Branch Prediction Circuitry for Non-Contiguous Blocks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional branch prediction methods often result in bandwidth wastage due to the assumption that the next block to be executed follows the current block, leading to unnecessary flushes when a branch occurs in the current block, thereby reducing the effective bandwidth of the predictor.
Innovation Solution
The proposed solution involves an apparatus and method that perform simultaneous branch predictions on non-contiguous blocks, using branch sequence circuitry to guide the predictions based on the most recently encountered block, which may contain a predicted taken branch, and updating a lookup table with confidence levels to improve prediction accuracy and reduce flushes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If branch prediction is performed on contiguous blocks (X and X+1), then the predictor structure is simple and easy to implement, but bandwidth is wasted due to unnecessary flushes when a branch occurs in block X
Solution Approach 1:
The patent segments the block selection process by introducing a selection mechanism that chooses between contiguous blocks (X+1) and non-contiguous blocks (Y) based on branch prediction outcomes. This segmentation allows the system to switch between different block prediction strategies, optimizing bandwidth utilization while maintaining implementation feasibility through modular architecture.
Solution Approach 2:
The patent implements dynamic block selection where the predictor adapts its behavior based on runtime conditions. The selection circuitry dynamically determines whether to predict contiguous block X+1 or non-contiguous block Y based on branch outcomes, enabling the system to optimize bandwidth usage in real-time while handling diverse control flow patterns effectively.
2Productivity
If branch prediction is performed on non-contiguous blocks simultaneously, then useful bandwidth of the predictor is improved, but the complexity of the predictor increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing multiple potential target blocks (both contiguous X+1 and non-contiguous Y) in advance. The selection circuitry has pre-prepared the necessary block references and selection logic, enabling rapid switching between different block predictions without adding significant runtime complexity, thus improving bandwidth while controlling complexity.
3Measurement precision
If flush is performed when a branch occurs in block X, then prediction accuracy is maintained, but throughput is reduced due to wasted prediction cycles
Solution Approach 1:
The patent converts the harmful effect of branch-induced flushes into a benefit by using the branch outcome information to intelligently select between contiguous and non-contiguous blocks. Instead of simply flushing and wasting cycles, the system leverages the branch information to guide selection, turning what would be wasted prediction capacity into useful bandwidth by predicting appropriate non-contiguous blocks that are more likely to be executed.
Data Source
AI summary
An apparatus is provided to perform branch prediction in respect of a plurality of instructions divided into a plurality of blocks. Receiving circuitry receives references to at least two blocks in the plurality of blocks. Branch prediction circuitry performs at least two branch predictions at a time. The branch predictions are performed in respect of the at least two blocks and the at least two blocks are non-contiguous.