RE: how to include dependencies only if includes changed

[Mark Galeck (CW)]

> See http://make.paulandlesley.org/autodep.html for a good way to handle auto 
> dependencies in make. Using the methods described in the article, you will 
> only build dependencies when they are needed.

Oh yes, Pete, I am very much aware of this article.  In fact, I combined ideas 
from that article, with the auto-dep section from GNU make manual, to implement 
the auto-dependencies.  The problem is, and I believe neither that article nor 
make manual address it, is that I don't want to "-include" all the dependencies 
unless necessary.  This is because I am dealing with a code base of over 8 
million lines, more than 1000 .c files, each depending on around 500 .h files.  
The dependencies, all of them, take about 1 minute to "-include", even if you 
are just rebuilding one .o file.  It is OK with me, but other developers would 
not be happy about it.  

I did finally come up with some solution, let me write it here, maybe someone 
can comment if there is a better way.  The target chooseIncl, is OS dependent:  
it decides whether any included files have changed since last time, and based 
on that invokes
$(MAKE) incl 
or
$(MAKE) noIncl

--------------------
Main makefile (relevant fragments)
------------------------
-include included

.PHONY: all incl noIncl
all: mainProgram
incl noIncl: all

#goals that do not need any .d makefiles
GOALS_REQ_NO_INCLUDE = noIncl lastIncl clean

#goals that require some .d makefiles
GOALS_REQ_INCLUDE = $(filter-out $(GOALS_REQ_NO_INCLUDE), $(MAKECMDGOALS))

#goals that require all .d makefiles
GOALS_REQ_ALL_INCLUDE = $(filter-out %.o, $( GOALS_REQ_INCLUDE))

ifneq (, $( GOALS_REQ_ALL_INCLUDE))
-include $(OBJECTS:.o=.d) 
else
-include $(GOALS_REQ_INCLUDE:.o=.d)
Endif

--------------------------------
"included" makefile,generated automatically by a Perl script when mainProgram 
is rebuilt (relevant fragments)
-------------------------------
chooseIncl:
        ($(MAKE) -q lastIncl && ( $(MAKE) noIncl & touch lastIncl)) || ($(MAKE) 
incl & touch lastIncl)

lastIncl:\
foobar.h\
foobar1.h\
(... all the header files)