[Bug ipa/101279] Function attributes often block inlining

[david at westcontrol dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101279

--- Comment #5 from David Brown <david at westcontrol dot com> ---
(In reply to Richard Biener from comment #4)
> (In reply to frankhb1989 from comment #3)
> > There is a more specific instance here: can_inline_edge_by_limits_p in
> > ipa-inline.cc treats flags and "optimize" attributes differently.
> 
> A bit up there's a blacklist we maintain where inlining is not OK because it
> results in semantic differences.
> 
> Generally we it's hard to second-guess the users intention when looking
> at an inline edge with different optimization settings of caller and callee.
> For C++ comdats there might be even multiple variants with different
> optimization level (but we only keep one, special-casing this a bit).

I appreciate the "err on the side of caution" attitude.  Perhaps there could be
an extra "I know what I'm doing" attribute that lets you override the
blacklisting in a particular case.  This would only really make sense in cases
where the attribute can be attached to the expressions and statements within
the function (I think "-fwrapv" would be in this category).  In cases where
this is not possible, an error or warning message would be in order as the
compiler can't do what the programmer is asking.