Accessing local arrays element turned into load form (fp + (index << C1)) +
C2 address.
In the case when access is in the loop we got loop invariant computation.
For some reason, moving out that part cannot be done in
loop-invariant passes.
But we can handle that in target-specific hook (legitimize_address).
That provides an opportunity to rewrite memory access more suitable for the
target architecture.

This patch solves the mentioned case by rewriting mentioned case to ((fp +
C2) + (index << C1))
I have evaluated it on SPEC2017 and got an improvement on leela (over 7b
instructions,
.39% of the dynamic count) and dwarfs the regression for gcc (14m
instructions, .0012%
of the dynamic count).


gcc/ChangeLog:
        * config/riscv/riscv.cc (riscv_legitimize_address): Handle folding.
        (mem_shadd_or_shadd_rtx_p): New predicate.


-- 
With the best regards
Jivan Hakobyan