[LLVMdev] The performance of LLVM vs GCC

[Martin Whitaker]

Hi Duncan,

Duncan Sands wrote:
> Hi Martin,
>
>> Here's a more recent one:
>>
>> http://www.phoronix.com/scan.php?page=article&item=gcc_46_llvm29&num=1
>
> a few comments:
>
> (1) The smallpt benchmark uses openmp which dragonegg supports but clang
> does not.  That's why on the machines with N processors the clang compiled
> binary takes N times as long as the others: it is only using one processor
> unlike the others.
> (2) On the Himeno benchmark dragonegg beats the pants off everyone else.  But
> the benchmark was compiled at -O0 (no optimization!) so this is of no interest.
> (3) GraphicsMagick also uses openmp, see point (1).
>
All benchmarks have to be treated with a healthy degree of skepticism!

For points 1 and 3, I think this is still a justifiable comparison to make - 
the fact that clang doesn't support openmp means it genuinely can't perform as 
well for these particular applications. For point 2, I agree this is a totally 
useless benchmark.

What did strike me is that for the Intel processors there didn't seem to be a 
clear winner or loser, but for the Opteron clang always came last. This 
matches my own experiments on my Athlon based PC. Does this match other 
peoples' experiences?

Martin