Re: Faster compilation speed

[Neil Booth <neil at daikokuya dot co dot uk>]

Noel Yap wrote:-

> At first, I think all that's really needed is a cpp
> option, say --preprocess-includes, that just goes
> through and preprocesses the #include directives (eg
> it doesn't preprocess #define's, #if's, ...).

Heh, if only life were this easy.  If you actually think about what CPP
does, you'd realize this is a no-go.  Two immediate issues:

1) #include can take a macro as argument
2) #include can appear in preprocessor conditional blocks.  You
   only know whether they are processed if you know the correct value
   of the #if.  This often depends on macro expansions, and correct
   processing of prior includes.  Of course, #defines appear in
   conditional blocks too, so this is kind of important to get right.

There are no easy shortcuts here: to preprocess something properly,
you have to do *everything* the preprocessor does "normally".  There
are no shortcuts, not even trivial ones.

We *do* do too many stats and opens though; when I get time I'll post
my ideas about this.

Neil.