Re: Faster compilation speed

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

Noel Yap wrote:-

> I stand corrected.  (I'm assuming gcc doesn't do this
> in cases where the header guard might have side
> effects or if there's a matching #else for the
> #ifndef).

Correct.  Header guards with side effects hardly exist
I think.  We recognize #ifndef and #if !defined with
optional parentheses.  Comments and whitespace do not
affect the optimization.  Headers with #else, #elif
at the top level, and with anything outside the guards,
or with a header guard that comes from a macro expansion
are not optimized this way.

> Do you think precompiled headers would help build
> speed across several compiles since it would be
> another source to eliminate repeated file opens?

I don't think repeated file opens are high on the list
of time eaters, particularly because of the optimization
I mentioned.  Tokenization and parsing probably take
much longer.

Neil.