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1. (WO2016193654) DÉTERMINATION D’UN COMPORTEMENT PRÉDIT POUR LE TRAITEMENT D’INSTRUCTIONS
Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

CLAIMS

1 . An apparatus comprising:

processing circuitry to process instructions;

prediction circuitry to determine, in dependence on current prediction policy information, a predicted behaviour to be used when processing instructions, and to update the current prediction policy information based on an outcome of processing of instructions by the processing circuitry; and

a storage structure to store at least one entry identifying previous prediction policy information for a corresponding block of instructions;

wherein in response to an instruction from a block of instructions for which the storage structure stores a corresponding entry identifying the previous prediction policy information, the prediction circuitry is configured to reset the current prediction policy information based on the previous prediction policy information identified in the corresponding entry of the storage structure.

2. The apparatus according to claim 1 , wherein the processing circuitry has a plurality of processing modes with different performance or energy consumption characteristics; and the predicted behaviour comprises a prediction of which of the plurality of processing modes to use for processing instructions.

3. The apparatus according to claim 2, wherein in one of said plurality of modes, the processing circuitry has a greater maximum throughput of instructions than in another of said plurality of modes.

4. The apparatus according to any preceding claim, wherein the predicted behaviour comprises a predicted outcome of a branch instruction.

5. The apparatus according to any preceding claim, wherein the predicted behaviour comprises a prediction of which data to prefetch from a cache or memory.

6. The apparatus according to any preceding claim, wherein the processing circuitry comprises a fetch stage to fetch instructions from an instruction cache or memory for processing by the processing circuitry; and

the prediction circuitry is configured to reset the current prediction policy information based on the previous prediction policy information in response to the fetch stage fetching an instruction from a block of instructions for which the storage structure stores a corresponding entry identifying the previous prediction policy information.

7. The apparatus according to any preceding claim, wherein each entry of the storage structure comprises the previous prediction policy information and a valid indication indicating whether the previous prediction policy information of that entry is valid; and

the prediction circuitry is configured to reset the current prediction policy information based on the previous prediction policy information in response to an instruction from a block of instructions for which the valid indication of the corresponding entry indicates that the previous prediction policy information is valid.

8. The apparatus according to any preceding claim, wherein the prediction circuitry is configured to set the previous prediction policy information of the entry corresponding to a current block of instructions in dependence on the current prediction policy information, in response to detecting that a predetermined condition is satisfied.

9. The apparatus according to claim 8, wherein the prediction circuitry is configured to maintain a confidence indication indicative of a level of confidence that a prediction based on the current prediction policy information is correct; and

the predetermined condition is satisfied when the level of confidence indicated by the confidence indication exceeds a predetermined threshold.

10. The apparatus according to claim 9, wherein the predetermined condition is satisfied when the level of confidence indicated by the confidence indication exceeds the predetermined threshold and the predicted behaviour determined based on the current prediction policy information has changed since a preceding instance when the predetermined condition was satisfied.

1 1 . The apparatus according to any of claims 8 to 10, wherein in response to detecting that the predetermined condition is satisfied, when the entry corresponding to the current block of instructions already indicates valid previous prediction policy information which is different to the previous prediction policy information which would be set based on the current prediction policy information, the prediction circuitry is configured to invalidate the previous prediction policy information of the entry corresponding to the current block of instructions.

12. The apparatus according to any of claims 8 to 10, wherein said at least one entry comprises a previous prediction confidence indication indicative of a level of confidence that the previous prediction policy information of that entry is correct;

in response to detecting that the predetermined condition is satisfied, when the entry corresponding to the current block of instructions already indicates valid previous prediction policy information which is different to the previous prediction policy information which would be set based on the current prediction policy information, the prediction circuitry is configured to reduce the level of confidence indicated by the previous prediction confidence indication of that entry; and

in response to the previous prediction confidence indication for an entry of the storage structure indicating a level of confidence less than a predetermined threshold, the prediction circuitry is configured to invalidate the previous prediction policy information of that entry.

13. The apparatus according to any preceding claim, wherein the storage structure comprises an instruction cache comprising at least one entry comprising a block of one or more instructions and the previous prediction policy information for that block of one or more instructions.

14. The apparatus according to any preceding claim, wherein the storage structure comprises at least one translation lookaside buffer (TLB) comprising at least one entry comprising address translation information for translating addresses within a corresponding page of addresses and the previous prediction policy information for a block of instructions having addresses within the corresponding page.

15. The apparatus according to claim 14, wherein the storage structure comprises at least a first level TLB and a second level TLB each for storing at least one entry comprising the address translation information and the previous prediction policy information;

wherein the prediction circuitry is configured to update the previous prediction policy information of an entry of the first level TLB; and

the second level TLB is configured to update the previous prediction policy information of an entry of the second level TLB in response to eviction of the corresponding entry of the first level TLB.

16. The apparatus according to claim 15, wherein on allocating an entry to the first level TLB, when the corresponding entry of the second level TLB comprises the previous prediction policy information, the first level TLB is configured to write the previous prediction policy information of the corresponding entry of the second level TLB to the allocated entry of the first TLB.

17. The apparatus according to any of claims 14 to 16, comprising circuitry to update a page table entry of at least one page table with the previous prediction policy information when the corresponding entry is evicted from said at least one TLB.

18. The apparatus according to claim 17, wherein on allocating a new entry to said at least one TLB based on a corresponding page table entry of said at least one page table, when the corresponding page table entry comprises the previous prediction policy information, the at least one TLB is configured to write the previous prediction policy information of the corresponding page table entry to the allocated entry in the at least one TLB.

19. An apparatus comprising:

means for processing instructions;

means for determining, in dependence on current prediction policy information, a predicted behaviour to be used when processing instructions, and updating the current prediction policy information based on an outcome of processing of instructions by the processing circuitry; and

means for storing at least one entry identifying previous prediction policy information for a corresponding block of instructions;

wherein in response to an instruction from a block of instructions for which the means for storing stores a corresponding entry identifying the previous prediction policy information, the means for determining is configured to reset the current prediction policy information based on the previous prediction policy information identified in the corresponding entry of the means for storing.

20. A method comprising:

determining, in dependence on current prediction policy information, a predicted behaviour to be used when processing instructions;

updating the current prediction policy information based on an outcome of processing of instructions by the processing circuitry;

storing in a storage structure at least one entry identifying previous prediction policy information for a corresponding block of instructions; and

in response to an instruction from a block of instructions for which the storage structure stores a corresponding entry identifying the previous prediction policy information, resetting the current prediction policy information based on the previous prediction policy information identified in the corresponding entry of the storage structure.