Abstract: An apparatus and method are provided for processing instructions fetched from memory. Decode circuitry is used to decode the fetched instructions in order to produce decoded instructions, and downstream circuitry then processes the decoded instructions in order to perform the operations specified by those decoded instructions. Dispatch circuitry is arranged to dispatch to the downstream circuitry up to N decoded instructions per dispatch cycle, and is arranged to determine, based on a given candidate sequence of decoded instructions being considered for dispatch in a given dispatch cycle, whether at least one resource conflict within the downstream circuitry would occur in the event that the given candidate sequence of decoded instructions is dispatched in the given dispatch cycle.

Abstract: A data processing apparatus is provided. It includes control flow detection prediction circuitry that performs a presence prediction of whether a block of instructions contains a control flow instruction. A fetch queue stores, in association with prediction information, a queue of indications of the instructions and the prediction information comprises the presence prediction. An instruction cache stores fetched instructions that have been fetched according to the fetch queue. Post-fetch correction circuitry receives the fetched instructions prior to the fetched instructions being received by decode circuitry, the post-fetch correction circuitry includes analysis circuitry that causes the fetch queue to be at least partly flushed in dependence on a type of a given fetched instruction and the prediction information associated with the given fetched instruction.

Abstract: Aspects of the present disclosure relate an apparatus comprising fetch circuitry and instruction storage circuitry. The fetch circuitry is to fetch instructions for execution by execution circuitry. The instruction storage circuitry is to store temporary copies of fetched instructions. The fetch circuitry is configured to preferentially fetch instructions from the instruction storage circuitry. The instruction storage circuitry is configured to, responsive to a storage condition being met, begin storing copies of consecutive fetched instructions, the storage condition indicating a utility of a current fetched instruction; and to, responsive to determining that a number of said stored consecutive instructions has reached a storage threshold, cease storing copies of subsequent fetched instructions.

Abstract: An apparatus comprises first-level and second-level set-associative caches each comprising the same number of sets of cache entries. Indexing circuitry generates, based on a lookup address, a set index identifying which set of the first-level set-associative cache or the second-level set-associative cache is a selected set of cache entries to be looked up for information associated with the lookup address. The indexing circuitry generates 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. This can make migration of cached information between the cache levels more efficient, which can be particularly useful for caches with high access frequency, such as branch target buffers for a branch predictor.

Abstract: Data processing apparatuses and methods of processing data are disclosed. The operations comprise: storing copies of data items; and storing, in a producer pattern history table, a plurality of producer-consumer relationships, each defining an association between producer load indicator and a plurality of consumer load entries, each consumer load entry comprising a consumer load indicator and one or more usefulness metrics. Further steps comprise: initiating, in response to a data load from an address corresponding to the producer load indicator in the producer pattern history table and when at least one of the corresponding one or more usefulness meets a criterion, a producer prefetch of data to be prefetched for storing as a local copy; and issuing, when the data is returned, one or more consumer prefetches to return consumer data from a consumer address generated from the data returned by the producer prefetch and a consumer load indicator of a consumer load entry.

Abstract: There is provided a data processing apparatus and method for storing a plurality of prediction cache entries in a prediction cache with associativity greater than one comprising a plurality of prediction cache ways, each of the plurality of prediction entries defining an association between a prediction cache lookup address and target information; and storing a plurality of stream entries, each stream entry corresponding to a sequence of prediction cache lookup addresses and comprising: a stream identifier defined by two or more sequential prediction cache lookup addresses of the sequence, and a plurality of sequential way predictions, each way prediction of the plurality of sequential way predictions defining, for a given position in the sequence of prediction cache lookup addresses, a prediction cache way to be looked up in the prediction cache to identify a prediction entry associated with the prediction cache lookup address at the given position in the sequence.

Abstract: First and second-level caches are provided. Cache control circuitry performs a first-level cache lookup of the first-level cache based on a lookup address, to determine whether the first-level cache stores valid cached data corresponding to the lookup address. When lookup hint information associated with the lookup address is available, the cache control circuitry determines based on the lookup hint information whether to activate or deactivate a second-level cache lookup of the second-level cache. The lookup hint information is indicative of whether the second-level cache is predicted to store valid cached data associated with the lookup address. When the second-level cache lookup is activated, the second-level cache lookup of the second-level cache is performed based on the lookup address to determine whether the second-level cache stores valid cached data corresponding to the lookup address.

Abstract: An apparatus and method are provided for making predictions for instruction flow changing instructions. The apparatus has a fetch queue that identifies a sequence of instructions to be fetched for execution by execution circuitry, and prediction circuitry for making predictions in respect of instruction flow changing instructions, and for controlling which instructions are identified in the fetch queue in dependence on the predictions. The prediction circuitry has a target prediction storage used to identify target addresses for instruction flow changing instructions that are predicted as taken.

Abstract: In register renaming circuitry architectural registers specified in instructions are mapped to physical registers using a mapping table. Operations to be performed with respect to the physical registers are generated in dependence on the instructions and on the mapping table entries. When the mapping table has a mapping of a first instruction destination physical register for a first instruction destination architectural register specified in a first instruction, a second instruction specifying the first instruction destination architectural register as a second instruction source architectural register causes an adapted second operation to be generated corresponding to the second instruction using at least one first instruction source physical register as at least one second instruction source physical register. The adapted second operation incorporates a first operation corresponding to the first instruction.

Abstract: An apparatus has processing circuitry, and history storage circuitry to store local history records. Each local history record corresponds to a respective subset of instruction addresses and tracks a sequence of observed instruction behaviour observed for successive instances of instructions having addresses in that subset. Pointer storage circuitry to store a shared pointer shared between the local history records. The shared pointer indicates a common storage position reached in each local history record. Prediction circuitry determines predicted instruction behaviour for a given instruction address based on a selected portion of a selected local history record stored in the history storage circuitry. The prediction circuitry selects the selected local history record based on the given instruction address and selects the selected portion based on the shared pointer.

Abstract: A data processing apparatus is provided. It includes cache circuitry to store a plurality of items, each having an associated indicator. Processing circuitry executes instructions using at least some of the plurality of items. Fill circuitry inserts a new item into the cache circuitry. Eviction circuitry determines which of the plurality of items is to be a victim item based on the indicator, and evicts the victim item from the cache circuitry. Detection circuitry detects a state of the processing circuitry at a time that the new item is inserted into the cache circuitry, and sets the indicator in dependence on the state.

Abstract: Data processing apparatuses and methods of processing data are disclosed. The operations comprise: storing copies of data items; and storing, in a producer pattern history table, a plurality of producer-consumer relationships, each defining an association between producer load indicator and a plurality of consumer load entries, each consumer load entry comprising a consumer load indicator and one or more usefulness metrics. Further steps comprise: initiating, in response to a data load from an address corresponding to the producer load indicator in the producer pattern history table and when at least one of the corresponding one or more usefulness meets a criterion, a producer prefetch of data to be prefetched for storing as a local copy; and issuing, when the data is returned, one or more consumer prefetches to return consumer data from a consumer address generated from the data returned by the producer prefetch and a consumer load indicator of a consumer load entry.

Abstract: An apparatus comprises first-level and second-level set-associative caches each comprising the same number of sets of cache entries. Indexing circuitry generates, based on a lookup address, a set index identifying which set of the first-level set-associative cache or the second-level set-associative cache is a selected set of cache entries to be looked up for information associated with the lookup address. The indexing circuitry generates 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. This can make migration of cached information between the cache levels more efficient, which can be particularly useful for caches with high access frequency, such as branch target buffers for a branch predictor.

Abstract: An apparatus and method are provided for processing instructions fetched from memory. Decode circuitry is used to decode the fetched instructions in order to produce decoded instructions, and downstream circuitry then processes the decoded instructions in order to perform the operations specified by those decoded instructions. Dispatch circuitry is arranged to dispatch to the downstream circuitry up to N decoded instructions per dispatch cycle, and is arranged to determine, based on a given candidate sequence of decoded instructions being considered for dispatch in a given dispatch cycle, whether at least one resource conflict within the downstream circuitry would occur in the event that the given candidate sequence of decoded instructions is dispatched in the given dispatch cycle.

Abstract: First and second-level caches are provided. Cache control circuitry performs a first-level cache lookup of the first-level cache based on a lookup address, to determine whether the first-level cache stores valid cached data corresponding to the lookup address. When lookup hint information associated with the lookup address is available, the cache control circuitry determines based on the lookup hint information whether to activate or deactivate a second-level cache lookup of the second-level cache. The lookup hint information is indicative of whether the second-level cache is predicted to store valid cached data associated with the lookup address. When the second-level cache lookup is activated, the second-level cache lookup of the second-level cache is performed based on the lookup address to determine whether the second-level cache stores valid cached data corresponding to the lookup address.

Abstract: A data processing apparatus and a method are disclosed.

Abstract: An apparatus comprises a cache comprising cache entries, each cache entry storing cached information and an entry usefulness value indicative of usefulness of the cached information. Base usefulness storage circuitry stores a base usefulness value. Cache replacement control circuitry controls, based on a usefulness level determined for a given cache entry, whether the given cache entry is selected for replacement. The cache replacement control circuitry determines the usefulness level for the given cache entry based on a difference between the entry usefulness value specified by the given cache entry and the base usefulness value stored in the base usefulness storage circuitry.

Abstract: A data processing apparatus is provided. It includes processing circuitry for speculatively executing a plurality of instructions. Storage circuitry stores a current state of the processing circuitry and a plurality of previous states of the processing circuitry. Execution of the plurality of instructions changes the current state of the processing circuitry. Flush circuitry replaces, in response to a miss-prediction, the current state of the processing circuitry with a replacement one of the plurality of previous states of the processing circuitry.

Abstract: A data processing apparatus is provided, which includes a cache to store operations produced by decoding instructions fetched from memory. The cache is indexed by virtual addresses of the instructions in the memory. Receiving circuitry receives an incoming invalidation request that references a physical address in the memory. Invalidation circuitry invalidates entries in the cache where the virtual address corresponds with the physical address. Coherency is thereby achieved when using a cache that is indexed using virtual addresses.

Abstract: An apparatus is described, comprising processing circuitry to speculatively execute an earlier instruction and a later instruction by generating a prediction of an outcome of the earlier instruction and a prediction of an outcome of the later instruction, wherein the prediction of the outcome of the earlier instruction causes a first control flow path to be executed. The apparatus also comprises storage circuitry to store the outcome of the later instruction in response to the later instruction completing, and flush circuitry to generate a flush in response to the prediction of the outcome of the earlier instruction being incorrect. Permission circuitry permits the generating of the prediction by the processing circuitry.