Sun Microsystems, Inc.

Oracle America, Inc.

Stevan A Vlaovic

Lawrence Spracklen

Santosh Abraham

Robert Cypher

Darryl J Gove

Craig Anderson

Steven R Hart

In one embodiment, the branch prediction mechanism includes a first storage including a first plurality of locations for storing a first set of partial prediction information. The branch prediction mechanism also includes a second storage including a second plurality of locations for storing a second set of partial prediction information. Further, the branch prediction mechanism includes a control unit that performs a first hash function on input branch information to generate a first index for accessing a selected location within the first storage. The control unit also performs a second hash function on the input branch information to generate a second index for accessing a selected location within the second storage. Lastly, the control unit further provides a prediction value based on corresponding partial prediction information in the selected locations of the first and the second storages.

Branch prediction mechanisms using multiple hash functions

Intelligent prediction of critical sections is implemented using a method comprising updating a critical section estimator based on historical analysis of atomic/store instruction pairs during runtime and performing lock elision when the critical section estimator indicates that the atomic/store instruction pairs define a critical section.

Method and apparatus for critical section prediction for intelligent lock elision

RAW aliasing can be predicted with register bypassing based at least in part on execution displacement alias prediction. Repeated aliasing between read and write operations (e.g., within a loop), can be reliably predicted based on displacement between the aliasing operations. Performing register bypassing for predicted to alias operations facilitates faster RAW bypassing and mitigates the performance impact of aliasing read operations. The repeated aliasing between operations is tracked along with register information of the aliasing write operations. After exceeding a confidence threshold, an instance of a read operation is predicted to alias with an instance of a write operation in accordance with the previously observed repeated aliasing. Based on displacement between the instances of the operations, the register information of the write operation instance is used to bypass data to the read operation instance.

Execution displacement read-write alias prediction

Predicting prefetch data sources for runahead execution triggering read operations eliminates the latency penalties of missing read operations that typically are not addressed by runahead execution mechanisms. Read operations that most likely trigger runahead execution are identified. The code unit that includes those triggering read operations is modified so that the code unit branches to a prefetch predictor. The prefetch predictor observes sequence patterns of data sources of triggering read operations and develops prefetch predictions based on the observed data source sequence patterns. After a prefetch prediction gains reliability, the prefetch predictor supplies a predicted data source to a prefetcher coincident with triggering of runahead execution.

Prefetch prediction

A method and apparatus provides the capability for a single function to safely use multiple register windows within the same function, with minimal additional support from the operating system, by specifying a new window pointer, the 'Effective Current Window Pointer' (ECWP), to be used in conjunction with the prior art window pointer. According to the present invention, the new window pointer ECWP can be used to override the prior art window pointer in dictating from which register window the operands stipulated by the instructions to be executed are sourced/sinked. Consequently, using the method and apparatus of the invention, the number of spills to memory is reduced, the number of instructions required is decreased, resources are used more efficiently, and costly dependency problems and RAW (read-after-write) stalls are prevented.

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Cupertino, CA, United States of America

Stevan A Vlaovic