Physical Register Sharing for Better Register File Utilization

Solution Overview

Problem

Existing processors face inefficiencies due to significant unused storage space in physical registers when using smaller architected registers, limiting the speculative window and potentially slowing down register accesses, despite increasing the size of the physical register file leading to area and power penalties.

Innovation Solution

Implement physical register sharing by partitioning large physical registers to accommodate multiple smaller architected registers, using multi-bit free lists and threshold management to optimize register usage without increasing register file width.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If physical register file width is increased to provide more storage space, then register availability is improved, but area and power consumption increase

Engineering Contradiction:

Improveregister availabilityVSAvoidregister file area

Core Design Contradiction:

Quantity of substanceVSArea of stationary object

Solution Approach 1:

The patent segments physical registers into multiple portions (e.g., first portion and second portion) that can be independently allocated to different architected registers. This allows a single physical register to serve multiple purposes, effectively increasing the number of available registers without increasing the physical register file width or area.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Physical registers are designed to be multi-functional by supporting both larger architected registers and multiple smaller architected registers through portion-based allocation. A single physical register can accommodate different register sizes dynamically, maximizing utilization without requiring additional physical resources.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Quantity of substance

If physical register file width is increased to provide more storage space, then register availability is improved, but power consumption increases

Engineering Contradiction:

Improveregister availabilityVSAvoidregister file power consumption

Core Design Contradiction:

Quantity of substanceVSUse of energy by stationary object

Solution Approach 1:

The patent segments physical registers into multiple portions (e.g., first portion and second portion) that can be independently allocated to different architected registers. This allows a single physical register to serve multiple purposes, effectively increasing the number of available registers without increasing the physical register file width or area.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Physical registers are designed to be multi-functional by supporting both larger architected registers and multiple smaller architected registers through portion-based allocation. A single physical register can accommodate different register sizes dynamically, maximizing utilization without requiring additional physical resources.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If smaller architected registers are used in physical registers, then register utilization efficiency is improved, but unused storage space increases

Engineering Contradiction:

Improveregister utilization efficiencyVSAvoidunused storage space

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The patent segments physical registers into multiple portions (e.g., first portion and second portion) that can be independently allocated to different architected registers. This allows a single physical register to serve multiple purposes, effectively increasing the number of available registers without increasing the physical register file width or area.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of physical registers are allocated to different architected register sizes based on local needs. The system can allocate first portions to larger architected registers and second portions to smaller architected registers, optimizing utilization by matching the specific requirements of each register usage scenario rather than using a uniform allocation strategy.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS12498932B1Physical register sharing

Publication Date: 2025.12.16 APPLE INC

AI summary

Techniques are disclosed relating to physical register sharing. In some embodiments, a processor includes, in a register file, physical registers of a largest architected register size for a given operand type defined in an instruction set architecture (ISA). A register rename circuit of the processor is configured to assign a first physical register to an architected register of the largest architected register size. The register rename circuit is also configured to assign a first portion of a second physical register to a second ISA-defined architected register of a smaller size than the largest architected register size and a second portion of the second physical register to a third ISA-defined architected register of the smaller size. In the second assignment, the second and third architected registers of the smaller size are separate and distinct registers in the ISA.