search

riscv / riscv-isa-manual

RISC-V Instruction Set Manual
https://riscv.org/
Creative Commons Attribution 4.0 International
3.7k stars 645 forks source link

Clarify note that compilers may need to change vtype for vmv<nr>r.v #1710

Closed lukel97 closed 2 weeks ago

lukel97 commented 2 weeks ago

In a similar vein to https://github.com/riscvarchive/riscv-v-spec/commit/856fe5bd1cb135c39258e6ca941bf234ae63e1b1, this note states that compilers don't need to "know or change vtype" for whole vector register moves.

There's some truth to this in that compilers can largely ignore SEW and LMUL, but ultimately they do depend on vtype and the current wording might be misleading. A compiler may in fact need to change vtype to clear vill, see: https://github.com/llvm/llvm-project/issues/114518