There is provided a data processing apparatus comprising decode circuitry responsive to receipt of a block of instructions to generate control signals indicative of each of the block of instructions, and to analyse the block of instructions to detect a potential hazard instruction. The data processing apparatus is provided with decode circuitry to encode information indicative of a clean restart point into the control signals associated with the potential hazard instruction. The data processing apparatus is provided with data processing circuitry to perform out-of-order execution of at least some of the block of instructions, and control circuitry responsive to a determination, at execution of the potential hazard instruction, that data values used as operands for the potential hazard instruction have been modified by out-of-order execution of a subsequent instruction, to restart execution from the clean restart point and to flush held data values from the data processing circuitry.

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.

Embodiments of systems, methods, and apparatuses for heterogeneous computing are described. In some embodiments, a hardware heterogeneous scheduler dispatches instructions for execution on one or more plurality of heterogeneous processing elements, the instructions corresponding to a code fragment to be processed by the one or more of the plurality of heterogeneous processing elements, wherein the instructions are native instructions to at least one of the one or more of the plurality of heterogeneous processing elements.

A computer-implemented method for of constrained carries on speculative counters includes providing one or more speculative counters having an upper portion of most significant bits partially embedded in a random-access memory (RAM) array, and a pre-counter portion external to the RAM array having a plurality of least significant bits. The one or more speculative counters are configured to count a plurality of events of interest during a processor core instruction execution. A carry output from the pre-counter portion to the RAM array is suppressed for a duration of a speculative event period.

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.

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 apparatus comprises processing circuitry 14 to perform data processing in response to instructions, the processing circuitry supporting speculative processing of read operations for reading data from a memory system 20, 22; and control circuitry 12, 14, 20 to identify whether a sequence of instructions to be processed by the processing circuitry includes a speculative side-channel hint instruction indicative of whether there is a risk of information leakage if at least one subsequent read operation is processed speculatively, and to determine whether to trigger a speculative side-channel mitigation measure depending on whether the instructions include the speculative side-channel hint instruction. This can help to reduce the performance impact of measures taken to protect against speculative side-channel attacks.

A computer-implemented method of performing a link stack based prefetch augmentation using a sequential prefetching includes observing a call instruction in a program being executed, and pushing a return address onto a link stack for processing the next instruction. A stream of instructions is prefetched starting from a cached line address of the next instruction and is stored in an instruction cache.

A computer system, processor, programming instructions and/or method of processing data that includes a main register file having a plurality of entries for storing data; an accumulator register file having a plurality of entries for storing data wherein multiple main register file entries are mapped to one accumulator register file entry in the at least one accumulator register file; a logical register mapper to track and map logical registers to main register file entries, and a history buffer. Processing wide data width instructions includes evicting and restoring information from a single primary entry in the logical register mapper through a single read or write port in the logical register mapper without evicting or restoring the remaining other multiple main register file entries mapped in the accumulator register.

A method of verifying authenticity of a speculative load instruction is disclosed which includes receiving a new speculative source-destination pair (PAIR), wherein the source represents a speculative load instruction and the destination represents an associated destination virtual memory location holding data to be loaded onto a register with execution of the source, checking the PAIR against one or more memory tables associated with non-speculative source-destination pairs, if the PAIR exists in the one or more memory tables, then executing the instruction associated with the source of the PAIR, if the PAIR does not exist, then i) waiting until the speculation of the source instruction has cleared as being non-speculative, ii) updating the one or more memory tables, and iii) executing the instruction associated with the source, and if the speculation of the source instruction of the PAIR does not clear as non-speculative, then the source is nullified.