Processor Core Store-Load Dependency Circuit for Zero-Cycle Loads
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Solution Overview
Problem
Processor cores face inefficiencies due to the time-consuming nature of store and load instructions, particularly when accessing memory, leading to stalls and reduced performance as load instructions wait for store operations to complete.
Innovation Solution
Implementing a processor core with a store-load dependency circuit that identifies and preserves information related to store instructions, allowing for zero-cycle loads by determining dependencies between store and load instructions, thereby enabling the execution of load instructions without waiting for store operations to finish.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If store instructions are executed sequentially with load instructions waiting for store completion, then data consistency is ensured, but processor performance deteriorates due to execution stalls
Solution Approach 1:
The patent applies preliminary action by identifying store-load pairs and preparing load instructions in advance before store operations complete. The load instruction is decoded and ready to execute as soon as the store finishes, eliminating unnecessary stalls and allowing the processor to maintain high performance while ensuring data consistency through proper dependency tracking
Solution Approach 2:
The patent implements feedback mechanisms through dependency tracking circuits that monitor store instruction completion status and feed this information back to load instructions. This allows the system to dynamically adjust execution timing, ensuring loads only execute after their corresponding stores are complete, thus maintaining data consistency without unnecessary delays
2Reliability
If load instructions wait for store operations to complete, then data correctness is maintained, but execution time increases
Solution Approach 1:
The patent applies preliminary action by pre-decoding load instructions and preparing them for immediate execution once store operations complete. The load instruction is ready in advance, so as soon as the store finishes, the load can execute without waiting for additional cycles, thereby reducing execution time while maintaining data correctness through dependency tracking
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the processor in a state where instructions are continuously decoded and prepared. Load instructions are kept ready in a buffer, and as soon as store operations complete, the pipeline continues executing without idle cycles, thus eliminating time loss while preserving data correctness
3Productivity
If store instructions are buffered in a queue, then instruction throughput is improved, but complexity of dependency management increases
Solution Approach 1:
The patent applies segmentation by dividing the dependency management function into separate circuit components: a store-load dependency circuit that identifies pairs, a buffer that stores instruction information, and execution logic that handles loads. This modular approach improves throughput by allowing parallel processing while managing complexity through functional decomposition
Solution Approach 2:
The patent introduces an intermediary store-load dependency circuit that acts as a mediator between store and load instructions. This circuit buffers store information and provides it to load instructions when ready, simplifying dependency management by centralizing the coordination function in a dedicated circuit rather than requiring complex distributed management
Data Source
AI summary
An apparatus includes a processor core that includes an instruction decode circuit and a control circuit. The instruction decode circuit is configured to decode instructions, including a plurality of store instructions used to store information in a memory hierarchy. The control circuit is configured, after a particular store instruction is decoded, to preserve store information related to the particular store instruction, including a first program counter value for the particular store instruction. In response to decoding a subsequent load instruction with a corresponding second program counter value, the control circuit is configured to determine, using the first and second program counter values, whether a dependency has been established between the subsequent load instruction and the particular store instruction. In response to a determination that the dependency has been established, the control circuit is configured to use the preserved store information to perform the subsequent load instruction.