[Bug target/121959] riscv: vector sign extend instead of zero extend

[rdapp at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121959

--- Comment #9 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Pan's patch is upstream which solves this at RTL level.  I detailed what would
need to be done for a gimple-level solution in my reply to his patch:

https://gcc.gnu.org/pipermail/gcc-patches/2025-November/699790.html