Abstract: A data processing apparatus includes detection circuitry that detects a parent instruction and a child instruction from a stream of instructions. The parent instruction references a destination register that is referenced as a source register by the child instruction. Adjustment circuitry then adjusts the child instruction to produce an adjusted child instruction whose behaviour is logically equivalent to a behaviour of executing the parent instruction followed by the child instruction.

Abstract: A data processing apparatus is provided that comprises rename circuitry for performing a register rename stage of a pipeline in respect of a stream of operations. Move elimination circuitry performs a move elimination operation on the stream of operations in which a move operation is eliminated and the register rename stage performs an adjustment of an identity of registers in the stream of operations to compensate for the move operation being eliminated and demotion circuitry reverses or inhibits the adjustment in response to one or more conditions being met.

Abstract: A data processing apparatus is provided. It includes processing circuitry for speculatively executing a plurality of instructions. Storage circuitry stores a current state of the processing circuitry and a plurality of previous states of the processing circuitry. Execution of the plurality of instructions changes the current state of the processing circuitry. Flush circuitry replaces, in response to a miss-prediction, the current state of the processing circuitry with a replacement one of the plurality of previous states of the processing circuitry.

Abstract: A processing apparatus supporting register renaming is provided with checkpoint circuitry to capture register mapping checkpoints indicative of speculative register mappings between logical registers and physical registers at a given point of speculative execution, and register group tracking circuitry to maintain tracking information for groups of logical registers. The tracking information for a given group indicates whether the given group is a changed group comprising at least one logical register for which a corresponding speculative register mapping has changed since a last checkpoint was captured, or an unchanged group for which none of the logical registers in that group have had their speculative register mappings changed since the last checkpoint was captured. When capturing a new register mapping checkpoint, unchanged groups of logical registers are excluded from the new register mapping checkpoint. This can save power in a register mapping checkpointing scheme.

Abstract: A processing apparatus supporting register renaming is provided with checkpoint circuitry to capture register mapping checkpoints indicative of speculative register mappings between logical registers and physical registers at a given point of speculative execution, and register group tracking circuitry to maintain tracking information for groups of logical registers. The tracking information for a given group indicates whether the given group is a changed group comprising at least one logical register for which a corresponding speculative register mapping has changed since a last checkpoint was captured, or an unchanged group for which none of the logical registers in that group have had their speculative register mappings changed since the last checkpoint was captured. When capturing a new register mapping checkpoint, unchanged groups of logical registers are excluded from the new register mapping checkpoint. This can save power in a register mapping checkpointing scheme.

Abstract: A data processing apparatus is provided. It includes processing circuitry for speculatively executing a plurality of instructions. Storage circuitry stores a current state of the processing circuitry and a plurality of previous states of the processing circuitry. Execution of the plurality of instructions changes the current state of the processing circuitry. Flush circuitry replaces, in response to a miss-prediction, the current state of the processing circuitry with a replacement one of the plurality of previous states of the processing circuitry.

Abstract: Issue logic identifies a simple fixed point instruction, included in a unified payload, which is ready to issue. The simple fixed point instruction is a type of instruction that is executable by both a fixed point execution unit and a load-store execution unit. In turn, the issue logic determines that the unified payload does not include a load-store instruction that is ready to issue. As a result, the issue logic issues the simple fixed point instruction to the load-store execution unit in response to determining that the simple fixed point instruction is ready to issue and determining that the unified payload does not include a load-store instruction that is ready to issue.

Abstract: An information handling system includes a processor with a bifurcated unified issue queue that may perform unified issue queue VSU store instruction dependency operations. The bifurcated unified issue queue BUIQ maintains VSU store instructions in the form of internal operations data. The BUIQ includes a unified issue queue UIQ 0 and a unified issue queue UIQ 1. The BUIQ may manage a particular VSU store instruction from one UIQ to determine data dependencies and employ the other UIQ to determine address dependencies of that particular VSU store instruction. The UIQs employ a dependency matrix including a dependency array. The dependency array data maintains both data and address dependency information. The particular VSU store instruction issues to execution units such as VSUs for data dependency information and load store units (LSUs) for address dependency information. A particular VSU store instruction may execute to provide data dependency information independent of address dependency information.

Abstract: An information handling system includes a processor with an issue unit (IU) that may perform instruction dependency tracking for successive instruction issue operations. The IU maintains non-shifting issue queue (NSIQ) and shifting issue queue (SIQ) instructions along with relative instruction to instruction dependency information. A mapper maps queue position data for instructions that dispatch to issue queue locations within the IU. The IU may test an issuing producer instruction against consumer instructions in the IU for queue position (QPOS) and register tag (RTAG) matches. A matching consumer instruction may issue in a successive manner in the case of a queue position match or in a next processor cycle in the case of a register tag match.

Abstract: An information handling system includes a processor with an issue unit (IU) that may perform instruction dependency tracking for successive instruction issue operations. The IU maintains non-shifting issue queue (NSIQ) and shifting issue queue (SIQ) instructions along with relative instruction to instruction dependency information. A mapper maps queue position data for instructions that dispatch to issue queue locations within the IU. The IU may test an issuing producer instruction against consumer instructions in the IU for queue position (QPOS) and register tag (RTAG) matches. A matching consumer instruction may issue in a successive manner in the case of a queue position match or in a next processor cycle in the case of a register tag match.

Abstract: Issue logic identifies a simple fixed point instruction, included in a unified payload, which is ready to issue. The simple fixed point instruction is a type of instruction that is executable by both a fixed point execution unit and a load-store execution unit. In turn, the issue logic determines that the unified payload does not include a load-store instruction that is ready to issue. As a result, the issue logic issues the simple fixed point instruction to the load-store execution unit in response to determining that the simple fixed point instruction is ready to issue and determining that the unified payload does not include a load-store instruction that is ready to issue.

Abstract: A method and apparatus for register renaming are provides in the illustrative embodiments. A mapper receives a request for a data in a logical register. The mapper searches an in-flight map table and a set of architected map tables for the data in the logical register. The mapper identifies an entry in one of the in-flight map table and an architected map table in the set of architected map tables that corresponds with the logical register in the request. The mapper returns a location of a physical register, which holds the requested data.

Abstract: An information handling system includes a processor with a bifurcated unified issue queue that may perform unified issue queue VSU store instruction dependency operations. The bifurcated unified issue queue BUIQ maintains VSU store instructions in the form of internal operations data. The BUIQ includes a unified issue queue UIQ 0 and a unified issue queue UIQ 1. The BUIQ may manage a particular VSU store instruction from one UIQ to determine data dependencies and employ the other UIQ to determine address dependencies of that particular VSU store instruction. The UIQs employ a dependency matrix including a dependency array. The dependency array data maintains both data and address dependency information. The particular VSU store instruction issues to execution units such as VSUs for data dependency information and load store units (LSUs) for address dependency information. A particular VSU store instruction may execute to provide data dependency information independent of address dependency information.

Abstract: A method is provided for evaluating two or more instructions in an out of order issue queue during a particular cycle of the queue, to select an instruction for issue during the next following cycle. If an instruction was previously designated to issue during the particular cycle, one or more instructions in the queue are evaluated to determine if any of them are dependent on the designated instruction. For the evaluation, each instruction placed into the queue is accompanied by corresponding logic elements that provide destination to source compares for the instruction. In an embodiment comprising a method, the oldest ready instruction in the queue during a particular cycle is identified.

Abstract: The illustrative embodiment is a circuit and method for reversing a linked list of multiple nodes to produce a reversed linked list. The circuit includes a decoder for sequentially decoding multiple original input tags, which are associated with the nodes of the linked list, to produce decoded values, an array for storing the decoded values, and a circuit for reading the array to simultaneously generate the tags that are associated with the nodes of the reversed linked list, where separate encoders are not used.

Abstract: A method and apparatus for register renaming are provides in the illustrative embodiments. A mapper receives a request for a data in a logical register. The mapper searches an in-flight map table and a set of architected map tables for the data in the logical register. The mapper identifies an entry in one of the in-flight map table and an architected map table in the set of architected map tables that corresponds with the logical register in the request. The mapper returns a location of a physical register, which holds the requested data.

Abstract: A method is provided for evaluating two or more instructions in an out of order issue queue during a particular cycle of the queue, to select an instruction for issue during the next following cycle. If an instruction was previously designated to issue during the particular cycle, one or more instructions in the queue are evaluated to determine if any of them are dependent on the designated instruction. For the evaluation, each instruction placed into the queue is accompanied by corresponding logic elements that provide destination to source compares for the instruction. In an embodiment comprising a method, the oldest ready instruction in the queue during a particular cycle is identified.

Abstract: A method is provided for evaluating two or more instructions in an out of order issue queue during a particular cycle of the queue, to select an instruction for issue during the next following cycle. If an instruction was previously designated to issue during the particular cycle, one or more instructions in the queue are evaluated to determine if any of them are dependent on the designated instruction. For the evaluation, each instruction placed into the queue is accompanied by corresponding logic elements that provide destination to source compares for the instruction. In an embodiment comprising a method, the oldest ready instruction in the queue during a particular cycle is identified.

Abstract: The illustrative embodiment is a circuit and method for reversing a linked list of multiple nodes to produce a reversed linked list. The circuit includes a decoder for sequentially decoding multiple original input tags, which are associated with the nodes of the linked list, to produce decoded values, an array for storing the decoded values, and a circuit for reading the array to simultaneously generate the tags that are associated with the nodes of the reversed linked list, where separate encoders are not used.

Abstract: A circuit and method provide rename register reallocation for simultaneous multi-threaded (SMT) processors that redistributes rename (mapped) resources between one thread during single-threaded (ST) execution and multiple threads during multi-threaded execution. The processor receives an instruction specifying a transition from a single-threaded to a multi-threaded mode or vice-versa and halts execution of all threads executing on the processor. The internal control logic then signals the resources to reallocate the resources. Rename resources are reallocated by directing an action at the rename mapper. When switching from SMT to ST mode, the mapper is directed to drop entries for the dying thread, but on a switch from ST to SMT mode, “dummy” instruction group dispatch indications are sent to the mapper that indicate use of all architected registers for each thread.