[CLN-list] Re: optimization and warnings [Was: CLN 1.2.0]

[Joerg Arndt]

Hi,

* Alexei Sheplyakov <varg at theor.jinr.ru> [Jan 21. 2008 12:33]:
> Hello!
> 
> On Sun, Jan 20, 2008 at 12:17:51PM +1100, Joerg Arndt wrote:
> 
> > by default you use
> >  (1) only -O, I suggest to use -O2 (but not -O3).
> 
> I'm not sure if CLN code is safe to compile with plain -O2.

This would be a serios problem IMHO!

> 
> With CXXFLAGS="-m64 -O2 -Wall -march=k8 -finline-limit=2000" I get tons of
> warnings like
> 
> ../../include/cln/number.h: In constructor 'cln::cl_number::cl_number(float)':
> ../../include/cln/number.h:238: warning: type-punning to incomplete type might break strict-aliasing rules
> ../../include/cln/number.h: In member function 'cln::cl_number& cln::cl_number::operator=(float)':
> ../../include/cln/number.h:238: warning: type-punning to incomplete type might break strict-aliasing rules
> ../../include/cln/number.h: In constructor 'cln::cl_number::cl_number(double)':
> ../../include/cln/number.h:239: warning: type-punning to incomplete type might break strict-aliasing rules

Then -no-strict-aliasing should be used!

It seems to me that with strict aliasing and ignoring the warnings
we just proceed "fingers crossed" (?)


> 
> Just for the record, I use
> g++-4.1 (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21).
> 
> >  (2) no warnings!, I suggest to use
> >  -W -Wall -Wconversion -Wsign-promo -Wsign-compare -Wunused \
> >  -Wshadow -Wundef
> 
> -Wall spews a lot of warnings, and signal/noise ratio is quite low for
> this to be useful.

I do that for my stuff all the time:
I consider an warning as a problem and fix it.
When I _know_ there is no problem then I use
a (C-style) cast and comment it.

I found quite a few subtle problems by doing this.


> 
> >   ... and -Werror if you are daring
> 
> Unfortunately, CLN won't compile with -Werror.

Clearly so.

I use -Werror and do a make -k ("keep going"),
then I go through the file where the problems occur.


> 
> Best regards,
> 	Alexei
> 

after all the above is done (a monumental task
with CLN, obviously) valgrind pointed me to a
few _very_ subtle problems which I'd never found
by other other means!

cheers,    jj