Abstract: A method utilizes information provided by performance monitoring hardware to dynamically adjust the number of levels of speculative branch predictions allowed (typically 3 or 4 per thread). for a processor core. The information includes cycles-per-instruction (CPI) for the processor core and number of memory accesses per unit time. If the CPI is below a CPI threshold; and the number of memory accesses (NMA) per unit time is above a prescribe threshold, the number of levels of speculative branch predictions is reduced per thread for the processor core. Likewise, the number of levels of speculative branch predictions could be increased, from a low level to maximum allowed, if the CPI threshold is exceeded or the number of memory accesses per unit time is below the prescribed threshold.

Abstract: An apparatus for extracting instructions from a stream of undifferentiated instruction bytes in a microprocessor having an instruction set architecture in which the instructions are variable length. Decode logic decodes the instruction bytes of the stream to generate for each a corresponding opcode byte indictor and end byte indicator and receives a corresponding taken indicator for each of the instruction bytes. The taken indicator is true if a branch predictor predicted the instruction byte is the opcode byte of a taken branch instruction. The decode logic generates a corresponding bad prediction indicator for each of the instruction bytes. The bad prediction indicator is true if the corresponding taken indicator is true and the corresponding opcode byte indicator is false. The decode logic sets to true the bad prediction indicator for each remaining byte of an instruction whose opcode byte has a true bad prediction indicator.

Abstract: The present invention provides a system and method for runtime updating of hints in program instructions. The invention also provides for programs of instructions that include hint performance data. Also, the invention provides an instruction cache that modifies hints and writes them back. As runtime hint updates are stored in instructions, the impact of the updates is not limited by the limited memory capacity local to a processor. Also, there is no conflict between hardware and software hints, as they can share a common encoding in the program instructions.

Abstract: Examples of a system, method and computer accessible medium are provided to generate a predicate prediction for a distributed multi-core architecture. Using such system, method and computer accessible medium, it is possible to intelligently encode approximate predicate path information on branch instructions. Using this statically generated information, distributed predicate predictors can generate dynamic predicate histories that can facilitate an accurate prediction of high-confidence predicates, while minimizing the communication between the cores.

Abstract: Embodiments provide methods, apparatus, systems, and computer readable media associated with predicting predicates and branch targets during execution of programs using combined branch target and predicate predictions. The predictions may be made using one or more prediction control flow graphs which represent predicates in instruction blocks and branches between blocks in a program. The prediction control flow graphs may be structured as trees such that each node in the graphs is associated with a predicate instruction, and each leaf associated with a branch target which jumps to another block. During execution of a block, a prediction generator may take a control point history and generate a prediction. Following the path suggested by the prediction through the tree, both predicate values and branch targets may be predicted. Other embodiments may be described and claimed.

Abstract: A processor includes: first selectors that select instruction addresses of instructions of a plurality of threads or a branch target address of a branch instruction to be predicted and that output addresses of the plurality of threads; a second selector that selects one of the addresses of the plurality of threads output by the first selectors; a branch prediction circuit that predicts and outputs a branch direction, which indicates whether the branch instruction of the address selected by the second selector is branched, based on the selected address in a first cycle stage and that predicts and outputs the branch target address of the branch instruction to be predicted based on the selected address in a second cycle stage later than the first cycle stage; and a thread arbitration circuit that controls selection of the addresses of the threads by the first selectors and the second selector.

Abstract: A processor includes: first selectors that select instruction addresses of instructions of a plurality of threads or a branch target address of a branch instruction to be predicted and that output addresses of the plurality of threads; a second selector that selects one of the addresses of the plurality of threads output by the first selectors; a branch prediction circuit that predicts and outputs a branch direction, which indicates whether the branch instruction of the address selected by the second selector is branched, based on the selected address in a first cycle stage and that predicts and outputs the branch target address of the branch instruction to be predicted based on the selected address in a second cycle stage later than the first cycle stage; and a thread arbitration circuit that controls selection of the addresses of the threads by the first selectors and the second selector.

Abstract: The computer system of the present invention emulates target instructions. The computer system includes a processing unit for branching to collective emulation coding for emulating plural of target instructions created beforehand collectively, thereby processing those instructions collectively according to the coding when those target instructions are combined so as to be processed collectively and a memory for storing the collective emulation coding.

Abstract: Techniques are disclosed relating to improving misprediction rates of indirect branch instructions. In one embodiment, a computer system determines misprediction information for an indirect branch instruction included in a sequence of instructions. The misprediction information is indicative of a processor not correctly predicting an actual target address of the indirect branch instruction. In some embodiments, the misprediction information includes a misprediction rate for the target address). Based on the misprediction information, the computer system inserts before the indirect branch instruction a conditional branch instruction that specifies the target address.

Abstract: Systems and methods for predicting out-of-order instruction-level parallelism (ILP) of threads being executed in a multi-threaded processor and prioritizing scheduling thereof are described herein. One aspect provides for tracking completion of instructions using a global completion table having a head segment and a tail segment; storing prediction values for each instruction in a prediction table indexed via instruction identifiers associated with each instruction, a prediction value being configured to indicate an instruction is predicted to issue from one of: the head segment and the tail segment; and predicting threads with more instructions issuing from the tail segment have a higher degree of out-of-order instruction-level parallelism. Other embodiments and aspects are also described herein.

Abstract: A microcontroller using an optimized buffer replacement strategy comprises a memory configured to store instructions, a processor configured to execute said program instructions, and a memory accelerator operatively coupled between the processor and the memory. The memory accelerator is configured to receive an information request and overwrite the buffer from which the prefetch was initiated with the requested information when the request is fulfilled by a previously initiated prefetch operation.

Abstract: A processor of an aspect includes front end logic to process parcels of program code. Each of the parcels has multiple instructions. A branch predictor of the processor is coupled with the front end logic. The branch predictor is to predict directions of branch instructions of the program code. The processor includes jump ahead logic to cause the branch predictor to jump over at least one parcel of the program code that does not have a branch instruction between parcels of the program code that each have at least one branch instruction.

Abstract: A method and apparatus for executing branch instructions is provided. In one embodiment, the method includes receiving a branch instruction, wherein a first path of the branch instruction branches to a target instruction, and wherein a second path of the branch instruction branches to one or more interceding instructions between the branch instruction and the target instruction. The method further includes issuing the one or more interceding instructions and the target instruction and determining if the branch instruction follows the first path or the second path. Upon determining that the branch instruction follows the first path, the one or more interceding instructions between the branch instruction and the target instruction are invalidated.

Abstract: A branch predicting apparatus is disclosed that reduces branch mispredictions in a processor. The branch prediction apparatus includes a base misprediction history register. The branch prediction apparatus includes a meta predictor that receives an index value and a branch prediction to generate a misprediction value in accordance with the base misprediction history register. The branch prediction apparatus also includes a logic gate that receives the branch prediction and the misprediction value to generate a final prediction. The final prediction may be used to predict whether a branch is taken or not taken.

Abstract: An out-of-order execution in-order retire microprocessor includes a branch information table comprising N entries. Each of the N entries stores information associated with a branch instruction. The microprocessor also includes a reorder buffer comprising M entries. Each of the M entries stores information associated with an unretired instruction within the microprocessor. Each of the M entries includes a field that indicates whether the unretired instruction is a branch instruction and, if so, a tag identifying one of the N entries in the branch information table storing information associated with the branch instruction. N is significantly less than M such that the overall die space and power consumption is reduced over a processor in which each reorder buffer entry stores the branch information.

Abstract: Systems, apparatuses, and methods for determinative branch prediction indexing are described herein. The determinative branch prediction indexing method includes receiving a program counter address for a branch instruction, dynamically selecting a branch indexing scheme from a plurality of branch indexing schemes, and generating a branch prediction index based at least in part on selected branch indexing scheme and the program counter address. Other embodiments may be described and claimed.

Abstract: An information handling system employs a processor that includes a thread priority controller. An issue unit in the processor sends branch issue information to the thread priority controller when a branch instruction of an instruction thread issues. In one embodiment, if the branch issue information indicates low confidence in a branch prediction for the branch instruction, the thread priority controller speculatively increases or boosts the priority of the instruction thread containing this low confidence branch instruction. In the manner, should a branch redirect actually occur due to a mispredict, a fetcher is ready to access a redirect address in a memory array sooner than would otherwise be possible.

Abstract: A microprocessor includes a first branch condition state and a second branch condition state. The microprocessor also includes a conditional branch instruction of a first type that instructs the microprocessor to wait to correctly resolve the conditional branch instruction of the first type based on the first branch condition state until other instructions within the microprocessor that update the first branch condition state and that are older than the conditional branch instruction of the first type have updated the first branch condition state. A conditional branch instruction of a second type instructs the microprocessor to correctly resolve the conditional branch instruction of the second type based on the second branch condition state without regard to whether other instructions within the microprocessor that update the second branch condition state and that are older than the conditional branch instruction of the second type have yet updated the second branch condition state.

Abstract: A branch predictor for use in a processor includes a Level 1 branch predictor, a Level 2 branch predictor, a match determining circuit, and an override determining circuit. The Level 1 branch predictor generates a Level 1 branch prediction. The Level 2 branch predictor generates a Level 2 branch prediction. The match determining circuit determines whether the Level 1 and Level 2 branch predictions match. The override determining circuit determines whether to override the Level 1 branch prediction with the Level 2 branch prediction. The Level 1 branch prediction is used when the Level 1 and Level 2 branch predictions match or when the Level 1 and Level 2 branch predictions do not match and the Level 1 branch prediction is not overridden. The Level 2 branch prediction is used when the Level 1 and Level 2 branch predictions do not match and the Level 1 branch prediction is overridden.

Abstract: A bytecode interpreter in a computing system is provided. The interpreter assists in branch prediction by a host processor that processes a virtual machine such as JAVA® and DALVIK®, thereby reducing branch misprediction and achieving high performance.

Abstract: A method, system and computer product for purging pattern history tables as a function of global accuracy in a state machine-based filter gshare branch predictor. An exemplary embodiment includes a method including storing a plurality of encountered branch instructions in the branch history table, indexing the branch history table by a branch instruction address, modifying an entry of the branch history table, indexing the pattern history table, selecting at least one of a branch history entry and a pattern history table entry as a prediction for the branch instruction, wherein the pattern history table entry is selected as the prediction for the branch instruction in response to the branch history entry being in a state specifying to use the pattern history table entry, comparing a pattern history table accuracy to an accuracy threshold, and in response to the pattern history table accuracy falling below the accuracy threshold, purging the PHT.

Abstract: A processor 2 includes instruction decoding circuitry 8 and processing circuitry 16, 18, 20, 22, 24. The instruction decoding circuitry decodes at least one conditional program instruction in accordance with a conditional prediction as one of, in accordance with the condition prediction being a condition pass, one or more micro-operation instructions that control the processing circuitry to perform the processing action together with a condition resolution micro-operation instruction, or in accordance with the condition prediction being a condition fail, at least a condition resolution micro-operation instruction. Condition resolution circuitry 24 responds to the condition resolution micro-operation instruction to determine if the condition prediction is incorrect.

Abstract: A method and apparatus to utilize a branch prediction scheme that limits the expenditure of power and the area consumed caused by branch prediction schemes is provided. The method includes accessing a first entry and a second entry of the data structure, wherein each entry stores a portion of a predicted target address, determining the predicted target address using the portion of the predicted target address stored in the first entry and a portion of a branch address of a fetched branch instruction for a fetched branch instruction of a first type, and determining the predicted target address using the portion of the predicted target address stored in the first entry and the portion of the predicted target address stored in the second entry for a fetched branch instruction of a second type.

Abstract: A system and method for branch prediction in a microprocessor. A hybrid device stores branch prediction information in a sparse cache for no more than a common smaller number of branches within each entry of the instruction cache. For the less common case wherein an i-cache line comprises additional branches, the device stores the corresponding branch prediction information in a dense cache. Each entry of the sparse cache stores a bit vector indicating whether or not a corresponding instruction cache line includes additional branch instructions. This indication may also be used to select an entry in the dense cache for storage. A second sparse cache stores entire evicted entries from the first sparse cache.

Abstract: Techniques are disclosed relating to improving the performance of branch prediction in processors. In one embodiment, a processor is disclosed that includes a branch prediction unit configured to predict a sequence of instructions to be issued by the processor for execution. The processor also includes a pattern detection unit configured to detect a pattern in the predicted sequence of instructions, where the pattern includes a plurality of predicted instructions. In response to the pattern detection unit detecting the pattern, the processor is configured to switch from issuing instructions predicted by the branch prediction unit to issuing the plurality of instructions. In some embodiments, the processor includes a replay unit that is configured to replay fetch addresses to an instruction fetch unit to cause the plurality of predicted instructions to be issued.

Abstract: Various embodiments of the present invention provide systems and methods for branch prediction. As an example, some embodiments of the present invention provides processor circuits that include a program address circuit, a branch target buffer, a branch prediction replacement circuit, and an execution pipeline. The branch target buffer includes a plurality of entries each associated with a respective change of flow instruction. Each entry includes an indication of an entry source and a next program address corresponding to the respective change of flow instruction. The branch prediction replacement circuit is operable to determine replacement priorities of the plurality of entries based at least in part on the entry source for each of the plurality of entries. The execution pipeline receives an executable instruction corresponding to one of the next program addresses.

Abstract: The invention provides a method and apparatus for branch prediction in a processor. A fetch-block branch target buffer is used in an early stage of pipeline processing before the instruction is decoded, which stores information about a control transfer instruction for a “block” of instruction memory. The block of instruction memory is represented by a block entry in the fetch-block branch target buffer. The block entry represents one recorded control-transfer instruction (such as a branch instruction) and a set of sequentially preceding instructions, up to a fixed maximum length N. Indexing into the fetch-block branch target buffer yields an answer whether the block entry represents memory that contains a previously executed a control-transfer instruction, a length value representing the amount of memory that contains the instructions represented by the block, and an indicator for the type of control-transfer instruction that terminates the block, its target and outcome.

Abstract: Predictive decoding is achieved by fetching an instruction, accessing a predictor containing predictor information including prior instruction execution characteristics, obtaining predictor information for the fetched instruction from the predictor; and generating a selected one of a plurality of decode operation streams corresponding to the fetched instruction. The decode operation stream is selected based on the predictor information.

Abstract: A technology for reducing pipeline a control hazard is provided. A conditional branch is processed through a conditional branch prediction, and a predetermined conditional branch prediction, which is determined as incorrect, may be modified through a following test for the conditional branch prediction, thereby reducing the pipeline control hazard quickly without additional hardware.

Abstract: Provided is a processor including an instruction issue unit that issues a vector load instruction read from a main memory based on branch target prediction of a branch target in a branch instruction, a data acquisition unit that starts issue of a plurality of acquisition requests for acquiring a plurality of vector data based on the issued vector load instruction from the main memory, a determination unit that determines a success or a failure of the branch target prediction after the branch target is determined, and a vector load management unit that, when the branch target prediction is determined to be a success, acquires all vector data based on the plurality of acquisition requests and then transfers all the vector data to a vector register, and, when the branch target prediction is determined to be a failure, discards the vector data acquired by the issued acquisition requests.

Abstract: An apparatus to generate a branch prediction of an instruction based at least in part on the address of the previous branch instruction, wherein the previous instruction is prior to the instruction in a program order. The prediction can also based on a branch history value with respect to the previous branch instruction and one or more previous branch predictions.

Abstract: Methods and apparatus to perform efficient indirect branch prediction operations are described. In one embodiment, a branch target buffer (BTB) stored a target address and a bimodal hysteresis counter for an indirect branch that has been encountered by a front-end of the processor during a time period. An indirect branch prediction logic then generates a prediction for an instruction corresponding to a indirect branch based on the stored bimodal hysteresis counter of the BTB. Other embodiments are also claimed and disclosed.

Abstract: A method, apparatus and computer program product are provided for implementing polymorphic branch history table (BHT) reconfiguration. A BHT includes a plurality of predetermined configurations corresponding predetermined operational modes. A first BHT configuration is provided. Checking is provided to identify improved performance with another BHT configuration. The BHT is reconfigured to provide improved performance based upon the current workload.

Abstract: Mechanisms, in a data processing system, are provided for tracking effective addresses through a processor pipeline of the data processing system. The mechanisms comprise logic for fetching an instruction from an instruction cache and associating, by an effective address table logic in the data processing system, an entry in an effective address table (EAT) data structure with the fetched instruction. The mechanisms further comprise logic for associating an effective address tag (eatag) with the fetched instruction, the eatag comprising a base eatag that points to the entry in the EAT and an eatag offset. Moreover, the mechanisms comprise logic for processing the instruction through the processor pipeline by processing the eatag.

Abstract: The present disclosure generally describes computing systems with a multi-core processor comprising one or more branch predictor arrangements. The branch predictor are configured to predict a single and complete flow of program instructions associated therewith and to be performed on at least one processor core of the computing system. Overall processor performance and physical scalability may be improved by the described methods.

Abstract: Declarations from an input source code or tokenized source code are serialized into a stream of tokens produced by following each branch of a preprocessor conditional directive statement that interrupts a declaration. Tokens are labeled with a parsing path indicator corresponding to a parsing path induced by branches of a preprocessor conditional directive. The declarations that are formed along the different parsing paths are serialized by fetching the tokens that belong to the first parsing path in a first pass, and passing the tokens on to a next phase of a compiler. The pointer that marks the next token is repositioned to return to the start of the declaration. The declaration may be serialized again through the second parsing path in a second pass. The operation may be repeated until each of the parsing paths induced by the presence of branches of the preprocessor conditional directives in the source code is exhausted.

Abstract: A system and method for reducing branch misprediction penalty. In response to detecting a mispredicted branch instruction, circuitry within a microprocessor identifies a predetermined condition prior to retirement of the branch instruction. Upon identifying this condition, the entire corresponding pipeline is flushed prior to retirement of the branch instruction, and instruction fetch is started at a corresponding address of an oldest instruction in the pipeline immediately prior to the flushing of the pipeline. The correct outcome is stored prior to the pipeline flush. In order to distinguish the mispredicted branch from other instructions, identification information may be stored alongside the correct outcome. One example of the predetermined condition being satisfied is in response to a timer reaching a predetermined threshold value, wherein the timer begins incrementing in response to the mispredicted branch detection and resets at retirement of the mispredicted branch.

Abstract: A method, data processing system, and computer program product for obtaining information about instructions. Instructions are processed. In response to processing a branch instruction in the instructions, a determination is made as to whether a result from processing the branch instruction follows a prediction of whether a branch is predicted to occur for the branch instruction. In response to the result following the prediction, the branch instruction is added to a current segment in a trace. In response to an absence of the result following the prediction, the branch instruction is added to the current segment in the trace and a first new segment and a second new segment are created. The first new segment includes a first branch instruction reached in the instructions from following the prediction. The second new segment includes a second branch instruction in the instructions reached from not following the prediction.

Abstract: Whenever a link address is written to the link stack, the prior value of the link stack entry is saved, and is restored to the link stack after a link stack push operation is speculatively executed following a mispredicted branch. This condition is detected by maintaining an incrementing tag register which is incremented by each link stack write instruction entering the pipeline, and a snapshot of the incrementing tag register, associated with each branch instruction. When a branch is evaluated and determined to have been mispredicted, the snapshot associated with it is compared to the incrementing tag register. A discrepancy indicates a link stack write instruction was speculatively issued into the pipeline after the mispredicted branch instruction, and pushed a link address onto the link stack, thus corrupting the link stack. The prior link address is restored to the link stack from the link stack restore buffer.

Abstract: A computing system method, program and hardware for correlation of millicode predictions with specific millicode routines receives architected millicode and stores the millicode in internal memory. The computer systems processors' pipeline is employed to predict and select a branch target buffer's (BTB) target address. A computer millicode control enabling an operating system (O/S) multi-task control between multiple user programs able to use millicode routines and ensuring that the programs do not interfere with each other, by use of a branch target buffer (BTB) prediction of a branch target to ensure that a millicode routine does not fetch outside of said millicode routine while performing operations as required by said millicode routing, said branch target buffer prediction employing a correlation mechanism for predicting millicoded branch millicode entry and millicode end instructions and for correlating millicode end predictions with specific millicode routines.

Abstract: In at least one embodiment, an indexed table circuit includes a plurality of banks for storing data to be accessed and a split index array. The indexed table circuit is organized in a plurality of entries each corresponding to a respective one of a plurality of different entry indices, where each entry includes a storage location in the plurality of banks and the split index array. The indexed table circuit further includes selection logic that, responsive to read access of an entry among the plurality of entries utilizing an entry index of a bit string, utilizes a split index read from the split index array to select a set of one or more bits of a tag of the bit string, utilizes the selected set of one or more bits to select data read from one of the plurality of banks, and outputs the selected data.

Abstract: A method of resolving simultaneous branch predictions prior to validation of the predicted branch instruction is disclosed. The method includes processing two or more predicted branch instructions, with each predicted branch instruction having a predicted state and a corrected state. The method further includes selecting one of the corrected states. Should one of the predicted branch instructions be mispredicted, the selected corrected state is used to direct future instruction fetches.

Abstract: Methods, apparatus, and products for branch prediction in a computer processor are disclosed that include: recording for a sequence of occurrences of a branch, in an algorithm in which the branch occurs more than once, each result of the branch, including maintaining a pointer to a location of a most recently recorded result; resetting the pointer to a location of the first recorded result upon completion of the algorithm; and predicting subsequent results of the branch, in subsequent occurrences of the branch, in dependence upon the recorded results.

Abstract: An adaptive prediction threshold scheme for dynamically adjusting prediction thresholds of entries in a Pattern History Table (PHT) by observing global tendencies of the branch or branches that index into the PHT entries. A count value of a prediction state counter representing a prediction state of a prediction state machine for a PHT entry is obtained. Count values in a set of counters allocated to the entry in the PHT are changed based on the count value of the entry's prediction state counter. The prediction threshold of the prediction state machine for the entry may then be adjusted based on the changed count values in the set of counters, wherein the prediction threshold is adjusted by changing a count value in a prediction threshold counter in the entry, and wherein adjusting the prediction threshold redefines predictions provided by the prediction state machine.

Abstract: A method for preventing a return address from being falsified due to a buffer overflow during the program execution, and for detecting the buffer-overflow beforehand. When the return address is re-written during program execution, the debug function of the central processing unit is used to output an error. The falsification of the return address is detected through the error output. Then the falsified return address is re-written to a value stored in advance to enable the program to return to normal operation. When the falsification of the return address is detected, the executing program is terminated.

Abstract: An apparatus and a system, as well as a method and article, may operate to predict a branch within a first operating context, such as a user context, using a first strategy; and to predict a branch within a second operating context, such as an operating system context, using a second strategy. In some embodiments, apparatus and systems may comprise one or more first storage locations to store branch history information associated with a first operating context, and one ore more second storage locations to store branch history information associated with a second operating context.

Abstract: Various embodiments are described relating to processors, branch predictors, branch prediction systems, and computing systems.

Abstract: A branch prediction circuit includes: a memory for storing information representing a branch instruction and a branch prediction; a control circuit for controlling rewriting information in the memory in accordance with a result of determining whether or not a predicted branch has been taken, and determining an attribute of the predicted branch from a branch condition set by the branch instruction and the predicted branch that has been taken, if the predicted branch has been taken; and a rewriting circuit rewriting the information in the memory under the control of the control circuit.

Abstract: A branch prediction method executed in a branch prediction circuit executes the branch instruction, the branch prediction method includes: a branch information storing process for storing the information in the first storage unit or the second storage unit; a process for determining on the basis of a branch condition set by the branch instruction and a realized branch whether the branch prediction is realized; a rewriting process for performing a rewrite of the information in one of the first storage unit and the second storage unit in accordance with the determination and the degree of likelihood that a branch indicated by the branch prediction occurs; and a process for performing branch prediction in response to the branch information when the branch instruction is executed in the processor.

Abstract: A method and system for power conservation in a hierarchical branch predictor system are provided. The method includes addressing multiple branch predictors, each of the branch predictors having various sizes of hierarchical storage and storing information about previously encountered branch instructions. In response to receiving a first branch prediction from one of the branch predictors, the method includes comparing the first branch prediction with previously stored branch predictions to determine the existence of a branch prediction loop, the branch prediction loop including a sequence of branch predictions that repeat as long as constituent predictions of the branches remain unchanged. Upon determining that a branch prediction loop exists, the method includes associating the branch prediction loop with the branch predictors that provided each branch prediction, and activating power saving to the branch predictors that are not associated with the branch prediction loop.