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Re: GCC-3.4.0/PCH - some numbers incl. a bug report


On Thu, 29 Apr 2004, Rene Rebe wrote:

> Hi,
>
> I just reviewed the advantage PCH would offer for one of our C++
> projects. So here are the build times (GNU/Linux, PowerPC, GCC-3.4.0):
>
> A normal build without PCH:
>
>  real    2m26.986s
>  user    2m5.440s
>  sys     0m12.120s
>
> a build including PCH generation:
>
>  real    4m6.156s
>  user    3m32.030s
>  sys     0m23.940s
>
> a build using the existing PCH from the previous build:
>
>  real    2m4.426s
>  user    1m44.230s
>  sys     0m10.840s
>
> So we get a 15% speedup for subsequent build - with a 67% slowdown for
> the first build. Are this expected numbers?
>

I guess your source tree is not optimized for PCH enabled build. General
hint which I have found during MICO hacking to be optimized for PCH build
is: less PCH files you produce during the build, better. So you normaly
end with one header file accumulating all needed header files and this is
used for PCH enabled build. Then you are able to get much better numbers
than you provided above.

Cheers,

Karel
--
Karel Gardas                  kgardas@objectsecurity.com
ObjectSecurity Ltd.           http://www.objectsecurity.com



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