Abstract: Techniques for executing versioned memory access instructions. In one embodiment, a processor is configured to execute versioned store instructions of a first thread within a first mode of operation. In this embodiment, in the first mode of operation, the processor is configured to retire a versioned store instruction only after a version comparison has been performed for the versioned store instruction. In this embodiment the processor is configured to suppress retirement of instructions in the first thread that are younger than an oldest versioned store instruction until the oldest versioned store instruction has retired. In some embodiments, the processor is configured to execute versioned store instructions of a given thread within a second mode of operation, in which the processor is configured to retire outstanding versioned store instructions before a version comparison has been performed.

Abstract: Techniques for executing versioned memory access instructions. In one embodiment, a processor is configured to execute versioned store instructions of a first thread within a first mode of operation. In this embodiment, in the first mode of operation, the processor is configured to retire a versioned store instruction only after a version comparison has been performed for the versioned store instruction. In this embodiment the processor is configured to suppress retirement of instructions in the first thread that are younger than an oldest versioned store instruction until the oldest versioned store instruction has retired. In some embodiments, the processor is configured to execute versioned store instructions of a given thread within a second mode of operation, in which the processor is configured to retire outstanding versioned store instructions before a version comparison has been performed.

Abstract: Systems and methods for efficient thread arbitration in a threaded processor with dynamic resource allocation. A processor includes a resource shared by multiple threads. The resource includes entries which may be allocated for use by any thread. Control logic detects long latency instructions. Long latency instructions have a latency greater than a given threshold. One example is a load instruction that has a read-after-write (RAW) data dependency on a store instruction that misses a last-level data cache. The long latency instruction or an immediately younger instruction is selected for replay for an associated thread. A pipeline flush and replay for the associated thread begins with the selected instruction. Instructions younger than the long latency instruction are held at a given pipeline stage until the long latency instruction completes. During replay, this hold prevents resources from being allocated to the associated thread while the long latency instruction is being serviced.

Abstract: Various techniques for mitigating dependencies between groups of instructions are disclosed. In one embodiment, such dependencies include “evil twin” conditions, in which a first floating-point instruction has as a destination a first portion of a logical floating-point register (e.g., a single-precision write), and in which a second, subsequent floating-point instruction has as a source the first portion and a second portion of the same logical floating-point register (e.g., a double-precision read). The disclosed techniques may be applicable in a multithreaded processor implementing register renaming. In one embodiment, a processor may enter an operating mode in which detection of evil twin “producers” (e.g., single-precision writes) causes the instruction sequence to be modified to break potential dependencies. Modification of the instruction sequence may continue until one or more exit criteria are reached (e.g., committing a predetermined number of single-precision writes).

Abstract: Techniques for handling dependency conditions, including evil twin conditions, are disclosed herein. An instruction may designate a source register comprising two portions. The source register may be a double-precision register and its two portions may be single-precision portions, each specified as destinations by two other single-precision instructions. Execution of these two single-precision instructions, especially on a register renaming machine, may result in the appropriate values for the two portions of the source register being stored in different physical locations, which can complicate execution of an instruction stream. In response to detecting a potential dependency, one or more instructions may be inserted in an instruction stream to enable the appropriate values to be stored within one physical double precision register, eliminating an actual or potential evil twin dependency.

Abstract: Techniques for handling dependency conditions, including evil twin conditions, are disclosed herein. An instruction may designate a source register comprising two portions. The source register may be a double-precision register and its two portions may be single-precision portions, each specified as destinations by two other single-precision instructions. Execution of these two single-precision instructions, especially on a register renaming machine, may result in the appropriate values for the two portions of the source register being stored in different physical locations, which can complicate execution of an instruction stream. In response to detecting a potential dependency, one or more instructions may be inserted in an instruction stream to enable the appropriate values to be stored within one physical double precision register, eliminating an actual or potential evil twin dependency.

Abstract: Systems and methods for efficient thread arbitration in a processor. A processor comprises a multi-threaded resource. The resource may include an array of entries which may be allocated by threads. A thread arbitration table corresponding to a given thread stores a high and a low threshold value in each table entry. A thread history shift register (HSR) indexes the table, wherein each bit of the HSR indicates whether the given thread is a thread hog. When the given thread has more allocated entries in the array than the high threshold of the table entry, the given thread is stalled from further allocating array entries. Similarly, when the given thread has fewer allocated entries in the array than the low threshold of the selected table entry, the given thread is permitted to allocate entries. In this manner, threads that hog dynamic resources can be mitigated such that more resources are available to other threads that are not thread hogs.

Abstract: Techniques for handling dependency conditions, including evil twin conditions, are disclosed herein. An instruction may designate a source register comprising two portions. The source register may be a double-precision register and its two portions may be single-precision portions, each specified as destinations by two other single-precision instructions. Execution of these two single-precision instructions, especially on a register renaming machine, may result in the appropriate values for the two portions of the source register being stored in different physical locations, which can complicate execution of an instruction stream. In response to detecting a potential dependency, one or more instructions may be inserted in an instruction stream to enable the appropriate values to be stored within one physical double precision register, eliminating an actual or potential evil twin dependency.

Abstract: Systems and methods for efficient thread arbitration in a processor. A processor comprises a multi-threaded resource. The resource may include an array 8of entries which may be allocated by threads. A thread arbitration table corresponding to a given thread stores a high and a low threshold value in each table entry. A thread history shift register (HSR) indexes the table, wherein each bit of the HSR indicates whether the given thread is a thread hog. When the given thread has more allocated entries in the array than the high threshold of the table entry, the given thread is stalled from further allocating array entries. Similarly, when the given thread has fewer allocated entries in the array than the low threshold of the selected table entry, the given thread is permitted to allocate entries. In this manner, threads that hog dynamic resources can be mitigated such that more resources are available to other threads that are not thread hogs.

Abstract: Techniques for handling dependency conditions, including evil twin conditions, are disclosed herein. An instruction may designate a source register comprising two portions. The source register may be a double-precision register and its two portions may be single-precision portions, each specified as destinations by two other single-precision instructions. Execution of these two single-precision instructions, especially on a register renaming machine, may result in the appropriate values for the two portions of the source register being stored in different physical locations, which can complicate execution of an instruction stream. In response to detecting a potential dependency, one or more instructions may be inserted in an instruction stream to enable the appropriate values to be stored within one physical double precision register, eliminating an actual or potential evil twin dependency.

Abstract: Various techniques for mitigating dependencies between groups of instructions are disclosed. In one embodiment, such dependencies include “evil twin” conditions, in which a first floating-point instruction has as a destination a first portion of a logical floating-point register (e.g., a single-precision write), and in which a second, subsequent floating-point instruction has as a source the first portion and a second portion of the same logical floating-point register (e.g., a double-precision read). The disclosed techniques may be applicable in a multithreaded processor implementing register renaming. In one embodiment, a processor may enter an operating mode in which detection of evil twin “producers” (e.g., single-precision writes) causes the instruction sequence to be modified to break potential dependencies. Modification of the instruction sequence may continue until one or more exit criteria are reached (e.g., committing a predetermined number of single-precision writes).