Algorithms for Improving the Automatically Synthesized Instruction Set of an Extensible Processor
Abstract
This paper introduces novel algorithms designed to optimize the automatically synthesized instruction sets (ISAs) used in extensible processors and hardware accelerators like RISC-V. The methods include a Common Operations Clustering algorithm to reduce compiled code size and a Subsuming Functions algorithm to identify and eliminate redundant specialized instructions. Experimental results across cryptography and 3D graphics benchmarks demonstrate significant efficiency gains, achieving up to 10% reduction in compiled code size and reducing the ISA extension size by up to 2.5 times.
Report
Algorithms for Improving the Automatically Synthesized Instruction Set of an Extensible Processor
Key Highlights
- Focus on Extensibility: The research addresses the challenge of designing specialized instructions for extensible processor architectures (e.g., RISC-V) used as programmable hardware accelerators.
- Two Core Algorithms: Two novel algorithms are introduced to improve the quality of automatically synthesized ISAs: Common Operations Clustering and Subsuming Functions.
- Code Size Reduction: The Common Operations Clustering algorithm successfully reduced the size of the compiled code by 9% (Magma cipher) and 10% (AES cipher) by efficiently recomputing common intermediate operations.
- ISA Reduction: The Subsuming Functions algorithm, which identifies and removes redundant instructions, drastically reduced the synthesized instruction set extension size by 2 times (Magma) and 2.5 times (AES).
- Practical Validation: The methods were validated across crucial domains: cryptography (Magma and AES) and 3D graphics (Volume Ray-Casting).
Technical Details
| Feature | Description / Specifics |
|---|---|
| Target Systems | Extensible processors and programmable hardware accelerators, relevant to architectures like RISC-V. |
| Common Operations Clustering (COC) | An algorithm that improves synthesized ISAs by clustering common operations whose result is consumed by multiple subsequent operations, thereby enabling their efficient recomputation within the synthesized instruction. |
| Subsuming Functions (SF) Algorithm | A method used post-synthesis to identify redundant specialized instructions—those that possess functional equivalents among the remaining synthesized instructions—to minimize the extension size. |
| Results: Cryptography (AES/Magma) | COC reduced code size (9-10%); SF reduced instruction set extension size (2x to 2.5x). |
| Results: 3D Graphics (Volume Ray-Casting) | The use of SF reduced the problem-specific instruction extension set size from 5 instructions down to only 2, without loss of functionality. |
Implications
This research significantly advances the field of automatic instruction set synthesis, which is particularly relevant to the burgeoning RISC-V ecosystem:
- Enhanced Customization Efficiency: By automating the optimization of generated specialized instructions, hardware architects can create more efficient accelerators without requiring exhaustive manual tuning, lowering development time and costs.
- Improved Hardware Utilization: Reducing the size and complexity of the ISA extension (as demonstrated by the 2x to 2.5x reductions) leads directly to smaller, less power-hungry, and easier-to-implement hardware accelerators.
- Compiler Optimization: The Common Operations Clustering technique results in smaller compiled code size, improving memory footprint and instruction cache performance for highly accelerated applications.
- Accelerating Key Domains: The proven efficiency improvements in cryptographic and 3D graphics workloads ensure that RISC-V platforms customized using these algorithms will be highly competitive in specialized high-performance computing tasks.
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