Efficient Implementation of RISC-V Vector Permutation Instructions
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arXiv
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| Auteurs principaux: | , , , |
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| Format: | Preprint |
| Publié: |
2025
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| _version_ | 1866916768557039616 |
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| author | Titopoulos, Vasileios Alexakis, George Nicopoulos, Chrysostomos Dimitrakopoulos, Giorgos |
| author_facet | Titopoulos, Vasileios Alexakis, George Nicopoulos, Chrysostomos Dimitrakopoulos, Giorgos |
| contents | RISC-V CPUs leverage the RVV (RISC-V Vector) extension to accelerate data-parallel workloads. In addition to arithmetic operations, RVV includes powerful permutation instructions that enable flexible element rearrangement within vector registers --critical for optimizing performance in tasks such as matrix operations and cryptographic computations. However, the diverse control mechanisms of these instructions complicate their execution within a unified datapath while maintaining the fixed-latency requirement of cryptographic accelerators. To address this, we propose a unified microarchitecture capable of executing all RVV permutation instructions efficiently, regardless of their control information structure. This approach minimizes area and hardware costs while ensuring single-cycle execution for short vector machines (up to 256 bits) and enabling efficient pipelining for longer vectors. The proposed design is integrated into an open-source RISC-V vector processor and implemented at 7 nm using the OpenRoad physical synthesis flow. Experimental results validate the efficiency of our unified vector permutation unit, demonstrating that it only incurs 1.5% area overhead to the total vector processor. Furthermore, this area overhead decreases to near-0% as the minimum supported element width for vector permutations increases. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_07112 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Efficient Implementation of RISC-V Vector Permutation Instructions Titopoulos, Vasileios Alexakis, George Nicopoulos, Chrysostomos Dimitrakopoulos, Giorgos Hardware Architecture RISC-V CPUs leverage the RVV (RISC-V Vector) extension to accelerate data-parallel workloads. In addition to arithmetic operations, RVV includes powerful permutation instructions that enable flexible element rearrangement within vector registers --critical for optimizing performance in tasks such as matrix operations and cryptographic computations. However, the diverse control mechanisms of these instructions complicate their execution within a unified datapath while maintaining the fixed-latency requirement of cryptographic accelerators. To address this, we propose a unified microarchitecture capable of executing all RVV permutation instructions efficiently, regardless of their control information structure. This approach minimizes area and hardware costs while ensuring single-cycle execution for short vector machines (up to 256 bits) and enabling efficient pipelining for longer vectors. The proposed design is integrated into an open-source RISC-V vector processor and implemented at 7 nm using the OpenRoad physical synthesis flow. Experimental results validate the efficiency of our unified vector permutation unit, demonstrating that it only incurs 1.5% area overhead to the total vector processor. Furthermore, this area overhead decreases to near-0% as the minimum supported element width for vector permutations increases. |
| title | Efficient Implementation of RISC-V Vector Permutation Instructions |
| topic | Hardware Architecture |
| url | https://arxiv.org/abs/2505.07112 |