[Bug target/114107] poor vectorization at -O3 when dealing with arrays of different multiplicity, good with -O2

[nathanael.schaeffer at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114107

--- Comment #12 from N Schaeffer <nathanael.schaeffer at gmail dot com> ---
I found the "offending" option, and it seems to be indeed a cost-model problem
as Andrew Pinski said:

good code is generated by:

   gcc -O2 -ftree-vectorize -march=skylake   (since gcc 6.1)
   gcc -O1 -ftree-vectorize -march=skylake   (since gcc 8.1)
   gcc -O3 -fvect-cost-model=very-cheap -march=skylake   (with gcc 13.1+)

bad code is generated otherwise, and in particular:

   gcc -O2 -march=skylake  (does not vectorize)
   gcc -O3 -march=skylake  (bad vectorization with so many permutations)