Re: Suggestions for improving gcc 3.2 compilation speed?

[Mike Stump <mrs at apple dot com>]

On Friday, March 7, 2003, at 11:12 AM, Benjamin Kosnik wrote:
> > I have a g++ compiler that is 5.6x faster than the current g++ when
> > compiling large C++ code bases. That's when compared to a g++ PCH,
> > without it, more like 8x to 16x faster when PCH isn't used.
>
> Your PCH numbers are interesting to me.
>
> I cannot get PCH to work with g++. How are you able to do this? Are you
> generating individual .pch files for each header (don't see any
> significant speed improvement), or are you using -include
> big_globbed_header.h.pch (and if so, can you port the patches to do 
> this
> to mainline g++, because it currently doesn't work), or is there 
> another
> approach?

We use -include.  We generate one large application .gch file that 
include tons of things in it.

bash-2.05a$ wc MillenniumFE.ii
  152201  333117 4298858 MillenniumFE.ii

That is the .ii file of the file that is -included.  This generates a 
30-40 MB .gch file.  The application has 279 translation units in it.

I don't know offhand why it works for us and not you.  Random guess, I 
thought I saw something about TAKES_ARG go by recently in another 
context...  Found it, in cppspec.c Devang added 
DEFFAULT_WORD_TAKES_ARG, is this related to why -include doesn't work?

The best win I can think of for g++ would be to create all, and include 
all the headers one can, and change all headers to inlcude all, and 
then precompile all, and link it around under all the various names 
that can be used and fix the can't do more than abs names problem in 
PCH.

This doesn't rely upon -include, works out of the box for all the std 
include files, maximal win, easy to use, just #include one of the 
normal C++ headers before anything else in the .cc files.