Branch Target Buffer with Auxiliary Indirect Cache for Branch Prediction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern processors face inefficiencies in branch prediction, particularly in RISC architectures, due to pipeline stalls caused by unresolved branch instructions, which can lead to reduced performance and increased clock cycles when mispredictions occur.
Innovation Solution
Implementing a branch target buffer (BTB) and an indirect branch target buffer (BTBI) within the processor core, utilizing a hashed program counter and branch history information for efficient branch prediction, allowing for both relative and absolute/indirect branching, thereby reducing pipeline flushes and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single branch target buffer is used for all branch types, then the device complexity is reduced, but the branch prediction accuracy deteriorates for indirect branches
Solution Approach 1:
The branch prediction structure is segmented into two separate buffers: a primary branch target buffer for direct branches and an indirect branch target buffer for indirect branches. This segmentation allows each buffer to be optimized for its specific branch type, improving prediction accuracy without excessive complexity increase.
Solution Approach 2:
An intermediary mechanism is introduced to determine which buffer to access based on the branch type. The system uses an indirect branch indicator to select between the primary and indirect buffers, acting as a mediator that routes different branch types to their appropriate prediction structures.
2Device complexity
If branch prediction is not used, then the device complexity is reduced, but the processor performance deteriorates due to pipeline stalls
Solution Approach 1:
The branch target buffers store pre-calculated target addresses for branch instructions. By having these addresses readily available in the buffers before execution, the processor can continue pipeline operations without stalls, as the target address is already prepared and stored.
Solution Approach 2:
The system uses branch history information as feedback to improve prediction accuracy. Historical branch outcomes are stored and used to inform future predictions, creating a feedback loop that continuously improves processor performance by learning from past execution patterns.
3Measurement precision
If a comprehensive branch target buffer is used for all branch types, then the branch prediction accuracy is improved, but the loss of time for buffer searches increases
Solution Approach 1:
The buffer search time is reduced by segmenting the search space into two smaller, specialized buffers. Instead of searching through a large comprehensive buffer, the system performs targeted searches in either the primary or indirect buffer based on the branch type, significantly reducing average search time.
Solution Approach 2:
The buffer structure is pre-organized with dedicated regions for different branch types. This preliminary organization allows the system to directly access the appropriate buffer without performing extensive searches, as the target location is determined in advance by the branch type classification.
Data Source
AI summary
Disclosed embodiments provide techniques for branch prediction. A processor core is accessed. The processor core is coupled to memory and includes branch prediction circuitry. The branch prediction circuitry includes a branch target buffer (BTB) and an indirect branch target buffer (BTBI). A hashed program counter within the processor core is read. The BTB and BTBI are searched. The searching the BTB is accomplished with the hashed program counter and the searching the BTBI is accomplished with the hashed program counter and branch history information. A predicted branch target address within the BTBI or the BTB is matched. The matching within the BTBI is based on an indirect branch instruction, and the matching within the BTB is based on other branch instruction types. The predicted branch target address that was matched is predicted taken. The processor core is directed to fetch a next instruction from the predicted branch target address.