Register Rename Circuitry Operation Elimination
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Solution Overview
Problem
The limited capacity of instruction queues in data processing apparatuses restricts the flexibility of instruction reordering, as operations must be executed in a specific order and cannot be effectively eliminated without occupying queue space.
Innovation Solution
The implementation of rename circuitry to store mappings between registers with an elimination field value, allowing operations to be replaced with new mappings that reference destination registers, enabling operations to be performed later when the destination register is accessed, thus eliminating the need for these operations to enter the instruction queue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If operations are stored in the instruction queue for execution, then the operations can be executed in order, but the queue capacity is limited and restricts reordering flexibility
Solution Approach 1:
The patent extracts certain operations from the instruction queue by eliminating them entirely. Instead of storing these operations in the queue, the system uses register renaming to directly map source registers to destination registers, removing the need for these operations to occupy queue space while maintaining correct execution semantics
Solution Approach 2:
The patent introduces a new dimension to instruction execution by adding an elimination field to the register renaming structure. This field tracks which operations have been eliminated and when their effects should be applied, moving the operation tracking from the time-based instruction queue to a register-state-based system
2Productivity
If operations are eliminated without occupying queue space, then reordering flexibility increases, but the operation must be performed later when the destination register is accessed
Solution Approach 1:
The patent performs preliminary register renaming and operation elimination during the decode stage, before execution. The elimination field is set in advance, and the actual operation is deferred until the destination register is accessed, at which point the operation is quickly applied without occupying queue space during the critical execution path
Data Source
AI summary
A data processing apparatus is provided. Rename circuitry performs a register rename stage of a pipeline by storing, in storage circuitry, mappings between registers. Each of the mappings is associated with an elimination field value. Operation elimination circuitry replaces an operation that indicates an action is to be performed on data from a source register and stored in a destination register, with a new mapping in the storage circuitry that references the destination register and has the elimination field value set. Operation circuitry responds to a subsequent operation that accesses the destination register when the elimination field value is set; by obtaining contents of the source register, performing the action on the contents to obtain a result, and returning the result.