[Bug tree-optimization/113583] Main loop in 519.lbm not vectorized.

["juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113583

--- Comment #3 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
Ok I see.

If we change NN into 8, then we can vectorize it with load_lanes/store_lanes
with group size = 8:

https://godbolt.org/z/doe9c3hfo

We will use vlseg8e64 which is RVVM1DF[8] == RVVM1x8DFmode.

Here there is report:

/app/example.c:47:21: missed:   no array mode for RVVM1DF[20]
/app/example.c:47:21: missed:   no array mode for RVVM1DF[20]

I believe we enable vec_load_lanes/vec_store_lanes for RVVM1DF[20] which
RVVM1x20DF mode, then we can vectorize it.

But it's not reasonable and not general way to do that. This code require array
size = 20. How about other codes, we may have codes require array size  = 21,
22,..
23, ....etc... The array size can be any number. We can't leverage this
approach
for infinite array size.

So, the idea is that we try to find vec_load_lanes/vec_store_lanes first check
whether it support lanes vectorization for specific array size.

If not, we should be able to lower them into multiple gather/scatter or strided
load/stores.