Target Buffer Address Region Tracking for Branch Prediction
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Solution Overview
Problem
Current branch target prediction methods in computer processors face inefficiencies due to pipeline stalls caused by conditional branch instructions, as they wait for branch resolution before fetching the next instruction, leading to performance losses and increased cycle time.
Innovation Solution
Implementing a target buffer address region tracking system that compares restart addresses to stored addresses to determine 'same' and 'different' address ranges, allowing for accurate prediction of branch targets without waiting for execution stage completion, thereby preventing pipeline stalls and improving instruction throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the processor waits for the conditional branch instruction to be resolved in the execution stage before fetching the next instruction, then the branch target can be accurately computed, but pipeline stalls occur and instruction throughput decreases
Solution Approach 1:
The patent applies preliminary action by performing branch target prediction before the branch instruction is fully executed. The branch target buffer stores predicted target addresses that are computed in advance during the fetch or decode stage, allowing the pipeline to proceed without waiting for the execution stage to resolve the branch condition. This enables the next instruction to be fetched before the current branch is fully resolved, eliminating pipeline stalls while maintaining accurate branch target computation.
2Productivity
If branch target prediction is performed without waiting for execution stage completion, then pipeline stalls are prevented and instruction throughput improves, but prediction accuracy may deteriorate
Solution Approach 1:
The patent implements feedback by using the branch target buffer to store and retrieve previously computed or predicted branch target addresses. When a branch instruction is encountered, the system checks the BTB for matching branch addresses and uses the stored target information to guide prediction. This feedback mechanism allows the system to learn from previous branch outcomes and improve prediction accuracy over time, while still enabling speculative execution to prevent pipeline stalls.
3Productivity
If the processor uses a branch target buffer to predict branch targets, then pipeline stalls are reduced and execution throughput improves, but additional hardware resources are required
Solution Approach 1:
The patent applies universality by designing the branch target buffer to serve multiple functions within the processor architecture. The BTB not only stores branch target addresses but also provides feedback information about branch patterns and outcomes. It works in conjunction with the fetch unit, decode unit, and execution unit to enable speculative execution, branch prediction, and pipeline management. This multi-functional approach allows a single hardware structure to support multiple critical functions, improving execution throughput while limiting the increase in overall hardware complexity.
Data Source
AI summary
Embodiments relate to target buffer address region tracking. An aspect includes receiving a restart address, and comparing, by a processing circuit, the restart address to a first stored address and to a second stored address. The processing circuit determines which of the first and second stored addresses is identified as a same range and a different range to form a predicted target address range defining an address region associated with an entry in the target buffer. Based on determining that the restart address matches the first stored address, the first stored address is identified as the same range and the second stored address is identified as the different range. Based on determining that the restart address matches the second stored address, the first stored address is identified as the different range and the second stored address is identified as the same range.