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Re: precompiled headers can cause big slowdowns
From: |
Fergus Henderson |
Subject: |
Re: precompiled headers can cause big slowdowns |
Date: |
Thu, 19 Apr 2001 17:19:35 +1000 |
In mail to address@hidden,
On 18-Apr-2001, Stan Shebs <address@hidden> wrote:
> Exactly, and that's why our cpp-precomp support includes -cpp-precomp
> and -no-cpp-precomp flags to explicitly control the choice. cpp-precomp
> works by parsing all of its input and tracking xrefs, so it will always
> be slower than a plain preprocessor. The win comes if the xrefs lead
> into a precompiled header, which is an indexed mappable thing and
> very efficient to access randomly. Unfortunately for people porting,
> the only standard precompiled headers are for Cocoa or Carbon, plus
> there is a "libc.h" that you could add to get all of your standard
> system headers in precompiled form; but a "pristine" Unix program won't
> include libc.h and won't use any Mac headers, so it doesn't benefit
> from the use of cpp-precomp, and may in fact compile more slowly.
In that case, it might even be a good idea to patch autoconf so that
on Darwin it includes `-no-cpp-precomp' in $CC by default.
--
Fergus Henderson <address@hidden> | "I have always known that the pursuit
| of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.
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