Zero Cycle Move Register Rename Unit Pipeline Optimization
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Solution Overview
Problem
Microprocessors face inefficiencies in data move operations due to control and data dependencies, leading to increased latency and power consumption, particularly in scenarios involving frequent register-to-register move operations.
Innovation Solution
Implementing a register rename unit that identifies zero cycle move operations by mapping source and destination operands to the same physical register, bypassing the move instruction's value to dependent instructions, and marking it for completion at the dispatch pipeline stage, thereby reducing pipeline processing and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional move operations are used to handle register-to-register data transfers, then data dependency requirements are met, but instruction latency and power consumption increase
Solution Approach 1:
The patent extracts the essential function of move operations (satisfying data dependencies) from the traditional execution pipeline. By identifying that many move operations only need to satisfy WAR/WAW dependencies rather than true RAW dependencies, the invention removes unnecessary pipeline stages and processing steps for these operations, achieving zero-cycle execution for qualifying moves while maintaining correctness for dependencies that require actual data transfer.
Solution Approach 2:
The patent segments move operations into different categories based on their dependency characteristics. It distinguishes between moves that require full pipeline processing (true RAW dependencies) and those that can be optimized (WAR/WAW dependencies). This segmentation allows the processor to apply different execution strategies - traditional multi-cycle processing for some moves and zero-cycle bypass for others - thereby reducing overall latency without compromising correctness.
2Use of energy by moving object
If traditional move operations proceed through full pipeline stages, then data dependency correctness is ensured, but power consumption increases
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of a bypass path that allows data to flow directly from the source register to dependent instructions without completing the full move operation pipeline. This intermediary path is controlled by dependency analysis logic that determines when traditional processing is sufficient and when optimization is safe, thereby reducing power consumption while maintaining data dependency correctness through selective application of the bypass.
3Productivity
If register renaming is applied to all move operations, then parallel execution is enabled, but device complexity and resource usage increase
Solution Approach 1:
The patent applies register renaming and optimization techniques selectively rather than universally. It performs partial renaming only for move operations that qualify for zero-cycle execution, leaving traditional move handling unchanged for operations that require full pipeline processing. This partial application of renaming reduces the complexity burden while still achieving throughput improvements for the subset of operations that benefit most from parallel execution.
Data Source
AI summary
A system and method for reducing the latency of data move operations. A register rename unit within a processor determines whether a decoded move instruction is eligible for a zero cycle move operation. If so, control logic assigns a physical register identifier associated with a source operand of the move instruction to the destination operand of the move instruction. Additionally, the register rename unit marks the given move instruction to prevent it from proceeding in the processor pipeline. Further maintenance of the particular physical register identifier may be done by the register rename unit during commit of the given move instruction.