Set indexing for first-level and second-level set-associative cache

An apparatus comprising:

• a first-level set-associative cache comprising a plurality of sets of cache entries;
• a second-level set-associative cache comprising a plurality of sets of cache entries, where a number of sets in the first-level set-associative cache is the same as a number of sets in the second-level set-associative cache;
• and
• indexing circuitry to generate, based on a lookup address, a set index identifying a selected set of cache entries in the first-level set-associative cache and/or a selected set of cache entries in the second-level set-associative cache to be looked up for information associated with the lookup address,
• wherein:
• the indexing circuitry is configured to generate the set index using an indexing scheme which maps the lookup address to the same set index for both the first-level set-associative cache and the second-level set-associative cache;
• and
• the apparatus comprises branch prediction circuitry to determine at least one of:
• a predicted branch instruction behaviour associated with the lookup address based on branch prediction information cached in a cache entry of the first-level set-associative cache or the second-level set-associative cache associated with the lookup address;
• and
• a predicted target address for a first taken branch instruction predicted to occur within a block of one or more instructions associated with the lookup address, based on branch target buffer information cached in a cache entry of the first-level set-associative cache or the second-level set-associative cache associated with the lookup address.

A method comprising:

• caching information in a first-level set-associative cache comprising a plurality of sets of cache entries;
• caching information in a second-level set-associative cache comprising a plurality of sets of cache entries, where a number of sets in the first-level set-associative cache is the same as a number of sets in the second-level set-associative cache;
• generating, based on a lookup address, a set index identifying a selected set of cache entries in the first-level set-associative cache and/or a selected set of cache entries in the second-level set-associative cache to be looked up for information associated with the lookup address, where the set index is generated using an indexing scheme which maps the lookup address to the same set index for both the first-level set-associative cache and the second-level set-associative cache;
• and
• determining a predicted behaviour associated with the lookup address based on information cached in a cache entry of the first-level set-associative cache or the second-level set-associative cache associated with the lookup address.