Speeding up config.status

[Tom Tromey]

Lately I've been thinking about speeding up config.status, especially
as regards automake.

Right now each Makefile.in automake generates has *every* configure
substitution in it.  Why do all this work?  For automake it would be
better if config.status simply created a file with all the
substitutions, like so: "FOO = @FOO@".  Then we could include this
file from Makefile (either by copying or by reference).

Ok, one problem is that there can be configure substitutions other
than simple assignments in Makefile.in.  But automake could rewrite
@FOO@ to $(FOO) automatically.

The other objection is that automake conditionals require configure
substitutions.  I think it would be reasonable to investigate
including support for conditionals directly into autoconf and
config.status.  I imagine we could find some faster implementation
than the current one.  For instance, we could preprocess Makefile.in
using awk.

I know config.status is faster in 2.5x.  But this would make things
faster still, at least for projects with more than one directory that
use automake.

Tom