GCC 4.8.0 vs. LLVM Clang 3.3 Compiler Performance

[rogerdpack]

compiler optimization

(Sorry I didn't read too closely if it already does this, and didn't look in the source to check). Anyway one thought is "is this using gcc -march=native"? and another might be to use gcc's profile guided optimization for it. And/or clang's equivalent if it exists.
Cheers.
-roger-

[leonmaxx]

That is another possible conclusion, yes.

Or this:

weakly parallelizable algorithm

Thanks.

[leonmaxx]

Except that it only was faster in two tests (in one of them only on one single CPU out of 3) and slower in everything else? (I don?t count compile times as tests).

But you summarized nicely how misleading the text of this article is - again

Under "next release" i mean Clang 3.4 or later... Sorry for my bad English.

[ArneBab]

Nope, this means that clang compiled single thread perfomance equals 2-4 gcc threads.

Nope: You cannot distinguish between a weakly parallelizable algorithm and compiler performance. To get good data, you would also have to provide a GCC run without openmp: That would show the speedup due to OpenMP.

[ArneBab]

I'm very surprised about FX perfomance in some tests.

Clang: seems like next release will finally beat GCC, and be a good replacement for it (except OpenMP).

Except that it only was faster in two tests (in one of them only on one single CPU out of 3) and slower in everything else? (I don?t count compile times as tests).

But you summarized nicely how misleading the text of this article is - again

[curaga]

That is another possible conclusion, yes.

[leonmaxx]

The openmp comparisons do have some merit. For example graphicsmagick here, it is less than 2x on the 8-core bulldozer: bad quality parallelization there.

Nope, this means that clang compiled single thread perfomance equals 2-4 gcc threads.

[curaga]

The openmp comparisons do have some merit. For example graphicsmagick here, it is less than 2x on the 8-core bulldozer: bad quality parallelization there.

[smitty3268]

Well here's the thing... that's not really true for one simple reason a desktop workload unlike a benchmark (outside of gaming) doesn't consist of running a single application at a time, just an example from myself I've got firefox open with a number of tabs, my IDE, a konsole, my chat clients and dolphin, as well as stuff like dropbox running in the background. any one of these (ignoring the coding and thus compiling) is not particularly heavily threaded but since I'm running all these things I'm taking advantage of more cores. It's certainly not enough to push it up to beating a 3990X but that's besides the point.

Except on a desktop workload, all those background apps are usually idle (at least enough that all of them put together can run on a single core without problems), and you're just waiting on whatever you have active at the moment. Which is usually single threaded.

A lot of times, even stuff that is heavily threaded, like a game, will still be limited by the speed of a single thread, because the work they do on the background threads is relatively limited compared to the main one.

You need to find something that truly breaks up equal amounts of work on 8+ threads to make the AMD chips look good right now.

[Yorgos]

All those apps are sitting there idle not doing a damn thing most of the time. You don't need much hardware for apps that block and wait for user input for 99% of their life. A single-core Atom can do everything you just listed without breaking a sweat.

Stop internet pollution.