Instruction Predecoding Circuitry for Cache Macro-Operation Analysis
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Solution Overview
Problem
Current data processing systems face inefficiencies in decoding program instructions due to the lack of predecoding operations, which can lead to increased power consumption and reduced performance, especially in handling macro-operations and branch instructions.
Innovation Solution
Incorporating predecoding circuitry to perform operations such as generating predecode information indicative of macro-operation counts and branch presence, which is stored in the instruction cache to assist the decoding circuitry, allowing for reduced logic complexity and power savings by performing these operations ahead of the critical decode stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If predecoding circuitry is added to generate predecode information before the decode stage, then decoding performance and processing efficiency are improved, but device complexity increases due to additional circuitry
Solution Approach 1:
The predecoding circuitry performs preliminary analysis of instruction blocks to generate predecode information (such as macro-operation counts and branch instruction indicators) before the main decode stage. This preliminary action reduces the workload on the decode stage by pre-processing instructions and storing relevant information in the instruction cache, thereby improving decoding performance while managing complexity through early computation.
2Device complexity
If the decode stage processes all instructions without predecoding assistance, then device complexity is reduced, but power consumption increases due to higher load on the decode stage
Solution Approach 1:
The predecoding circuitry performs preliminary analysis of instruction blocks to generate predecode information (such as macro-operation counts and branch instruction indicators) before the main decode stage. This preliminary action reduces the workload on the decode stage by pre-processing instructions and storing relevant information in the instruction cache, thereby improving decoding performance while managing complexity through early computation.
3Speed
If predecode information is stored in the instruction cache for each instruction block, then decoding speed is improved, but the area of the instruction cache increases
Solution Approach 1:
The predecoding circuitry generates selective predecode information (such as macro-operation counts and branch instruction indicators) rather than complete decoding results for all instructions. This partial processing approach provides sufficient information to accelerate the decode stage without requiring the instruction cache to store excessive data, thus balancing decoding speed improvement with acceptable cache area increase.
Data Source
AI summary
An apparatus comprises processing circuitry, an instruction cache, decoding circuitry to decode program instructions fetched from the cache to generate macro-operations to be processed by the processing circuitry, and predecoding circuitry to perform a predecoding operation on a block of program instructions fetched from a data store to generate predecode information to be stored to the cache with the block of instructions. In one example the predecoding operation comprises generating information on how many macro-operations are to generated by the decoding circuitry for a group of one or more program instructions. In another example the predecoding operation comprises generating information indicating whether at least one of a given subset of program instructions within the prefetched block is a branch instruction.