Re: [Boost-users] [signals2][variant] inline warning with MSVC 2022

From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2022-09-23 08:25:45

Am 23.09.22 um 09:18 schrieb Andrey Semashev via Boost:
> Maybe we could use __pragma in BOOST_FORCEINLINE on a recent enough MSVC?
>
> https://godbolt.org/z/oh5szGd4r
This is an awesome idea and I'm surprised it actually works.

I wanted to propose a PR to Boost.Config which adds your code to the 
test suite making sure it compiles warning-free.

However it fails on GCC:

 > error: inlining failed in call to ‘always_inline’ ‘unsigned int 
f_not_inlined(unsigned int)’: function not considered for inlining
 >Â  Â  19 | BOOST_FORCEINLINE unsigned f_not_inlined( unsigned x )
 >Â  Â Â Â Â  |Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  ^~~~~~~~~~~~~
 > note: called from here
 >Â  Â  21 |Â Â Â Â  return x == 0 ? 0: x * f_not_inlined( x-1 );

So I'm actually not sure how we want to define the behavior of 
BOOST_FORCEINLINE especially as it is a macro officially available for 
users too.

Given the name a warning is appropriate especially given that other 
compilers error in such cases.
For the GCC behavior I found 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63220 which cites

 > always_inline is _not_ an optimization hint! always_inline was meant 
to mark functions that won't work correctly if not inlined.

So I'd say we need a `BOOST_INLINE` macro expanding to a (strong) 
inlining hint and does not generate errors/warnings.
And Boost libraries should most likely use that, not the FORCEINLINE macro.