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Re: [patch] combined build

From: Dan Nicolaescu
Subject: Re: [patch] combined build
Date: Thu, 15 Nov 2007 11:46:39 -0800

Stefan Monnier <address@hidden> writes:

  > >> This patch provides a minimal support for compiling (the most of)
  > >> emacs C code at once using -combine option supported by never
  > >> versions of GCC. Since an almost everything is compiled each time
  > >> when the compiler is invoked, this mode is not suitable for
  > >> developers. But it might be useful for package builders and other
  > >> peoples who just wants to do './configure && make && make install'
  > >> sequence. This feature also gives GCC a chance to optimize something
  > >> during inter-module analysis.
  > BTW, what kind of benefit are we looking at?
  > Is the resulting executable smaller?  If so by how much?
  > Is it faster?  If so by how much?
  > Is the compilation quicker?

I did this 2 years ago, so I don't have any numbers handy. Maybe Dmitry
has some. 
It should help a bit both the code size (if I remember well about 5%),
and the speed, especially when using -fwhole-program on x86 (in that
case the calling convention for functions that don't have their address
taken can be changed from stack based to register based -- there are
other things too, but AFAIR this is one of the important ones).

Size is easy to look at, but how would you test the speed?

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