Deterministic Register Renaming Without Free Lists or History Files
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Solution Overview
Problem
Modern processors face performance degradation due to register conflicts arising from multiple instructions competing for the same register, leading to stalls and inefficiencies in instruction-level parallelism.
Innovation Solution
Implement a register renaming mechanism using counters to deterministically map physical registers to architectural registers, eliminating the need for a free list and history file by utilizing allocation and retirement counters for reserved architectural registers, thereby ensuring efficient and monotonic mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional register allocation methods are used with free lists and history files, then register mapping flexibility is maintained, but circuit complexity and power consumption increase
Solution Approach 1:
The patent extracts and eliminates the free list and history file components from the traditional register renaming architecture. By removing these storage elements, the circuit complexity and power consumption are reduced while the core register renaming functionality is preserved through a simplified counter-based allocation mechanism.
Solution Approach 2:
The patent changes the fundamental parameter of register allocation from dynamic list-based management to deterministic counter-based management. This parameter change transforms the system from using complex data structures (free lists, history files) to simple counters that track register allocation states, thereby reducing circuit complexity while maintaining functionality.
2Loss of energy
If traditional free list and history file structures are used, then comprehensive register tracking is achieved, but power consumption increases
Solution Approach 1:
The patent removes the power-consuming free list and history file storage elements from the system. The counter-based approach uses minimal storage (just counter registers) to track allocation states, dramatically reducing power consumption while maintaining sufficient tracking accuracy for deterministic register allocation.
Solution Approach 2:
The patent replaces expensive, complex storage structures (free lists and history files requiring multiple storage elements and access logic) with cheap, simple counter registers. These counters provide the necessary tracking information with minimal hardware resources and lower power consumption.
3Speed
If complex storage elements like free lists are used, then register availability tracking is maintained, but circuit speed decreases
Solution Approach 1:
The patent extracts and removes the complex free list storage structure from the system. By eliminating this complex data structure, the register allocation process becomes faster as it no longer requires searching or managing list entries, instead using direct counter-based availability determination.
Solution Approach 2:
The patent substitutes the mechanical/list-based free list management system with a simpler counter-based system. This substitution replaces complex search and management operations with simple counter increment/decrement operations, significantly improving allocation speed while reducing circuit complexity.
Data Source
AI summary
Register renaming for a deterministically updated register is disclosed. A processor circuit is configured to operate according to an instruction set architecture that defines a plurality of architectural registers. A register file circuit includes a plurality of physical registers having a first subset dedicated for use in renaming a particular architectural register. A first counter value increments in response to execution of an instruction that updates the particular architectural register. A second counter value increments in response to retirement of a previously executed instruction that updated the particular architectural register. The counter values identify respective physical registers. A mapper circuit is configured to determine, in response to an indication that an instruction that updates the particular architectural register, if a physical register is available based on the count values. The physical register to be mapped to the architectural register is selected based on the count value of the first counter.