Abstract: An apparatus has a data storage structure to store data items tagged by respective tag values and stores, in association with each data item, a respective tag group identifier to identify other data items having a same tag value within a collection of data items. The apparatus also has tag match circuitry to identify one or more hitting data items. Prioritisation circuitry is provided to select candidate data items which, relative to any other data items in the particular collection of data items having the same tag group identifier as the selected candidate data item is favoured according to an ordering of the data items. The prioritisation circuitry selects the one or more candidate data items before the identification of the hitting data items is available from the tag match circuitry. Data item selection circuitry selects a candidate data item for which the tag match circuitry detected a match.

Abstract: Instruction information generation circuitry generates instruction information. Instruction information storage circuitry comprises a plurality of elements having physical sub-elements configured to temporarily store units of instruction information. Allocation circuitry is configured to receive, from the instruction information generation circuitry, given instruction information. It determines a mapping of a plurality of ordered virtual sub-elements, such that each virtual sub-element maps onto a respective one of said physical sub-elements. The given instruction information is stored into the virtual sub-elements of a given element, according to the mapping, such that at least one virtual sub-element lower in said order has a higher priority than at least one virtual sub-element higher in said order. Sub-element deactivation circuitry is configured to track usage of said virtual sub-elements across the plurality of elements and adaptively deactivate virtual sub-elements.

Abstract: An apparatus has a data storage structure to store data items tagged by respective tag values and stores, in association with each data item, a respective tag group identifier to identify other data items having a same tag value within a collection of data items. The apparatus also has tag match circuitry to identify one or more hitting data items. Prioritisation circuitry is provided to select candidate data items which, relative to any other data items in the particular collection of data items having the same tag group identifier as the selected candidate data item is favoured according to an ordering of the data items. The prioritisation circuitry selects the one or more candidate data items before the identification of the hitting data items is available from the tag match circuitry. Data item selection circuitry selects a candidate data item for which the tag match circuitry detected a match.

Abstract: Processing circuitry performs processing operations in response to micro-operations. Front end circuitry supplies the micro-operations to be processed by the processing circuitry. Prediction circuitry generates a prediction of a number of loop iterations for which one or more micro-operations per loop iteration are to be supplied by the front end circuitry, where an actual number of loop iterations to be processed by the processing circuitry is resolvable by the processing circuitry based on at least one operand corresponding to a first loop iteration to be processed by the processing circuitry. The front end circuitry varies, based on a level of confidence in the prediction of the number of loop iterations, a supply rate with which the one or more micro-operations for at least a subset of the loop iterations are supplied to the processing circuitry.

Abstract: A data processing apparatus provides predictions for hard to predict instructions. Prediction circuitry generates predictions relating to predictable instructions in a stream and stores, with respect to each of the predictable instructions, a reference to a set of monitored instructions in the stream to be used for generating predictions for the predictable instructions. Processing circuitry executes the predictable instructions in the stream using the predictions. A given correlation parameter is stored between a given predictable instruction in the stream and a subset of the set of monitored instructions of the given predictable instruction to assist in generating the predictions. If the given correlation parameter is currently stored, the prediction circuitry generates a given prediction relating to the given predictable instruction based on the subset of the set of monitored instructions.

Abstract: A data processing apparatus is provided that includes bimodal control flow prediction circuitry for performing a prediction of whether a conditional control flow instruction will be taken. Storage circuitry stores, in association with the control flow instruction, a stored state of the data processing apparatus and reversal circuitry reverses the prediction in dependence on the stored state of the data processing apparatus corresponding with a current state of the data processing apparatus when execution of the control flow instruction is to be performed.

Abstract: Aspects of the present disclosure relate to an apparatus comprising prediction circuitry having a plurality of hierarchical prediction units to perform respective hierarchical predictions of instructions for execution, wherein predictions higher in the hierarchy have a higher expected accuracy than predictions lower in the hierarchy. Responsive to a given prediction higher in the hierarchy being different to a corresponding prediction lower in the hierarchy, the corresponding prediction lower in the hierarchy is corrected. A prediction correction metric determination unit determines a prediction correction metric indicative of an incidence of uncorrected predictions performed by the prediction circuitry. Fetch circuitry fetches instructions predicted by at least one of said plurality of hierarchical predictions, and delays said fetching based on the prediction correction metric indicating an incidence of uncorrected predictions below a threshold.

Abstract: Prediction circuitry predicts a number of iterations of a fetching process to be performed to control fetching of data/instructions for processing operations that are predicted to be performed by processing circuitry. The processing circuitry can tolerate performing unnecessary iterations of the fetching process following an over-prediction of the number of iterations. In response to the processing circuitry resolving an actual number of iterations, the prediction circuitry adjusts the prediction state information used to predict the number of iterations, based on whether a first predicted number of iterations, predicted based on a first iteration prediction parameter, provides a good prediction (when the first predicted number of iterations is in a range i_cnt to i_cnt+N, where i_cnt is the actual number of iterations and N?1), or a misprediction (when the first predicted number of iterations is outside the range i_cnt to i_cnt+N).

Abstract: Processing circuitry performs processing operations in response to micro-operations. Front end circuitry supplies the micro-operations to be processed by the processing circuitry. Prediction circuitry generates a prediction of a number of loop iterations for which one or more micro-operations per loop iteration are to be supplied by the front end circuitry, where an actual number of loop iterations to be processed by the processing circuitry is resolvable by the processing circuitry based on at least one operand corresponding to a first loop iteration to be processed by the processing circuitry. The front end circuitry varies, based on a level of confidence in the prediction of the number of loop iterations, a supply rate with which the one or more micro-operations for at least a subset of the loop iterations are supplied to the processing circuitry.

Abstract: There is provided an apparatus, method and medium. The apparatus comprises processing circuitry to perform data processing in response to decoded instructions and prediction circuitry to generate a prediction of a number of iterations of a fetching process. The fetching process is used to control fetching of data or instructions to be used in processing operations that are predicted to be performed by the processing circuitry. The processing circuitry is configured to tolerate performing one or more unnecessary iterations of the fetching process following an over-prediction of the number of iterations and, for at least one prediction, to determine a class of a plurality of prediction classes, each of which corresponds to a range of numbers of iterations. The prediction circuitry is also arranged to signal a predetermined number of iterations associated with the class to the processing circuitry to trigger at least the predetermined number of iterations of the fetching process.

Abstract: Aspects of the present disclosure relate to an apparatus. Instruction information generation circuitry generates instruction information. Instruction information storage circuitry comprises a plurality of elements having physical sub-elements configured to temporarily store units of instruction information, Allocation circuitry is configured to receive, from the instruction information generation circuitry, given instruction information, It determines a mapping of a plurality of ordered virtual sub-elements, such that each virtual sub-element maps onto a respective one of said physical sub-elements. The given instruction information is stored into the virtual sub-elements of a given element, according to the mapping, such that at least one virtual sub-element lower in said order has a higher priority than at least one virtual sub-element higher in said order.

Abstract: A data processing apparatus is provided that includes bimodal control flow prediction circuitry for performing a prediction of whether a conditional control flow instruction will be taken. Storage circuitry stores, in association with the control flow instruction, a stored state of the data processing apparatus and reversal circuitry reverses the prediction in dependence on the stored state of the data processing apparatus corresponding with a current state of the data processing apparatus when execution of the control flow instruction is to be performed.

Abstract: An apparatus has a fetch queue to identify a sequence of instructions to be fetched for execution and prediction circuitry to predict upcoming control flow and to control which instructions are identified in the fetch queue in dependence on the prediction. The prediction circuitry predicts multi-taken sequences which are sequences of instructions in which control flow is diverted by a first control flow changing instruction to a series of instructions terminating in a second control flow changing instruction that diverts control flow to a target address. The apparatus also has prediction confidence calculation circuitry to calculate confidence levels for respective multi-taken sequences. Each confidence level is indicative of a confidence in an accuracy of prediction of its respective multi-taken sequence.

Abstract: There is provided a data processing apparatus and method. The data processing apparatus comprises a filter circuit comprising storage circuitry to store program counter values and to assert a trigger signal in response to a lookup operation using a current program counter value hitting in the storage circuitry. The processing apparatus comprises a processing unit to generate an output in response to the trigger signal. The processing apparatus is provided with resolution circuitry, associated with a downstream processing stage, to determine whether the output is of use, and in that event to assert a false miss indication in the absence of the processing unit having been triggered to produce the output. The filter circuit is configured to maintain a trigger sensitivity metric in dependence on the false miss indication, and the chosen number of bits employed when performing the lookup operation is dependent on the trigger sensitivity metric.

Abstract: Aspects of the present disclosure relate to an apparatus comprising prediction circuitry having a plurality of hierarchical prediction units to perform respective hierarchical predictions of instructions for execution, wherein predictions higher in the hierarchy have a higher expected accuracy than predictions lower in the hierarchy. Responsive to a given prediction higher in the hierarchy being different to a corresponding prediction lower in the hierarchy, the corresponding prediction lower in the hierarchy is corrected. A prediction correction metric determination unit determines a prediction correction metric indicative of an incidence of uncorrected predictions performed by the prediction circuitry. Fetch circuitry fetches instructions predicted by at least one of said plurality of hierarchical predictions, and delays said fetching based on the prediction correction metric indicating an incidence of uncorrected predictions below a threshold.

Abstract: Circuitry comprises prediction storage to store, for a given branch operation, a multi-bit data item and indicator data defining a subset of bits of the multi-bit data item, the subset being one of an ordered succession of different subsets of bits of the multi-bit data item; and prediction generator circuitry to generate a predicted branch outcome for the given branch operation in dependence upon the subset of bits defined by the indicator data and, in response to generation of the predicted branch outcome, to change the subset of bits defined by the indicator data to a next subset in the ordered succession of subsets.

Abstract: Circuitry comprises prediction storage to store, for a given branch operation, a multi-bit data item and indicator data defining a subset of bits of the multi-bit data item, the subset being one of an ordered succession of different subsets of bits of the multi-bit data item; and prediction generator circuitry to generate a predicted branch outcome for the given branch operation in dependence upon the subset of bits defined by the indicator data and, in response to generation of the predicted branch outcome, to change the subset of bits defined by the indicator data to a next subset in the ordered succession of subsets.

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: An apparatus and method are provided for handling incorrect branch direction predictions. The apparatus has processing circuitry for executing instructions, branch prediction circuitry for making branch direction predictions in respect of branch instructions, and fetch circuitry for fetching instructions from an instruction cache in dependence on the branch direction predictions and for forwarding the fetched instructions to the processing circuitry for execution. A cache location buffer stores cache location information for a given branch instruction for which accuracy of the branch direction predictions made by the branch prediction circuitry is below a determined threshold. The cache location information identifies where within the instruction cache one or more instructions are stored that will need to be executed in the event that a subsequent branch direction prediction made for the given branch instruction is incorrect.

Abstract: A data processing apparatus is provided, which is able to provide predictions for hard to predict instructions. Prediction circuitry generates predictions relating to predictable instructions in a stream, where the prediction circuitry comprises storage circuitry to store, in respect of each of the predictable instructions, a reference to a set of monitored instructions in the stream to be used for generating predictions for the predictable instructions. Processing circuitry receives the predictions from the prediction circuitry and executes the predictable instructions in the stream using the predictions. Programmable instruction correlation parameter storage circuitry stores a given correlation parameter between a given predictable instruction in the stream and a subset of the set of monitored instructions of the given predictable instruction, to assist the prediction circuitry in generating the predictions.