Register Rename Unit Bypasses Zero-Cycle Initialization Latency
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Solution Overview
Problem
Microprocessors face inefficiencies in initializing registers due to control and data dependencies, leading to increased latency and reduced throughput, particularly with instructions like move immediate operations that serialize execution.
Innovation Solution
A processor with a register rename unit that identifies zero cycle operations, such as move immediate instructions, and assigns a physical register number associated with a numerical value, allowing the instruction to be marked complete at the dispatch pipeline stage, thereby bypassing actual register access and reducing resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If register initialization operations (move immediate instructions) are executed through normal pipeline stages, then data dependencies are properly handled, but execution latency increases and throughput decreases
Solution Approach 1:
The patent segments the register initialization operation from the normal execution pipeline by identifying zero-cycle operations (such as move immediate instructions that write constant values) and handling them separately through a dedicated path that bypasses standard pipeline stages, thereby reducing latency without compromising data dependency handling
Solution Approach 2:
The patent performs preliminary identification of zero-cycle operations during the decode or rename stage, determining before execution whether an instruction will write a constant value to a register. This allows the system to prepare the physical register assignment in advance and bypass unnecessary pipeline stages, reducing overall initialization latency
2Loss of energy
If register initialization operations proceed through complete pipeline stages, then resource allocation is proper, but power consumption increases due to unnecessary pipeline stage execution
Solution Approach 1:
The patent divides the instruction execution path into standard pipeline stages for regular operations and a segmented fast path for zero-cycle operations. By separating these paths, the system avoids activating power-consuming pipeline stages for initialization operations, reducing overall power consumption while maintaining proper resource allocation through selective path routing
Solution Approach 2:
The patent applies partial action by executing only the necessary portion of the pipeline for register initialization operations. Instead of completing all standard pipeline stages, the system performs the minimal required actions (decode, rename with constant value assignment, and mark as complete) and skips unnecessary stages, thereby reducing power consumption without compromising correctness
3Productivity
If architectural registers are used for both destination and source operations, then register dependencies are maintained, but instruction serialization occurs reducing parallel execution
Solution Approach 1:
The patent extracts the constant value from the normal register file and places it directly into the physical register assignment logic. For zero-cycle operations, instead of writing to an architectural register and then reading it back, the system directly assigns the constant value to the physical register, eliminating the serialization caused by architectural register dependencies while maintaining data correctness through the renamed register mapping
Solution Approach 2:
The patent introduces the register rename unit as an intermediary between the decode stage and the execution pipeline. This intermediary identifies zero-cycle operations and directly assigns physical registers with constant values, bypassing the architectural register file for these operations. The rename unit acts as a mediator that maintains data dependency correctness through renaming while enabling parallel execution by eliminating serialization bottlenecks
Data Source
AI summary
A system and method for efficiently reducing the latency of initializing registers. A register rename unit within a processor determines whether prior to an execution pipeline stage it is known a decoded given instruction writes a particular numerical value in a destination operand. An example is a move immediate instruction that writes a value of 0 in its destination operand. Other examples may also qualify. If the determination is made, a given physical register identifier is assigned to the destination operand, wherein the given physical register identifier is associated with the particular numerical value, but it is not associated with an actual physical register in a physical register file. The given instruction is marked to prevent it from proceeding to an execution pipeline stage. When the given physical register identifier is used to read the physical register file, no actual physical register is accessed.