Fused Load Instruction Execution in Processor Load Store Units
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Solution Overview
Problem
Modern processors face inefficiencies in handling multiple load instructions due to resource sharing and out-of-order execution, leading to delays and reduced processing speed, especially when dealing with consecutive load instructions that require simultaneous execution.
Innovation Solution
The system configures processors to identify fusible load instructions, fuse them into a single instruction, and execute them simultaneously using a load store unit, allowing for concurrent execution and simultaneous write-back to multiple register file entries, thereby optimizing resource utilization and processing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple load instructions are processed separately through standard pipeline stages, then each instruction can be handled individually with proper resource allocation, but processing time increases and execution speed decreases due to sequential handling and resource sharing
Solution Approach 1:
The patent merges multiple fusible load instructions into a single fused load instruction that is issued through one issue queue entry and executed by the load store unit as one operation. This combining eliminates the sequential processing overhead of handling multiple separate instructions while maintaining correct resource allocation and data flow through the pipeline.
2Productivity
If multiple issue queue entries are used for consecutive load instructions, then each instruction can be tracked and executed independently, but resource utilization decreases and processing efficiency is reduced
Solution Approach 1:
Multiple fusible load instructions are merged into a single issue queue entry that contains information about all the original instructions. This single entry is issued through one issue port to the load store unit, reducing the number of queue entries needed while maintaining the ability to track and execute each original instruction's destination correctly.
3Speed
If load instructions are executed sequentially through the execution stage, then resource allocation is simplified, but execution speed decreases due to inability to process multiple instructions simultaneously
Solution Approach 1:
The patent combines multiple fusible load instructions into a single execution operation that retrieves multiple data values from memory in one go. The load store unit executes this fused instruction concurrently, fetching all required data in parallel and then writing back to multiple register file entries simultaneously, thereby achieving both high speed and concurrent execution capability.
4Reliability
If separate write-back operations are performed for each load instruction result, then register file updates are accurate and orderly, but processing time increases and overall performance is reduced
Solution Approach 1:
The patent merges multiple write-back operations into a single combined write-back operation. The load store unit retrieves all required data values from memory in one operation and writes them back to multiple register file entries simultaneously in a single cycle, maintaining accuracy through proper destination tagging while eliminating sequential write-back delays.
Data Source
AI summary
A system, processor, and/or technique configured to: determine whether two or more load instructions are fusible for execution in a load store unit as a fused load instruction; in response to determining that two or more load instructions are fusible, transmit information to process the two or more fusible load instructions into a single entry of an issue queue; issue the information to process the two or more fusible load instructions from the single entry in the issue queue as a fused load instruction to the load store unit using a single issue port of the issue queue, wherein the fused load instruction contains the information to process the two or more fusible load instructions; execute the fused load instruction in the load store unit; and write back data obtained by executing the fused load instruction simultaneously to multiple entries in the register file.