[cfe-dev] Clang on Windows targteing gcc compiles very slowly

Sun May 31 23:42:28 PDT 2015

when i disable multi-thread compile and /MP 
(http://blogs.msdn.com/b/visualstudio/archive/2010/03/08/tuning-c-build-parallelism-in-vs2010.aspx)
i get ~1:12 versus ~1:20 - so that doesn't explain the better speed of VS

Am 31.05.2015 um 23:10 schrieb Reid Kleckner:
> Another thing to consider is that clang-cl doesn't implement /MP, the cl
> flag for multiprocessing. If you are comparing cl with MSBuild to clang-cl
> MSBuild, clang will go slower because it doesn't run multiple compiles in
> parallel.
>
> This, however, doesn't explain the 2x slowdown vs gcc from Edward's
> experimentation. So far all we have are theories on that.
>
> On Sun, May 31, 2015 at 12:34 AM, Dennis Luehring <dl.soluz at gmx.net> wrote:
>
> > another example:
> > https://github.com/RuntimeCompiledCPlusPlus/RuntimeCompiledCPlusPlus
> >
> > compiles in a minute in VS2010 - take years with cl-clang, with
> > compile-bug reports in cl-clang
> >
> > so my "dirty" testbase for finding speed difference and bugs in cl-clang
> > would be
> >
> > -Xerces C++ 3.1.2 (SVN Tag)
> > -DosBox (latest SVN)
> > -RuntimeCompiledCPlusPlus (lastest Git)
> > -ScummVM (SVN)
> >
> >
> >
> > Am 31.05.2015 um 09:06 schrieb Dennis Luehring:
> >
> >> >Huh, that's surprising. Do you happen to
> >> >have VS2013 too? What are you
> >> >compiling? Anything open-source?
> >>
> >> just VS2010 - and a very closed source project, 5 libs, ~50-100kLOC,
> >> around 1200 Warnings (legacy code)
> >>
> >> latest Xerces C++ is another example (does not fully link under cl-clang)
> >> - some warnings
> >> svn co https://svn.apache.org/repos/asf/xerces/c/tags/Xerces-C_3_1_2
> >> VC2010: ~1:59min
> >> cl-clang: stopped at ~6:15 with link error
> >>
> >> or latests DosBox (gives compiler bug report) - many warnings
> >> VC2010: ~1:25
> >> cl-clang: stopped at ~3:19 with compiler-bug report
> >>
> >> it seems that the cl-clang guys should do compiletests against more
> >> dirty projects - not against
> >> the super-clean chrome sources :)
> >>
> >>
> >> Am 31.05.2015 um 08:21 schrieb Nico Weber:
> >> > Huh, that's surprising. Do you happen to have VS2013 too? What are you
> >> > compiling? Anything open-source?
> >> >
> >> > That build is release but with asserts enabled. Disabling asserts saves
> >> > ~30% of runtime, but that would still be 1:30min which is still slower
> >> than
> >> > VS. We only compared to 2013 though, maybe 2010 is faster than 2013?
> >> >
> >> > On Sat, May 30, 2015 at 11:14 PM, Dennis Luehring <dl.soluz at gmx.net>
> >> wrote:
> >> >
> >> > > VS2010 ~1:12min
> >> > > cl-clang (plugin download from 5.5.2015) ~2:15min
> >> > > clang-238562 ~2:11min
> >> > >
> >> > >
> >> > > Am 31.05.2015 um 07:48 schrieb Nico Weber:
> >> > >
> >> > >> Can you try the clang-cl.exe in
> >> > >>
> >> > >>
> >> http://commondatastorage.googleapis.com/chromium-browser-clang/index.html?path=Win/
> >> > >> ?
> >> > >>
> >> > >> On Sat, May 30, 2015 at 10:46 PM, Dennis Luehring <dl.soluz at gmx.net>
> >> > >> wrote:
> >> > >>
> >> > >> > im using the cl-clang vstudio plugin binary from the homepage and
> >> it
> >> > >> > compiles slower (nearly 2 times i think) then cl
> >> > >> >
> >> > >> >
> >> > >> > Am 31.05.2015 um 07:40 schrieb Nico Weber:
> >> > >> >
> >> > >> >> Can you post the cmake invocation you use?
> >> > >> >>
> >> > >> >> In general, we see clang being faster than gcc on linux/mac, and
> >> about
> >> > >> as
> >> > >> >> fast as cl.exe on windows on our bots. It sounds like you don't
> >> > >> configure
> >> > >> >> your build correctly. (clang-built-by-clang is a bit faster than
> >> > >> >> clang-built-by-cl on windows; I don't know how
> >> clang-built-by-clang and
> >> > >> >> clang-built-by-gcc on windows compare. But if you're seeing a 2-3x
> >> > >> >> slowdown, you're probably accidentally doing a debug build of
> >> clang
> >> > >> >> somehow.)
> >> > >> >>
> >> > >> >> On Sat, May 30, 2015 at 9:57 PM, Francois Pichet <
> >> pichet2000 at gmail.com
> >> > >> >
> >> > >> >> wrote:
> >> > >> >>
> >> > >> >> > I just noticed that assert is turned on even in Release on
> >> Windows
> >> > >> >> > Is that on purpose? (seems like a bug to me)
> >> > >> >> >
> >> > >> >> > Anyway if I build clang with "LLVM_ENABLE_ASSERTIONS:BOOL=OFF"
> >> the
> >> > >> build
> >> > >> >> > get stuck at verifier.cpp from LLVMCore. CL.exe is stuck in an
> >> > >> infinite
> >> > >> >> > loop.
> >> > >> >> >
> >> > >> >> > I am using MSVC 2013 Update 5.
> >> > >> >> >
> >> > >> >> > On Sat, May 30, 2015 at 10:30 AM, Reid Kleckner <rnk at google.com
> >> >
> >> > >> wrote:
> >> > >> >> >
> >> > >> >> >> You said you configured in release mode, but assertions might
> >> still
> >> > >> be
> >> > >> >> >> on. That accounts for a 2x slowdown. Otherwise I'd say that we
> >> > >> haven't
> >> > >> >> >> profiled and optimized clang on windows very much.
> >> > >> >> >>
> >> > >> >> >> Sent from phone
> >> > >> >> >> On May 29, 2015 4:51 PM, "Edward Diener" <
> >> > >> >> eldlistmailingz at tropicsoft.com>
> >> > >> >> >> wrote:
> >> > >> >> >>
> >> > >> >> >>> I test Boost libraries mostly on Windows using various
> >> version of
> >> > >> gcc
> >> > >> >> >>> 4.3 and up, VC++ 8.0 and up, and the latest version of clang
> >> which
> >> > >> I
> >> > >> >> build
> >> > >> >> >>> from source using mingw/gcc-4.8.1 in release mode.
> >> > >> >> >>>
> >> > >> >> >>> While clang is a great compiler when it comes to testing code,
> >> > >> getting
> >> > >> >> >>> intelligent error message, and implementing the latest C++
> >> > >> standard,
> >> > >> >> it is
> >> > >> >> >>> noticably slower ( 2x or 3x at minimum ) than the other
> >> compilers I
> >> > >> >> use.
> >> > >> >> >>>
> >> > >> >> >>> The clang command line parameters usually being used are
> >> usually
> >> > >> along
> >> > >> >> >>> the lines of:
> >> > >> >> >>>
> >> > >> >> >>> -c -x c++ -O0 -g -fno-inline -Wall -g -march=i686 -m32
> >> > >> >> >>>
> >> > >> >> >>> with the addition of 'std=c++11' occasionally depending on the
> >> > >> test.
> >> > >> >> >>>
> >> > >> >> >>> Does anybody have any idea why clang is so much slower than
> >> any of
> >> > >> the
> >> > >> >> >>> other compilers I use ? It does not seem to matter whether it
> >> is in
> >> > >> >> C++03
> >> > >> >> >>> mode or C++11 mode, it is noticeably slower than the other
> >> > >> compilers.
> >> > >> >> >>>
> >> > >> >> >>> _______________________________________________
> >> > >> >> >>> cfe-dev mailing list
> >> > >> >> >>> cfe-dev at cs.uiuc.edu
> >> > >> >> >>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >> > >> >> >>>
> >> > >> >> >>
> >> > >> >> >> _______________________________________________
> >> > >> >> >> cfe-dev mailing list
> >> > >> >> >> cfe-dev at cs.uiuc.edu
> >> > >> >> >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >> > >> >> >>
> >> > >> >> >>
> >> > >> >> >
> >> > >> >> > _______________________________________________
> >> > >> >> > cfe-dev mailing list
> >> > >> >> > cfe-dev at cs.uiuc.edu
> >> > >> >> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >> > >> >> >
> >> > >> >> >
> >> > >> >>
> >> > >> >>
> >> > >> >>
> >> > >> >> _______________________________________________
> >> > >> >> cfe-dev mailing list
> >> > >> >> cfe-dev at cs.uiuc.edu
> >> > >> >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >> > >> >>
> >> > >> >
> >> > >> > _______________________________________________
> >> > >> > cfe-dev mailing list
> >> > >> > cfe-dev at cs.uiuc.edu
> >> > >> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
> >> > >> >
> >> > >>
> >> > >>
> >> > >
> >> >
> >>
> >>
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