Prototyping custom RISC-V instructions with Seal5 and CoreDSL

Seal5 provides the efficient transformation of custom RISC-V instructions defined in CoreDSL into the LLVM toolchain and the ETISS instruction set simulator. This paper evaluates this approach by implementing an extension for the ChaCha20 cipher, achieving a substantial performance improvement in the test case without any change to its source code and a tiny increase in core size. The results demonstrate the potential of this approach for rapid exploration of customising a RISC-V-based product through extension instructions.