Building C++ with --enable-languages=c,fortran

Building C++ with --enable-languages=c,fortran

[Thomas Koenig]

Hello world,

I just noticed that C++ now appears to be built by default, even when 
only the C and fortran are specified.  The configure line


../trunk/configure  --prefix=$HOME --enable-languages=c,fortran 
--with-mpc=/usr/local --with-mpfr=/usr/local

leads to the message

checking for version 0.11 (revision 0 or later) of PPL... no 

The following languages will be built: c,c++,fortran,lto

I see recent changes by Ian in this area, but nothing in the ChangeLog
suggests to me that this was intentional.

Any ideas?

Re: Building C++ with --enable-languages=c,fortran

[Steve Kargl]

On Sat, Aug 06, 2011 at 12:52:02AM +0200, Thomas Koenig wrote:
> Hello world,
> 
> I just noticed that C++ now appears to be built by default, even when 
> only the C and fortran are specified.  The configure line
> 
> 
> ../trunk/configure  --prefix=$HOME --enable-languages=c,fortran 
> --with-mpc=/usr/local --with-mpfr=/usr/local
> 
> leads to the message
> 
> checking for version 0.11 (revision 0 or later) of PPL... no 
> 
> The following languages will be built: c,c++,fortran,lto
> 
> I see recent changes by Ian in this area, but nothing in the ChangeLog
> suggests to me that this was intentional.
> 
> Any ideas?

It appears the original thread starts here 

http://gcc.gnu.org/ml/gcc-patches/2011-07/msg01304.html



-- 
Steve

Re: Building C++ with --enable-languages=c,fortran

[Ian Lance Taylor]

Thomas Koenig <tkoenig@netcologne.de> writes:

> I just noticed that C++ now appears to be built by default, even when
> only the C and fortran are specified.  The configure line
>
>
> ../trunk/configure  --prefix=$HOME --enable-languages=c,fortran
> --with-mpc=/usr/local --with-mpfr=/usr/local
>
> leads to the message
>
> checking for version 0.11 (revision 0 or later) of PPL... no 
>
> The following languages will be built: c,c++,fortran,lto
>
> I see recent changes by Ian in this area, but nothing in the ChangeLog
> suggests to me that this was intentional.

It is intentional.  In current mainline stages 2 and 3 are now by
default built with the C++ compiler, not the C compiler.  Therefore, the
C++ compiler must be built in stages 1 and 2, in order to use to build
the stages 2 and 3 compiler.  And then of course we build the C++
compiler in stage 3 in order to compare it.

The ChangeLog entry says that if --enable-build-poststage1-with-cxx is
set, C++ becomes a boot language.  That is what you are seeing.  I guess
what the ChangeLog entry does not say is that
--enable-build-poststage1-with-cxx is set by default.

Ian

Re: Building C++ with --enable-languages=c,fortran

[Steve Kargl]

On Fri, Aug 05, 2011 at 06:51:12PM -0700, Ian Lance Taylor wrote:
> Thomas Koenig <tkoenig@netcologne.de> writes:
> 
> > I just noticed that C++ now appears to be built by default, even when
> > only the C and fortran are specified.  The configure line
> >
> >
> > ../trunk/configure  --prefix=$HOME --enable-languages=c,fortran
> > --with-mpc=/usr/local --with-mpfr=/usr/local
> >
> > leads to the message
> >
> > checking for version 0.11 (revision 0 or later) of PPL... no 
> >
> > The following languages will be built: c,c++,fortran,lto
> >
> > I see recent changes by Ian in this area, but nothing in the ChangeLog
> > suggests to me that this was intentional.
> 
> It is intentional.  In current mainline stages 2 and 3 are now by
> default built with the C++ compiler, not the C compiler.  Therefore, the
> C++ compiler must be built in stages 1 and 2, in order to use to build
> the stages 2 and 3 compiler.  And then of course we build the C++
> compiler in stage 3 in order to compare it.
> 
> The ChangeLog entry says that if --enable-build-poststage1-with-cxx is
> set, C++ becomes a boot language.  That is what you are seeing.  I guess
> what the ChangeLog entry does not say is that
> --enable-build-poststage1-with-cxx is set by default.
> 

What are the additional resource requirements?  Some of
us have old hardware and limited $.

-- 
Steve

Re: Building C++ with --enable-languages=c,fortran

[Ian Lance Taylor]

Steve Kargl <sgk@troutmask.apl.washington.edu> writes:

>> The ChangeLog entry says that if --enable-build-poststage1-with-cxx is
>> set, C++ becomes a boot language.  That is what you are seeing.  I guess
>> what the ChangeLog entry does not say is that
>> --enable-build-poststage1-with-cxx is set by default.
>> 
>
> What are the additional resource requirements?  Some of
> us have old hardware and limited $.

The main additional resource requirement is building libstdc++ in stage
1 (and stages 2 and 3 if you were previously not building the C++
compiler at all).  The C++ compiler proper is fairly small by
comparison.

At present you can use --disable-build-poststage1-with-cxx.  However, in
the future, I would like to change gcc to always build with C++.  Yes,
this will take more resources.

Ian

Re: Building C++ with --enable-languages=c,fortran

[Mikael Morin]

On Saturday 06 August 2011 00:52:02 Thomas Koenig wrote:
> Hello world,
> 
> I just noticed that C++ now appears to be built by default, even when
> only the C and fortran are specified.
Yes, but it doesn't make much difference in practice. The only difference I 
saw is the debugging symbols including the full prototype (not only the 
function name) in the debugger.
WRT to bootstrap time, as usual: it's too long.

Mikael

Re: Building C++ with --enable-languages=c,fortran

[Toon Moene]

On 08/06/2011 11:22 AM, Mikael Morin wrote:

> WRT to bootstrap time, as usual: it's too long.

Well, that all depends on your (time) frame of reference, of course.  In 
the summer months leading up to Craig Burley asking for volunteers 
testing g77 (the g77-alpha phase), i.e., during the summer of 1992, a 
bootstrap of GCC (C and C++) took 8 hours on my single 25 Mhz Motorola 
68040 powered Next Station.

With the new gcc, I could build a fresh f2c in minutes, and, using that 
combo (f2c+gcc) a recompile of our weather forecasting code took another 
10 minutes.

Nowadays, on a *4 year old* quad core Core 2 machine, building C, C++, 
Ada and Fortran takes less than 2 hours, so given that I put in 4 times 
as many processors, the rest of the hardware keeps up with providing me 
a bootstrap in 1/4th of the time it took 19 years ago, giving me twice 
the number of front ends plus run time libraries.

I think the outlook is good :-)

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
At home: http://moene.org/~toon/; weather: http://moene.org/~hirlam/
Progress of GNU Fortran: http://gcc.gnu.org/wiki/GFortran#news

Re: Building C++ with --enable-languages=c,fortran

[Steve Kargl]

On Sat, Aug 06, 2011 at 03:16:43PM +0200, Toon Moene wrote:
> On 08/06/2011 11:22 AM, Mikael Morin wrote:
> 
> >WRT to bootstrap time, as usual: it's too long.
> 
> Well, that all depends on your (time) frame of reference, of course.  In 
> the summer months leading up to Craig Burley asking for volunteers 
> testing g77 (the g77-alpha phase), i.e., during the summer of 1992, a 
> bootstrap of GCC (C and C++) took 8 hours on my single 25 Mhz Motorola 
> 68040 powered Next Station.
> 
> With the new gcc, I could build a fresh f2c in minutes, and, using that 
> combo (f2c+gcc) a recompile of our weather forecasting code took another 
> 10 minutes.
> 
> Nowadays, on a *4 year old* quad core Core 2 machine, building C, C++, 
> Ada and Fortran takes less than 2 hours, so given that I put in 4 times 
> as many processors, the rest of the hardware keeps up with providing me 
> a bootstrap in 1/4th of the time it took 19 years ago, giving me twice 
> the number of front ends plus run time libraries.
> 
> I think the outlook is good :-)
> 

You left out the crucial hardware spec.  How much memory
did you have 19 years ago compared to the system today?
My experience with g++ is that it will consume more memory
than gcc.  

-- 
Steve

Re: Building C++ with --enable-languages=c,fortran

[Toon Moene]

On 08/06/2011 05:14 PM, Steve Kargl wrote:

> You left out the crucial hardware spec.  How much memory
> did you have 19 years ago compared to the system today?
> My experience with g++ is that it will consume more memory
> than gcc.

That might be true - I have never experienced memory shortage *building* 
C and C++ in 1992 - I had 16 Mbyte of RAM at that time.

Nowadays I have 4 Gbyte of RAM, but still *bootstrapping* doesn't seem 
to be a problem (certain parts of the weather forecasting system these 
days stretch the virtual memory system, but with 4 Gbyte RAM and 11 
Gbyte SWAP I still survive).

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
At home: http://moene.org/~toon/; weather: http://moene.org/~hirlam/
Progress of GNU Fortran: http://gcc.gnu.org/wiki/GFortran#news