Re: Checking dependency style

[Ralf Wildenhues]

Hello Rohit,

* Rohit Arul Raj wrote on Tue, Oct 17, 2006 at 09:04:32AM CEST:
> 
> I was trying to build a package (m4 1.4.7) using two different cross
> compilers. one was GCC 4.1.1and other was non GNU compiler 3.4. My
> autoconf version is  2.6.0, automake is 1.9.6
> 
> one of the output of the configure was checking dependecy style. it
> gave gcc3 as result while building with GCC crosscompiler. while
> building with the non GNU compiler it gave 'none'.

Which compiler is "the other one"?

> 1.Why do we check or under what condition do we have to check dependecy 
> style?

The check comes from Automake, not Autoconf.  The makefiles generated by
Automake normally include dependency tracking, unless told otherwise.
The configure script does some tests for some dependency generation
methods it knows about and tells you the result.  You can use
  ./configure --disable-dependency-tracking

to disable it.  By default, dependency tracking will only be enabled for
generation methods that operate as side-effects to compilation, i.e.,
that do not require a separate tool like 'makedepend' to run.  If you
are desperate to getting dependencies even in that case (a couple of
other methods are possible too), use
  ./configure --enable-dependency-tracking

> 2. Will it affect the performance of the compiler?

Well.  The gcc3 depmode is very fast, it's overhead is almost
negligible, from all I know.  All other methods require at least the
running of the 'depcomp' script, which may call 'sed' a couple of times.
Not a too big overhead though, if you ask me.  The slow methods (which
you explicitly have to enable) may have an overhead you can actually
notice (i.e., more than a few percent).  All guesswork here.

> 3. What are other dependency checks available other than gcc3?

Take a look at the depcomp script that comes from Automake and should be
installed as part of the package you're compiling.  Its contents define
what methods it knows.

Hope that helps.

Cheers,
Ralf