Patch: automatic dependencies for gcc

[Ralf Wildenhues]

* Tom Tromey wrote on Sun, Mar 09, 2008 at 04:09:53PM CET:
> >>>>> "Ralf" == Ralf Wildenhues <Ralf.Wildenhues@gmx.de> writes:
> 
> Ralf> The reason I see against my proposal that IMVHO carries real weight
> Ralf> would be if you were to require up to date deps files.  I would not know
> Ralf> how to easily reformulate
> Ralf>   %.o $(DEPDIR)/%.d: %.c
> Ralf> rules into the subdir/$(DEPDIR) scheme.  Why aren't you using this BTW?
> Ralf> It would already be a bit safer than what you currently have, even if
> Ralf> you don't go all the way and make $(DEPFILES) a prerequisite of 'all'.
> 
> It seems to me that this will cause us to run these rules at -include
> time.  -include will not error if the file does not exist, but if the
> file can be remade, make will try to do that.

I don't think make will ignore prerequisites of the .c files when
considering remaking include files.  If it did, I'd consider that
a bug.  Or does gcc/Makefile.in not have full dependency information?

> I think include time is too early to build the .d files.

Sure.  But I think make would just remake them after redoing whatever
else it needs to redo.  But maybe I have also misunderstood you.

Cheers,
Ralf