Embodiments of instructions are detailed herein including one or more of 1) a branch fence instruction, prefix, or variants (BFENCE); 2) a predictor fence instruction, prefix, or variants (PFENCE); 3) an exception fence instruction, prefix, or variants (EFENCE); 4) an address computation fence instruction, prefix, or variants (AFENCE); 5) a register fence instruction, prefix, or variants (RFENCE); and, additionally, modes that apply the above semantics to some or all ordinary instructions.

A computer processor includes a branch prediction unit that includes a local branch predictor and a global branch predictor. Managing power consumption in such a computer processor includes, for each of a plurality of branch instructions: performing, by the local branch predictor, a local branch prediction; performing, by each of the global branch predictors, a global branch prediction; determining to utilize the local branch prediction over the global branch predictions as a branch prediction for the branch instruction; incrementing a value of a counter; determining whether the value of the counter exceeds a predetermined threshold; and if the value of the counter exceeds the predetermined threshold, powering down at least one of the global branch predictors and configuring the branch prediction unit to bypass the powered down global branch predictor for branch predictions of subsequent branch instructions.

Techniques that facilitate heterogeneous runahead processing for a processor core are provided. In one example, a first core performs a first execution of a first sequence of instructions, where the first core is communicatively coupled to a first cache memory. A second core performs a second execution of at least a portion of the first sequence of instructions and a first determination that data associated with the first sequence of instructions fails to be stored in the first cache memory, where the first determination is performed concurrent with the first execution, and the first core executes a second sequence of instructions based on a second determination that the second core is performing the second execution of at least a portion of the first sequence of instructions.

An apparatus includes instruction fetching circuitry to read a set of instructions, including a speculative execution instruction and a speculative condition determination instruction; cache the instructions; and read the speculative execution instruction corresponding to the speculative condition of the speculative condition determination instruction. If an execution result of the speculative condition determination instruction indicates the speculative condition is incorrect, clear the instructions cached in the instruction fetching circuitry. Instruction decoding circuitry decodes instructions. Executing circuitry executes instructions, including executing the speculative condition determination instruction to obtain the execution result. Instruction retiring circuitry caches instructions executed by the executing circuitry, and in response to an instruction older than the speculative condition determination instruction being retired, instructs the executing circuitry to clear instructions in the executing circuitry and clear the instructions cached in the instruction retiring circuitry.

One embodiment of the present invention sets forth a technique for speculatively issuing instructions to allow a processing pipeline to continue to process some instructions during rollback of other instructions. A scheduler circuit issues instructions for execution assuming that, several cycles later, when the instructions reach multithreaded execution units, that dependencies between the instructions will be resolved, resources will be available, operand data will be available, and other conditions will not prevent execution of the instructions. When a rollback condition exists at the point of execution for an instruction for a particular thread group, the instruction is not dispatched to the multithreaded execution units. However, other instructions issued by the scheduler circuit for execution by different thread groups, and for which a rollback condition does not exist, are executed by the multithreaded execution units. The instruction incurring the rollback condition is reissued after the rollback condition no longer exists.

In a computer supporting Transactional Memory (TM) Transaction Execution (TX), use of speculative branch prediction is programmably suspended during TX, and programmably resumed. The branch prediction suspension may cause the execution of one or more instructions following the branch instruction to stall in the pipeline until branch conditions and branch target addresses are resolved.

A data processing apparatus (4) includes processing circuitry (6) for executing program instructions that form part of a transaction which executes to generate speculative updates and to commit the speculative updates if the transaction completes without a conflict. Instruction sampling circuitry (44) captures instruction diagnostic data (IDD) relating to execution of a sampled instruction. Transaction tracking circuitry (46) detects if the sampled instruction is within a transaction and if so, tracks whether the speculative updates associated with the transaction are committed and captures transaction diagnostic data (TDD) indicative of whether or not the speculative updates were committed. Thus, both instruction diagnostic data relating to a sampled instruction and transaction diagnostic data relating to the fate of a transaction containing a sampled instruction are captured.

Speculative execution using a page-level tracked load order queue includes: determining that a first load instruction targets a determined memory region; and in response to the first load instruction targeting the determined memory region, adding an entry to a page-level tracked load order queue instead of a load order queue, where the entry indicates a page address of a target of the first load instruction.

Various embodiments of microprocessors and methods of operating a microprocessor during runahead operation are disclosed herein. One example method of operating a microprocessor includes identifying a runahead-triggering event associated with a runahead-triggering instruction and, responsive to identification of the runahead-triggering event, entering runahead operation and inserting the runahead-triggering instruction along with one or more additional instructions in a queue. The example method also includes resuming non-runahead operation of the microprocessor in response to resolution of the runahead-triggering event and re-dispatching the runahead-triggering instruction along with the one or more additional instructions from the queue to the execution logic.

An apparatus (2) may have a processing element (4) for performing data access operations to access data from at least one storage device (10, 12, 14). The processing element may have at least one transactional processing resource (10, 18) supporting processing of a transaction in which data accesses are performed speculatively following a transaction start event and for which the speculative results are committed in response to a transaction end event. Monitoring circuitry (30) captures monitoring data indicating a degree of utilization of the transactional processing resource (10, 18) when processing the transaction.