gcc vs. clang builds of 7.8.3 on OS X

[Mark Lentczner]

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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