[Bug target/115336] [15] rv64gcv_zvl256b miscompile at -O3

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115336

--- Comment #2 from Robin Dapp <rdapp at gcc dot gnu.org> ---
It looks to me as if we're expecting the result of a gather_load to be zero
when it's masked out (semantics of mask_gather_load) but for
mask_len_gather_load we actually describe it as undefined.  Here the mask is
all zeros and we OR the result with 1.  Because of stale values this doesn't
result in 1 but rather garbage.  Maybe our mask representation also plays a
part but I'm pretty sure zeroing the result before the gather would help.