A branch predictor of a processor includes one or more prediction structures, including a predicted branch address and predicted branch direction, that identify predicted branches. To reduce power consumption, the branch predictor selects one or more of the prediction structures that are not expected to provide useful branch prediction information and filters the selected structures such that the filtered structures are not used for branch prediction. The branch predictor thereby reduces the amount of power used for branch prediction without substantially reducing the accuracy of the predicted branches.

A system, processor, programming product and/or method including: an instruction dispatch unit configured to dispatch instructions of a compare immediate-conditional branch instruction sequence; and a compare register having at least one entry to hold information in a plurality of fields. Operations include: writing information from a first instruction of the compare immediate-conditional branch instruction sequence into one or more of the plurality of fields in an entry in the compare register; writing an immediate field and the ITAG of a compare immediate instruction into the entry in the compare register; writing, in response to dispatching a conditional branch instruction, an inferred compare result value into the entry in the compare register; comparing a computed compare result value to the inferred compare result value stored in the entry in the compare register; and not execute the compare immediate instruction or the conditional branch instruction.

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. 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.

A predicated-loop-terminating branch instruction controls, based on whether a loop termination condition is satisfied, whether the processing circuitry should process a further iteration of a predicated loop body or process a following instruction. If at least one unnecessary iteration of the predicated loop body is processed following a mispredicted-non-termination branch misprediction when the loop termination condition is mispredicted as unsatisfied for a given iteration when it should have been satisfied, processing of the at least one unnecessary iteration of the predicated loop body is predicated to suppress an effect of the at least one unnecessary iteration. When the mispredicted-non-termination branch misprediction is detected for the given iteration of the predicated-loop-terminating branch instruction, in response to determining that a flush suppressing condition is satisfied, flushing of the at least one unnecessary iteration of the predicated loop body is suppressed as a response to the mispredicted-non-termination branch misprediction.

Methods and systems for determining a priority of a threads is described. A processor can execute branch instructions of the thread. The processor can predict branch instruction outcomes of the branch instructions of the thread. The processor can increment a misprediction count of the thread in response to an actual execution of a branch instruction of the thread being different from a corresponding branch instruction prediction outcome of the thread. The processor can determine the priority of the thread based on the misprediction count of the thread.

A branch target buffer, BTB, is provided 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 has a tag field to compare with a program counter of a fetch address generator and at least one further field to store information characteristic of the branch instruction identified by the corresponding tag field and allowing a conditional branch to be distinguished from an unconditional branch instruction. The BTB has a predetermined storage capacity and is utilized such that unconditional branch instructions are preferentially allocated storage space in the BTB relative to conditional branch instructions.

The present disclosure is directed to systems and methods for mitigating or eliminating the effectiveness of a side-channel based attack, such as one or more classes of an attack commonly known as Spectre. Novel instruction prefixes, and in certain embodiments one or more corresponding instruction prefix parameters, may be provided to enforce a serialized order of execution for particular instructions without serializing an entire instruction flow, thereby improving performance and mitigation reliability over existing solutions. In addition, improved mitigation of such attacks is provided by randomizing both the execution branch history as well as the source address of each vulnerable indirect branch, thereby eliminating the conditions required for such attacks.

An embodiment of an integrated circuit may comprise a return stack buffer (RSB), a speculative return stack buffer (SRSB), and circuitry coupled to the RSB and the SRSB, the circuitry to track a count until the SRSB is empty at a time of a prediction by a branch prediction unit, and return an output from the branch prediction unit that corresponds to one of the RSB and the SRSB based at least in part on the count until the SRSB is empty. Other embodiments are disclosed and claimed.

An electronic device is described that handles control transfer instructions (CTIs) when executing instructions in program code. The electronic device has a processor that includes a branch prediction functional block and a sequential fetch logic functional block. The sequential fetch logic functional block determines, based on a record associated with a CTI, that a specified number of fetch groups of instructions that were previously determined to include no CTIs are to be fetched for execution in sequence following the CTI. When each of the specified number of fetch groups is fetched and prepared for execution, the sequential fetch logic prevents corresponding accesses of the branch prediction functional block for acquiring branch prediction information for instructions in that fetch group.

Methods and apparatus relating to loop driven region based frontend translation control for performant and secure data-space guided micro-sequencing are described. In an embodiment, Data-space Translation Logic (DTL) circuitry receives a static input and a dynamic input and generates one or more outputs based at least in part on the static input and the dynamic input. A frontend counter generates a count value for the dynamic input based at least in part on an incremented/decremented counter value and a next counter value from the DTL circuitry. The DTL circuitry is capable to receive a new dynamic input prior to consumption of the one or more outputs. Other embodiments are also disclosed and claimed.