Processor Instruction Lookahead Annotation Logic
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Solution Overview
Problem
Processors face inefficiencies due to delays in accessing memory locations and predicting instruction dependencies, leading to suboptimal execution and parallelism in multi-threaded environments.
Innovation Solution
Incorporating annotation logic to determine a lookahead distance for instructions, which measures register dependence, and using this information to issue instructions only when all predecessors have retired or issued, ensuring correct order and enforcing dependences through explicit dependence lookahead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the processor speculatively predicts instruction dependences to execute instructions in parallel, then instruction level parallelism is improved, but the processor may have to discard incorrectly predicted results and re-execute instructions in the correct order
Solution Approach 1:
The patent applies preliminary action by annotating instructions with dependence information before execution. The annotation logic determines and stores dependence distances for instructions in advance, allowing the issue logic to make informed decisions about instruction issuance without speculative prediction, thereby avoiding the need to discard incorrectly predicted results
Solution Approach 2:
The patent implements feedback by using the annotated dependence information to control instruction issuance. The issue logic uses the stored dependence distances to determine when instructions are ready to be issued, creating a feedback mechanism that ensures correct execution order based on actual dependence relationships rather than speculative predictions
2Reliability
If the processor waits for memory access or instruction completion to maintain correctness, then prediction accuracy is improved, but execution speed deteriorates
Solution Approach 1:
The annotation logic performs preliminary analysis of instruction dependences and stores the results in the instruction cache. This allows the issue logic to quickly determine instruction readiness without waiting for actual memory access or instruction completion, thereby maintaining execution speed while ensuring correctness through pre-computed dependence information
3Productivity
If the processor fetches instructions from a different thread to maintain efficiency during waits, then productivity is improved, but thread management complexity increases
Solution Approach 1:
The patent applies self-service by enabling each thread to independently provide its own readiness information through the annotated dependence distances. The issue logic can efficiently determine which instructions from any thread are ready to be issued based on the pre-stored dependence information, reducing the complexity of cross-thread coordination and management
Data Source
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AI summary
A processor having an instruction cache for storing a plurality of instructions is provided. The processor further includes annotation logic configured to determine a lookahead distance associated with an instruction and annotate the at least one instruction cache with the lookahead distance. The lookahead distance may correspond to a number of instructions that separates an instruction that references a register from the most recent register definition. The lookahead distance may indicate the shortest distance to a later instruction that references a register that this instruction defines.