Vector Micro-operation Replacement for Pipeline Flush Avoidance
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Solution Overview
Problem
Existing data processing techniques for vector operands often waste resources when all elements in a vector register portion are non-selected, as they require additional guarding branch instructions that can lead to branch mispredictions and performance degradation.
Innovation Solution
A data processing apparatus and method that detects whether control information indicates no selected elements in a source vector register portion, allowing for either processing the original vector micro-operation if elements are selected or replacing it with a lower-latency micro-operation if not, eliminating the need for guarding branch instructions and optimizing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If guarding branch instructions are used to detect whether selected elements exist in vector register portion, then processing correctness is ensured, but pipeline flushes due to branch mispredictions occur and performance degrades
Solution Approach 1:
The patent extracts the detection of zero-length micro-operations from the normal execution flow and handles them separately through replacement with alternative micro-operations. This removes the need for guarding branch instructions that cause pipeline flushes, thereby maintaining processing correctness while eliminating performance degradation.
Solution Approach 2:
The control circuitry performs preliminary detection of zero-length micro-operations before they enter the main execution pipeline. By identifying and replacing these operations in advance with alternative micro-operations having the same effect, the system prevents pipeline flushes and maintains high processing performance while ensuring correctness.
2Device complexity
If original vector micro-operation is processed even when no elements are selected, then processing simplicity is maintained, but processing resources are wasted and efficiency decreases
Solution Approach 1:
The patent changes the parameter of micro-operation selection based on the detected condition of zero-length operations. When no selected elements are present, the system transitions from processing the original vector micro-operation to processing a replacement micro-operation with lower latency, thereby improving processing efficiency without significantly increasing complexity.
Solution Approach 2:
Instead of always performing the full vector processing operation, the system applies partial action by replacing zero-length micro-operations with alternative operations that have the same effect but lower latency. This avoids unnecessary processing of non-selected elements while maintaining correctness.
3Speed
If replacement micro-operation with lower latency is used when no elements are selected, then processing speed is improved, but additional control logic is required to detect and replace micro-operations
Solution Approach 1:
The patent merges the detection and replacement functionality into the existing control circuitry that already handles micro-operation dispatch. By integrating the zero-length detection and replacement logic with the existing control structure, the system achieves faster processing speed while minimizing the increase in control logic complexity.
Data Source
AI summary
A data processing apparatus has processing circuitry for processing vector operands from a vector register store in response to vector micro-operations, some of which have control information identifying which data elements of the vector operands are selected for processing. Control circuitry detects vector micro-operations for which the control information specifies that a portion of the vector operand to be processed has no selected elements. If this is the case, then the control circuitry controls the processing circuitry to process a lower latency replacement micro-operation instead of the original micro-operation. This provides better performance than if a branch instruction is used to bypass the micro-operation if there are no selected elements.