Register Last Use Detection for Decode-Time Instruction Optimization
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Solution Overview
Problem
Current processor technologies face inefficiencies in decoding and executing multiple threads due to hardware costs and resource interference, leading to potential performance degradation and increased complexity in managing thread-level parallelism.
Innovation Solution
The implementation of an out-of-order processor with an intermediate register mapper allows for the efficient management of physical registers by moving logical-to-physical register renaming data from a unified main mapper to an intermediate register mapper before completion, freeing up mapper entries for reuse and optimizing instruction execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multithreading is implemented to improve system throughput, then overall execution speed is improved, but hardware complexity and resource interference increase
Solution Approach 1:
The patent segments the register file into multiple banks (e.g., even and odd numbered banks) that can be independently accessed by different threads. This allows simultaneous register operations for multiple threads without requiring complete register file duplication, thereby improving throughput while controlling hardware complexity growth.
Solution Approach 2:
The patent introduces a thread identifier dimension to the register access mechanism, allowing the same physical register file to serve multiple threads by selecting appropriate banks based on thread ID. This dimensional addition enables multithreading support without proportionally increasing hardware resources.
2Productivity
If register renaming is used to improve instruction level parallelism, then instruction throughput is improved, but mapper entry availability decreases
Solution Approach 1:
The patent enables earlier recovery of mapper entries by detecting when a renamed register's value is no longer needed (last use detection). Once identified, the mapper entry can be freed for reuse before the instruction actually completes, increasing mapper entry availability while maintaining instruction throughput.
Solution Approach 2:
The patent performs preliminary detection of last-use registers during the decode stage, before instruction execution completes. This allows mapper entries to be freed in advance, increasing availability for subsequent renaming operations without impacting current instruction throughput.
3Adaptability or versatility
If thread switching hardware is added to improve multithreading capability, then thread execution is improved, but execution frequency decreases
Solution Approach 1:
The patent merges thread management capabilities into the existing register file structure by introducing bank selection based on thread identifiers. This integration approach enables multithreading without adding separate, bulky thread switching hardware, thereby preserving execution frequency while improving multithreading capability.
4Speed
If complete register sets are replicated for each thread to improve switching speed, then context switching is improved, but hardware cost increases
Solution Approach 1:
The patent segments the register file into multiple banks that can be associated with different threads. Instead of replicating complete register sets, each bank contains a portion of registers that can be rapidly switched between threads, achieving fast context switching with reduced hardware cost compared to full replication.
Data Source
AI summary
Two computer machine instructions are fetched for execution, but replaced by a single optimized instruction to be executed, wherein a temporary register used by the two instructions is identified as a last-use register, where a last-use register has a value that is not to be accessed by later instructions, whereby the two computer machine instructions are replaced by a single optimized internal instruction for execution, the single optimized instruction not including the last-use register.