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    • 2. 发明申请
    • BRANCH TARGET ADDRESS CACHE USING HASHED FETCH ADDRESSES
    • 分支目标地址使用HASHED地址寻址
    • US20140122846A1
    • 2014-05-01
    • US13664659
    • 2012-10-31
    • ARM LIMITED
    • Vladimir VASEKINAllan John SKILLMANChiloda Ashan Senerath PATHIRANEJean-Baptiste BRELOT
    • G06F9/38
    • G06F9/3806
    • An integrated circuit 2 incorporates prefetch circuitry 12 for prefetching program instructions from a memory 6. The prefetch circuitry 12 includes a branch target address cache 28. The branch target address cache 28 stores data indicative of branch target addresses of previously encountered branch instructions fetched from the memory 6. For each previously encountered branch instructions, the branch target address cache stores a tag value indicative of a fetch address of that previously encountered branch instruction. The tag values stored are generated by tag value generating circuitry 32 which performs a hashing function upon a portion of the fetch address such that the tag value has a bit length less than the bit length of the portion of the fetch address concerned.
    • 集成电路2包含用于从存储器6预取程序指令的预取电路12.预取电路12包括分支目标地址高速缓存28.分支目标地址高速缓存28存储指示从先前遇到的分支指令的分支目标地址 对于每个先前遇到的分支指令,分支目标地址高速缓存存储指示先前遇到的分支指令的获取地址的标签值。 存储的标签值由标签值生成电路32产生,标签值生成电路32对获取地址的一部分执行散列函数,使得标签值的位长度小于相关提取地址的位长度。
    • 3. 发明申请
    • APPRATUS AND METHOD FOR USING PREDICTED RESULT VALUES
    • US20200004551A1
    • 2020-01-02
    • US16025116
    • 2018-07-02
    • Arm Limited
    • Vladimir VASEKINDavid Michael BULLAlexei FEDOROV
    • G06F9/38
    • An apparatus and method are provided for using predicted result values. The apparatus has processing circuitry for executing a sequence of instructions, and value prediction storage that comprises a plurality of entries, where each entry is used to identify a predicted result value for an instruction allocated to that entry. Dispatch circuitry maintains a record of pending instructions awaiting execution by the processing circuitry, and selects pending instructions from the record for dispatch to the processing circuitry for execution. The dispatch circuitry is arranged to enable at least one pending instruction to be speculatively executed by the processing circuitry using as a source operand a predicted result value provided by the value prediction storage. Allocation circuitry is arranged to apply a default allocation policy to identify a first instruction to be allocated an entry in the value prediction storage. However, the allocation circuitry is further responsive to a trigger condition to identify a dependent instruction whose result value will be dependent on the result value produced by executing the first instruction, and to then allocate an entry in the value prediction storage to store a predicted result value for the identified dependent instruction. Such an approach can enable performance improvements to be achieved through the use of predicted result values even in situations where the prediction accuracy of the predicted result value for the first instruction proves not to be that high, by instead enabling a predicted result value for the dependent instruction to be used to allow speculative execution of further dependent instructions.
    • 5. 发明申请
    • APPARATUS AND METHOD FOR USING PREDICTED RESULT VALUES
    • US20200004547A1
    • 2020-01-02
    • US16021178
    • 2018-06-28
    • Arm Limited
    • Vladimir VASEKINDavid Michael BULLChiloda Ashan Senarath PATHIRANEAlexei FEDOROV
    • G06F9/38G06F9/30G06F9/54G06F21/64
    • An apparatus and method are provided for using predicted result values. The apparatus has a processing unit that comprises processing circuitry for executing a sequence of instructions, and value prediction circuitry for identifying a predicted result value for at least one instruction. A result producing structure is provided that is responsive to a request issued from the processing unit when the processing circuitry is executing a first instruction, to produce a result value for the first instruction and return that result value to the processing unit. While waiting for the result value from the result producing structure, the processing circuitry can be arranged to speculatively execute at least one dependent instruction using a predicted result value for the first instruction as obtained from the value prediction circuitry. The request issued from the processing unit includes a signature value indicative of the predicted result value, and the result producing structure references the signature value in order to detect whether a mispredict condition exists indicating that the predicted result value differs from the result value. The apparatus further provides a mispredict signal transmission path via which the result producing structure, when the mispredict condition is detected, can assert a mispredict signal for receipt by the processing unit prior to the result value being available to the processing unit. Such an approach can reduce the misprediction penalty associated with using a mispredicted result value.
    • 8. 发明申请
    • APPARATUS AND METHOD FOR PERFORMING BRANCH PREDICTION
    • US20210279063A1
    • 2021-09-09
    • US17158276
    • 2021-01-26
    • Arm Limited
    • Vladimir VASEKINDavid Michael BULLFrederic Claude Marie PIRYAlexei FEDOROV
    • G06F9/38
    • An apparatus has processing circuitry for executing instructions and fetch circuitry for fetching the instructions for execution. When a branch instruction is encountered by the fetch circuitry, it determines subsequent instructions to be fetched in dependence on an initial branch direction prediction for the branch instruction made by branch prediction circuitry. Value prediction circuitry is used to maintain a predicted result value for one or more instructions, and dispatch circuitry maintains a record of pending instructions that have been fetched by the fetch circuitry and are awaiting execution by the processing circuitry, and selects pending instructions from the record for dispatch to the processing circuitry. When a given instruction whose predicted result value is maintained by the value prediction circuitry has a dependent instruction whose outcome is dependent on a result value of the given instruction, the dispatch circuitry nay be arranged to enable speculative execution of that dependent instruction using the predicted result value of the given instruction. Analysis circuitry is arranged, when the dependent instruction is the branch instruction, to detect a mispredict condition when an additional branch direction prediction for the branch instruction determined using the predicted result value for the given instruction is considered more accurate that the initial branch direction prediction, and the additional branch direction prediction differs to the initial branch direction prediction. On detection of the mispredict condition, a control signal is issued to indicate that the branch instruction has been mispredicted.