[clang] [llvm] [RISCV][VLS] Support RISCV VLS calling convention (PR #100346)

[Brandon Wu via llvm-commits]

4vtomat wrote:

Update:
1. Handle struct of fixed-length vectors
2. Remove `-mriscv-abi-vlen=N` option

https://github.com/llvm/llvm-project/pull/100346