GCC 4.8.0 vs. LLVM Clang 3.3 Compiler Performance

[XorEaxEax]

Glad to see he is now displaying full optimization flags, also glad that he is using -O3.

Still don't understand why he persists in doing openmp benchmark comparisons as they are totally worthless until clang/llvm supports openmp.

He finally acknowledges that testing stuff like ffmpeg yields no real difference as pretty much all performance critical code is in assembly, so why not just _disable_ assembly optimizations? It would definitely be interesting in seeing how these compilers compare when optimizing video compression oriented code, just compile and benchmark x264 with './configure --disable-asm'.

Also had to laugh at the bias when describing the results, in the C-Ray test GCC4.8 was (by my quick estimate) ~10% faster on Intel Core 3960X, ~40% faster on AMD FX-8350 and ~10% faster on Intel Core i3, this result is described by Michael as a 'slight performance edge'.

10%-40% is not a slight performance edge in compiler optimization.

[elanthis]

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.

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.

[Luke_Wolf]

Yeah, the issue is just finding the right benchmark to fully exploit the hardware. Your typical desktop workload is going to be a lot slower since it's mostly single threaded.

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.

[smitty3268]

I'm not surprised at all, anything that is heavily parallel strongly favours the Bulldozer/Pilerdriver architecture, such that in some benchmarks on other sites it trounced the i7 3990X.

Yeah, the issue is just finding the right benchmark to fully exploit the hardware. Your typical desktop workload is going to be a lot slower since it's mostly single threaded.

[Luke_Wolf]

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).

I'm not surprised at all, anything that is heavily parallel strongly favours the Bulldozer/Pilerdriver architecture, such that in some benchmarks on other sites it trounced the i7 3990X.

[leonmaxx]

the FX-8350 performs pretty well in general.

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).

[peppercats]

Interesting, I remember the last time clang was tested using an AMD CPU the performance was abysmal compared to GCC.

edit:
and for being ~$800 cheaper, the FX-8350 performs pretty well in general.

[phoronix]

Phoronix: GCC 4.8.0 vs. LLVM Clang 3.3 Compiler Performance

In preparation for the upcoming release of LLVM 3.3, here is an extensive round of C/C++ benchmarks from GCC 4.8.0, LLVM Clang 3.2, and LLVM Clang 3.3-rc1 to look at the Linux compiler performance. Benchmarks happened from three different systems bearing Intel Core i7 3960X, AMD FX-8350, and Intel Core i3 3217U processors for a diverse look at the performance.

http://www.phoronix.com/vr.php?view=18737