit container, where C is a fixed power-of-2 integer;
• each instruction has W functional bits, where W is a fixed non-power-of-2 integer;
• and
• no valid instruction is allowed to cross a boundary between C-bit containers;
• and
• the front end program logic is configured to support a branch operation specifying as a branch target any one of the plurality of instructions encoded within a given C-bit container.

A method comprising:

• fetching and decoding instructions using front end circuitry;
• and
• in response to the instructions fetched and decoded by the front end circuitry, performing data processing operations using processing circuitry;
• in which:
• in a container-based instruction set mode for processing instructions from a fixed-length instruction set for which each instruction of the fixed-length instruction set is encoded using the same number of functional bits representing functionality of the instruction, the instructions are decoded according to an encoding scheme in which each instruction is required to meet an architectural encoding constraint requiring that, for a given instruction processed in the container-based instruction set mode:
• the given instruction is one of a plurality of instructions encoded fully within a C-bit container, where C is a fixed power-of-2 integer;
• each instruction has W functional bits, where W is a fixed non-power-of-2 integer;
• and
• no valid instruction is allowed to cross a boundary between C-bit containers;
• and
• the front end circuitry is configured to support a branch operation specifying as a branch target any one of the plurality of instructions encoded within a given C-bit container.