Technique for predicting behaviour of control flow instructions

Abstract

An apparatus has pointer storage to store pointer values for a plurality of pointers and increment circuitry, responsive to a series of increment events, to differentially increment the pointer values of the pointers. Training circuitry comprises tracker circuitry to maintain a plurality of tracker entries and cache circuitry to maintain a plurality of cache entries. Each tracker entry identifies a control flow instruction, and each cache entry stores a resolved behaviour of an instance of a control flow instruction identified by a tracker entry. For a given control flow instruction identified in a given tracker entry, the training circuitry performs a training process to seek to determine, as an associated pointer for the given control flow instruction, a pointer from amongst the plurality of pointers whose pointer value increments in a manner that meets a correlation threshold with occurrence of instances of the given control flow instruction. Promotion circuitry, responsive to detection of the correlation threshold being met for the given control flow instruction, allocates a prediction entry within prediction circuitry to identify the given control flow instruction and the associated pointer, and a behaviour record is established within the prediction entry identifying the resolved behaviour for one or more instances of the given control flow instruction. The behaviour record is arranged such that each resolved behaviour is associated with the pointer value of the associated pointer at the time that resolved behaviour was observed. Responsive to a prediction trigger associated with a replay of a given instance of the given control flow instruction, the prediction circuitry determines, in dependence on a current pointer value of the associated pointer, a predicted behaviour of the given instance of the given control flow instruction from the behaviour record within the prediction entry.