gcc vs. clang builds of 7.8.3 on OS X
johan.tibell at gmail.com
Sat Jul 12 21:20:24 UTC 2014
I thought clang was slower than gcc because clang doesn't support thread
local variables (in some form we need) and therefore GC performance
suffered a lot on clang.
On Sat, Jul 12, 2014 at 9:27 PM, Mark Lentczner <mark.lentczner at gmail.com>
> In building the OS X bindist for 7.8.3, I had to choose which of several
> ways to build it. In particular, I could build it with a newere Xcode,
> which uses clang, or an older Xcode which uses gcc. I decided to nofib
> benchmark the variations and see before I released. Here is what I found...
> I compared two candidate builds:
> - x86_64 architecture
> - targeted at OS X 10.7 and later
> - one built with Xcode 5.1 on 10.9, which uses clang
> - one built with Xcode 4.5 on 10.8, which uses gcc
> I installed both bindists, side-by-side on the same machine: a 10.9
> machine, with Xcode 5.1, which uses clang. The machine is a MacMini, 2.5GHz
> Intel Core i5 (dual core, reports as 4 cpus).
> - clang build was always faster
> - non-threaded was -3.2% run-time
> - threaded was -7.3% run-time
> - clang's improvement in GC run-time was better than -10%
> - clang builds were significantly bigger
> You can find the details here:
> - analysis-Silver-10.9-gcc-vs-clang.html
> - analysis-Silver-10.9-gcc-vs-clang-threaded.html
> The only concern is that the binary sizes were significantly bigger: +230%
> - I haven't investigated more, but I'm wondering if nofib doesn't strip the
> binaries before measuring, and perhaps clang's debugging info is much
> Next up... we are evaluating a bindist built with the HPC Mac OS X gcc
> compiler (based on gcc 4.9)... and preliminary results are looking even
> better! Stay tuned...
> - Mark
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