Re: [lmi] Precompiled headers

[Vadim Zeitlin]

On Tue, 22 Dec 2015 13:21:11 +0000 Greg Chicares <address@hidden> wrote:

GC> On 2015-12-22 02:26, Greg Chicares wrote:
GC> > On 2015-12-22 01:33, Vadim Zeitlin wrote:
GC> >> On Tue, 22 Dec 2015 00:28:44 +0000 Greg Chicares <address@hidden> wrote:
GC> >> 
GC> >> GC> It takes three times as long, which is not an argument in favor of
GC> >> GC> upgrading. Can we improve the build time?
GC> >> 
GC> >>  I am pretty sure that using PCH will do it.
GC> > 
GC> > IIRC, you worked on an lmi PCH patch a long time ago, but found that it
GC> > wasn't worthwhile for gcc-3.4.5 . Do you happen to know whether there's
GC> > a working patch in our email archives?
GC> 
GC> Vaclav tried it:
GC> 
GC> http://lists.nongnu.org/archive/html/lmi/2009-06/msg00022.html
GC> | I tried to add precompiled headers support to LMI, with mixed results.
GC> | That is, it works great for Visual C++ (cutting compilation time from 33
GC> | minutes to 4 minutes in my VM), but it doesn't improve gcc compilation
GC> | times (sometimes, it is a tiny bit faster, sometimes even a tiny bit
GC> | slower).
GC> 
GC> Sounds like it won't help us.

 Hello,

 I am not sure which gcc version did Vaclav use, but it definitely wasn't
4.9, so I think the experiment is worth redoing because at least IME with
wx the PCH are definitely worth using, at least with a full rebuild, with
gcc 4.x with x >= 6.

GC> I would tend to conclude that we shouldn't spend time on this.

 For me there is another important benefit in applying PCH-enabling patch
to the mainline: not having the divergences in all source files between it
and my own branch(es) where I definitely want to use PCH with MSVC because
of a huge difference it makes for it. So I'd still like to do it if you
don't object violently.

 I will however try benchmarking the native compiler first to know if I
should be testing PCH with the Cygwin cross-compiler or native one, in case
there is a big difference between them.

 Please let me know if you have any objections to this, otherwise I'll try
to do it "soon", although this might still mean after Christmas.

 Thanks,
VZ