[Bug tree-optimization/84712] Missed evaluating to constant at tree level

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84712

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
We unroll quite late (cunroll) and there aren't any passes (like FRE) after
that to do the propagation. Adding #pragma GCC unroll 16 before the loop lets
it optimize.