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

Francois Pichet pichet2000 at gmail.com
Sat May 30 21:57:17 PDT 2015

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

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.
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