clang's build performance

[Christopher Jones]

Hi,

I cannot answer why, but I can confirm what you have seen. Even on OSX10.9, where the system clang is

MacBookPro ~ > clang -v
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.3.0
Thread model: posix

So I would guess closer to MacPorts clang 3.4 than it is on OSX10.6, build with the system clang is significantly faster than MacPorts…

cheers Chris

On 5 Jul 2014, at 2:08pm, René J.V. Bertin <rjvbertin at gmail.com> wrote:

> In hope it's not completely out of place to discuss this here, but has anyone else noticed that clang's supposedly better build performance (as opposed to gcc) is no longer an accurate selling argument, at least for version 3.4? 
> 
> Comparing build times of a port I'm working on, KDE's rekonq so mostly C++:
> 
>> port clean rekonq ; time port -v destroot rekonq # uses Apple's gcc-4.2 on OS X 10.6.8
> 2:59 total_time
>> port clean rekonq ; time port -v destroot rekonq configure.compiler=clang # uses Apple's clang-3.0 on OS X 10.6.8
> 1:42 total_time
>> port clean rekonq ; time port -v destroot rekonq configure.compiler=macports-clang-3.4
> 4:04 total_time
>> port clean rekonq ; time port -v destroot rekonq configure.compiler=macports-gcc-4.8
> 2:22 total_time
> 
> That's on an i7 with 2 cores x 2 hyperthreads; I'm getting in a bit over 200% CPU when using 4 concurrent build jobs.
> 
> I haven't yet done a similar comparison under Linux, but could this be due to how MacPort's llvm & clang are built?
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