Register Renaming Duplicate Detection via Content-Addressable Memory
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Solution Overview
Problem
Existing processor architectures face challenges in efficiently managing register renaming, particularly with zero-cycle moves, as they struggle to accurately track and manage duplicate references to physical registers, leading to increased circuit area and power consumption.
Innovation Solution
The implementation of a system that uses a content-addressable memory circuit to check the map table for duplicates after rename updates, combined with a rename history file to track safe returns of physical registers to the free list, allowing for efficient detection and management of duplicate references without separate reference counting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If physical register renaming is used to implement zero-cycle moves by mapping multiple architectural registers to the same physical register, then move instruction execution time is reduced to zero cycles, but tracking and managing duplicate references increases circuit area and power consumption
Solution Approach 1:
The patent uses a content-addressable memory (CAM) to store and search for duplicate physical register references. Instead of complex reference counting circuits, the system creates copies of physical register identifiers in the CAM table and searches for matches to detect duplicates. This copying approach enables efficient duplicate detection with reduced circuit area compared to traditional reference counting mechanisms.
Solution Approach 2:
The patent replaces mechanical reference counting circuits with a content-addressable memory-based detection system. The CAM structure provides parallel search capability that substitutes for sequential counting logic, reducing both circuit area and power consumption while maintaining the ability to track duplicate references to physical registers.
2Loss of time
If physical register renaming is used to implement zero-cycle moves by mapping multiple architectural registers to the same physical register, then move instruction execution time is reduced to zero cycles, but tracking and managing duplicate references increases power consumption
Solution Approach 1:
The system creates copies of physical register identifiers in the CAM table to enable parallel search for duplicate detection. This copying mechanism replaces energy-intensive reference counting circuits with a more efficient CAM-based approach that consumes less power while achieving the same duplicate detection function.
Solution Approach 2:
The patent substitutes mechanical reference counting logic with a content-addressable memory system that requires less power. The CAM structure enables parallel comparison operations that are more energy-efficient than sequential counting circuits, reducing overall power consumption while maintaining duplicate detection capability.
3Reliability
If duplicate detection is implemented using traditional reference counting, then duplicate references can be tracked, but device complexity and circuit area increase
Solution Approach 1:
The patent stores copies of physical register identifiers in the CAM table, enabling duplicate detection through parallel search operations. This copying approach simplifies the detection logic compared to traditional reference counting, reducing device complexity while maintaining reliable tracking of duplicate references.
Solution Approach 2:
The system replaces complex reference counting circuits with a content-addressable memory structure that provides simpler, parallel search capability. This substitution reduces device complexity by eliminating the need for intricate counting logic while maintaining the reliability of duplicate reference tracking.
4Reliability
If separate reference counting is used to track physical register references, then duplicate detection is possible, but additional circuit area is required
Solution Approach 1:
The patent merges the duplicate detection function with the existing map table structure by using a content-addressable memory. Instead of adding separate reference counting circuits, the system combines detection capabilities into the existing register renaming infrastructure, reducing additional circuit area requirements while maintaining reliable duplicate detection.
Solution Approach 2:
The system creates copies of physical register identifiers in the CAM table to enable duplicate detection. This copying approach eliminates the need for separate reference counting circuits, reducing circuit area while maintaining the capability to detect duplicate references to physical registers.
Data Source
AI summary
Systems and methods are disclosed for duplicate detection for register renaming. For example, a method includes checking a map table for duplicates of a first physical register, wherein the map table stores entries that each map an architectural register of an instruction set architecture to a physical register of a microarchitecture and a duplicate is two or more architectural registers that are mapped to a same physical register; and, responsive to a duplicate of the first physical register in the map table, preventing the first physical register from being added to a free list upon retirement of an instruction that renames an architectural register that was previously mapped to the first physical register to a different physical register, wherein the free list stores entries that indicate which physical registers are available for renaming.