[Bug tree-optimization/87465] [8/9 Regression] Loop removal regression

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87465

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org
   Target Milestone|---                         |9.0
            Summary|Loop removal regression     |[8/9 Regression] Loop
                   |                            |removal regression

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This changed with r255267, we don't peel/completely unroll the loop nest
anymore.

I'd say in this case it would be best done by a constexpr-like evaluation pass,
where we'd just at compile time try to evaluate a few (hundreds) iterations of
the loop at compile time and see if we can simply capture the whole outcome of
the loop (final values, maybe some simple array stores).
Until then, use C++14 constexpr evaluation if you want stuff to be evaluated at
compile time.