Branch target buffer arrangement for instruction prefetching

A branch target buffer, BTB, to store at least one BTB entry corresponding to a respective branch in a control flow in a sequence of machine-readable instructions of a computer program, the BTB entry comprising:

• a tag field to compare with a program counter of a fetch address generator to determine if there is a match between the program counter and information regarding a branch instruction currently stored in the BTB;
• and
• at least one further field to store information characteristic of the branch instruction identified by the corresponding tag field, the at least one further field allowing a conditional branch to be distinguished from an unconditional branch instruction;
• wherein the BTB has a predetermined storage capacity and wherein unconditional branch instructions are preferentially allocated storage space in the BTB relative to conditional branch instructions.

A method of buffering branch instructions in a branch target buffer, BTB, of a data processing apparatus, the method comprising:

• comparing with a program counter of a fetch address generator with a tag field of a BTB entry to determine if there is a match between the program counter and information regarding a branch instruction currently stored in the BTB;
• and
• using at least one further field of the BTB entry to store information characteristic of the branch instruction identified by the corresponding tag field, the at least one further field allowing a conditional branch instruction to be distinguished from an unconditional branch instruction;
• and
• preferentially allocating storage space in the BTB to conditional branch instructions relative to allocating storage space to unconditional branch instructions.

Machine-readable instructions provided on a non-transitory medium, the instructions upon execution to cause at least one processor to:

• compare with a program counter of a fetch address generator, a tag field of a BTB entry to determine if there is a match between the program counter and information regarding a branch instruction currently stored in the BTB;
• use at least one further field of the BTB entry to store information characteristic of the branch instruction identified by the corresponding tag field, the at least one further field allowing a conditional branch to be distinguished from an unconditional branch instruction;
• and
• control allocation of a predetermined storage capacity of the BTB to preferentially allocate storage space to conditional branch instructions relative to allocating storage space to unconditional branch instructions.