Re: -pipe passed to gcc via Automake

[Benoit SIGOURE]

On Oct 21, 2007, at 11:24 PM, Bob Friesenhahn wrote:

> On Sun, 21 Oct 2007, Benoit SIGOURE wrote:
>
> > On Oct 21, 2007, at 7:13 PM, NightStrike wrote:
> >
> > > If I wanted -pipe passed in to gcc all the time, do I put that in
> > > AM_CPPFLAGS or AM_CFLAGS?
> >
> > I usually do this in my configure.ac:
> >
> > AC_PROG_CXX
> > # Speed GCC compilation up.
> > if test "$GXX" = yes; then
> >  CXXFLAGS="$CXXFLAGS -pipe"
> > fi
>
> Sounds great, but I have yet to see -pipe actually speed up  
> compilation.  It would only really help if the temporary file  
> directory was remarkably slow or perhaps somehow the user is not  
> allowed to write temporary files.  It is true that GCC's temporary  
> files may be large, but it is also true that pipes only offer  
> limited buffering and two programs must execute at once (requiring  
> context switching) rather than just one at a time.
>
> Sometimes pipes may not be supported.  In that case hopefully GCC  
> simply ignores the request rather than refusing to run.

Hmm indeed, I tested a `make clean all' (with ccache disabled and  
all) on a project with ~18k lines of code (sloccount) and the build  
without `-pipe' was 6s "faster".  So yeah, I doubt that -pipe speeds  
anything up.

Thanks!

--
Benoit Sigoure aka Tsuna
EPITA Research and Development Laboratory

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