[Bug c++/85747] suboptimal code without constexpr

["zamazan4ik at tut dot by" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85747

Alexander Zaitsev <zamazan4ik at tut dot by> changed:

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--- Comment #8 from Alexander Zaitsev <zamazan4ik at tut dot by> ---
(In reply to Marc Glisse from comment #5)
> (In reply to Antony Polukhin from comment #4)
> > Does providing some kind of -Oon-the-fly switch solves the issue with JIT
> > compile times while still allows more optimizations for the traditional non
> > JIT  -O2 builds?
> 
> Not sure what you mean by -Oon-the-fly. If you want to JIT compile the code,
> you more or less need to embed a compiler in the executable...
> 
> The closest I can think of is -fprofile-values. It is possible to collect
> the values of constants during a training run and use them during a second
> compilation. But then knowing more constants in one compilation than the
> other may change the code in ways that the PGO framework will not like.

As I understand Anthony meant here some compiler option which allows to
compiler some "aggresive" mode for detecting code which can be calculated at
compile-time as much as possible, even if it will increase significantly
compilation time. Of course this flag must be disabled by default even with -O3