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

[Edward Diener]

On 5/30/2015 10:30 AM, Reid Kleckner wrote:
> You said you configured in release mode, but assertions might still be
> on. That accounts for a 2x slowdown.

LLVM_ENABLE_ASSERTIONS is off.

> 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
> <mailto: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.