[Bug tree-optimization/118933] Missed optimization: __builtin_unreachable() does not work as expected on std::vector data compared to raw pointer and length

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118933

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is because `len` is vec.end() - vec.begin() where end is a pointer load.

and then `data + len` gets re-optimized to just vec.end().

And so len is no longer taken into account in std::accumulate loop.