Register Alias Table for Operand Storage Bottleneck
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Solution Overview
Problem
In complex data processing systems, the increased complexity and number of operations per clock cycle lead to performance bottlenecks due to insufficient read ports in register files, requiring significant storage and complexity in issue circuitry to manage source operands for pending operations.
Innovation Solution
The implementation of value analysis circuitry to determine if a reduced size representation of a data value can be stored in a source identifier field, allowing the replacement of register identifiers with reduced size representations, thereby reducing the need for register file access when issuing operations to execution circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the system allows multiple operations to be dispatched to execution circuitry in a particular clock cycle, then productivity is improved, but device complexity increases due to significant complexity in the construction of the register file to provide sufficient read ports
Solution Approach 1:
The patent extracts the data value storage from the register file by implementing a register alias table that stores reduced-size representations of data values. This separates the identification function (register alias table) from the storage function (register file), allowing multiple read ports to be effectively provided through the alias table without increasing register file complexity.
Solution Approach 2:
The patent introduces a new dimension by adding the register alias table as an intermediate layer between the issue circuitry and the register file. This alias table operates in a different dimension (reduced-size representations) compared to the full-width register file, enabling parallel access without increasing the register file's read port count.
2Ease of operation
If data values are retrieved from the register file and stored within the record structure maintained by issue circuitry prior to issuance, then ease of operation is improved, but device complexity increases significantly due to increased storage requirements and complexity of issue circuitry
Solution Approach 1:
The patent creates a simplified copy of data values in the register alias table using reduced-size representations (such as immediate values or compressed encodings). This copy contains sufficient information to reconstruct or directly provide the source operands, eliminating the need to store full data values in the issue circuitry while maintaining ease of operand retrieval.
Solution Approach 2:
The patent changes the parameter of data representation from full-width data values to reduced-size representations in the register alias table. This parameter change enables the alias table to store multiple representations efficiently, simplifying the issue circuitry's storage requirements while maintaining operational ease.
3Reliability
If full-size data values are stored in source identifier fields, then reliability is improved by ensuring complete data availability, but device complexity increases due to insufficient field size to accommodate both register identifiers and data values
Solution Approach 1:
The patent segments the source operand identification into two parts: the register alias table stores reduced-size data value representations, while the issue circuitry maintains references to these aliases. This segmentation allows the source identifier fields to remain compact while reliability is maintained through the alias mechanism that ensures complete data availability when needed.
Data Source
AI summary
An apparatus and method are provided for storing source operands for operations. The apparatus comprises execution circuitry for performing operations on data values, and a register file comprising a plurality of registers to store the data values operated on by the execution circuitry. Issue circuitry is also provided that has a pending operations storage identifying pending operations awaiting performance by the execution circuitry and selection circuitry to select pending operations from the pending operation storage to issue to the execution circuitry. The pending operations storage comprises an entry for each pending operation, each entry storing attribute information identifying the operation to be performed, where that attribute information includes a source identifier field for each source operand of the pending operation. The source identifier field has a field size sufficient to enable a register identifier to be stored within the source identifier field to identify the register used to store the data value forming the source operand. However, the field size is insufficient to store the data value as stored in the register. Value analysis circuitry is responsive to the execution circuitry generating a data value that will be used as a source operand for a pending operation, to determine whether a reduced size representation of that generated data value can be accommodated within the associated source identifier field of the entry for that pending operation. If so, the reduced size representation is generated and a control signal is issued to the issue circuitry to cause the register identifier for that source operand to be replaced by the reduced size representation of the data value. By such an approach, it is possible to increase the performance of the apparatus and/or to simplify the construction of the register file.