Branch Status Table and Control Instruction Buffer for Misprediction Recovery
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Solution Overview
Problem
Existing processor architectures face inefficiencies in executing control instructions due to branch mispredictions, leading to suboptimal pipeline performance and resource utilization.
Innovation Solution
Implementing a branch status table and a control instruction buffer to track and store control instruction data entries, ensuring the availability of the appropriate control instructions despite branch mispredictions, while minimizing the size of the branch status table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a traditional branch prediction mechanism is used to handle control instructions, then the pipeline can continue execution during branch resolution, but branch mispredictions cause control instructions to be unwound incorrectly, leading to pipeline errors and performance degradation
Solution Approach 1:
The patent segments control instructions from regular instructions by implementing a separate control instruction buffer. This buffer stores control instructions independently, allowing the pipeline to handle them differently from standard instructions. The segmentation enables the system to track control instructions through branch predictions without risking incorrect unwinding, as they are isolated in their own buffer structure.
Solution Approach 2:
The patent introduces a control instruction buffer as an intermediary structure between the branch prediction mechanism and the execution pipeline. This buffer acts as a mediator that decouples the branch prediction logic from control instruction handling, allowing accurate tracking of control instructions even when branch mispredictions occur. The buffer serves as a buffer zone that prevents erroneous control instruction unwinding while maintaining pipeline flow.
2Reliability
If the branch status table stores complete control instruction information for all possible branches, then misprediction recovery is accurate, but the table size becomes excessively large, increasing hardware complexity and resource usage
Solution Approach 1:
The patent extracts control instruction information from the traditional branch status table and places it into a separate control instruction buffer. This extraction reduces the branch status table to storing only essential branch metadata (target addresses, prediction states), while the detailed control instruction data resides in the dedicated buffer. This separation significantly reduces the branch status table size while maintaining complete control instruction information for accurate misprediction recovery.
Solution Approach 2:
The patent transitions from a two-dimensional branch status table (branch index × status information) to a three-dimensional structure by adding the control instruction buffer as a separate dimension. Control instructions are organized in the buffer with their own addressing scheme, allowing the system to access control instruction data without expanding the branch status table. This dimensional separation enables efficient memory usage while preserving complete control information.
3Productivity
If control instructions are executed speculatively with branch predictions, then pipeline efficiency is improved, but incorrect control instructions may be executed due to mispredictions, requiring complex recovery mechanisms
Solution Approach 1:
The patent implements preliminary action by pre-loading control instructions into the control instruction buffer before they are needed for execution. The buffer is populated with control instructions and their associated metadata in advance, allowing the pipeline to quickly retrieve the correct control instruction during branch resolution without complex recovery operations. This pre-positioning of control instructions simplifies the recovery mechanism by eliminating the need for complex unwinding and re-fetching operations.
Data Source
AI summary
Systems and methods related to a branch status table and control instruction buffer for processor instruction pipeline are disclosed herein. A processor may include a branch status table and a control instruction buffer. The branch status table may be formed by a set of registers and may store a set of pointers that correspond with a set of branches. The control instruction buffer may store a set of instruction pipeline control data entries in a set of addresses. The pointers may identify addresses which store the most recent instruction pipeline control data entries which proceed the branches that correspond with the pointers. Beneficially, when a branch misprediction occurs, the data structure can effectively be rewound to a point just before the misprediction with minimal overhead.