Any way to get rid of -MP parameter to gcc for dependency creation?

[Xan Lopez]

Hi,

First a bit of context: for the GTK+ port of WebKit
(www.webkitgtk.org) we are using autotools as our build system
(autoconf+automake+libtool, the whole lot). We have a *lot* of files,
so the resulting Makefile is about 9MB in size and takes, in my
system, about 55s to go through a null-build (that is, just typing
'make' when there's nothing to do).

Today I was looking at ways of reducing this, and I managed to save
10s by getting rid of some implicit rules we don't need (the win is
essentially the same than using -r in Make). After that I found that
for each target in the build a .Plo file with the dependencies is
generated, and that an empty rule for each dependency of that target
is added to that file. This adds up *really* quickly in size, and I
found that by removing all those I can go from ~43s (the time without
the implicit rules) to ~20s. I realize this has some uses (as the -MP
doc explains), but 23 seconds per build seems excessive, so I think we
can try to live without it. Problem is, apparently it's totally
hardcoded in am/depend2.am, so: any idea on how to get rid of it in
some kind of prost-processing step? (Even grepping/replacing the whole
Makefile after is generated will very likely take a fraction of those
23s).

Alternatively, is there some well-known way to reduce either the size
or the processing time for the Makefile in huge automake projects?[1]

Cheers,

Xan

[1]: I found this thread,
http://lists.gnu.org/archive/html/automake/2003-12/msg00103.html, from
years ago, but I'm not sure there was any definitive conclusion, and
gcj nowadays seems different than how the mail implies it was back
then.