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List:       kde-devel
Subject:    Re: Faster startups by fixing C++ object files before linking ( 30-50% faster startups )
From:       Waldo Bastian <bastian () kde ! org>
Date:       2001-07-27 14:49:40
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On Thursday 26 July 2001 08:34 pm, Ian Reinhart Geiser wrote:
> On Thursday 26 July 2001 06:01 pm, Leon Bottou wrote:
> > Reading Waldo Bastian's text on C++ shared libraires gave me some ideas.
> > Eventually I spent a few nights trying them.
> >
> > The proposed scheme modifies the object files before linking
> > in a way that reduces the number of expensive relocations.
> > Startup times are reduced by 30 to 50%.
> >
> > See the attached files for details.
>
> I may be confusing things but is this not about the same idea as
> precompiled headers?  

No.

> It sounds similar but I could be mistaken.  Could
> someone please explane this in a little more detail?

Instead of

1: Call other_lib::some_func
2: Call other_lib::some_func
3: Call other_lib::some_func
4: Call other_lib::some_func
...

It changes this in:

1: Call same_lib::some_func_stub
2: Call same_lib::some_func_stub
3: Call same_lib::some_func_stub
4: Call same_lib::some_func_stub
...
some_func_stub: Call other_lib::some_func

Since it is is expensive to link other_lib::some_func but rather cheap to 
link same_lib::some_func_stub this replaces 4 expensive link actions with 4 
cheap ones and 1 expensive one. These link actions are done at startup.

Cheers,
Waldo
-- 
Andrei Sakharov, Exiled 1980-1986, USSR, http://www.aip.org/history/sakharov/
Dmitry Sklyarov, Detained 2001-????, USA, http://www.elcomsoft.com/
 
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