gcc vs. clang builds of 7.8.3 on OS X

[Carter Schonwald]

Maybe it depends on the version of OS X being used? Maybe TLS works
differently pre 10.8  or 10.9?

On Saturday, July 12, 2014, Johan Tibell <johan.tibell at gmail.com> wrote:

> 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
> <javascript:_e(%7B%7D,'cvml','mark.lentczner at gmail.com');>> wrote:
>
>> 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).
>>
>>  Summary:
>>
>>    - 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
>>    <http://www.ozonehouse.com/mark/platform/analysis-Silver-10.9-gcc-vs-clang.html>
>>    - analysis-Silver-10.9-gcc-vs-clang-threaded.html
>>    <http://www.ozonehouse.com/mark/platform/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 greater?
>>
>> 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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>>
>
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