LLVM Clang vs. GCC On Fedora 21 With A High-End Xeon

[phoronix]

Phoronix: LLVM Clang vs. GCC On Fedora 21 With A High-End Xeon

The latest weekend benchmarks up on Phoronix are comparing Fedora 21's GCC and LLVM Clang code compilers to see what's the fastest for an Intel Xeon E5-1680 v3 rig with sixteen threads...

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

[souenzzo]

for curiosity, how about GPU vs. CPU with Gallium LLVM?

[Marc Driftmeyer]

How about you test the compilers with OpenMP disabled? I already know once OpenMP 4 is mainlined into LLVM/Clang GCC won't win a single metric.

[the303]

How about you test the compilers with OpenMP disabled? I already know once OpenMP 4 is mainlined into LLVM/Clang GCC won't win a single metric.

Interesting. What I see is that GCC wins real (also non-OpenMP) library benchmarks (i.e. Bullet) and loses on synthetic bullshit benchmarks which makes me assume they have specifically tuned optimizations for some benchmarks.

How will OpenMP4 will make Clang win i.e. Bullet? Software using OpenMP will be real libraries not some synthetic benchmark suite. How will Clang act different on that matter Mr. Troll unless OpenMP is magic and optimizes even if you dont use the #pragma's?

Anyway, GCC error messages are disasters and wastes lots of time in total while searching for the real info in the messages. Also, way slow to compile with -O0. So you go, Clang.

[fincan]

What is the benefit of LLVM Clang? GCC and LLVM produce machine code at the end. Actually I couldn't understand differences between GCC and LLVM. Can anybody explain me shortly, please?

[Michael]

What is the benefit of LLVM Clang? GCC and LLVM produce machine code at the end. Actually I couldn't understand differences between GCC and LLVM. Can anybody explain me shortly, please?

Really need to read more Phoronix.... The differences have been extensively covered many times rather routinely in GCC vs. Clang articles.

[smitty3268]

What is the benefit of LLVM Clang? GCC and LLVM produce machine code at the end. Actually I couldn't understand differences between GCC and LLVM. Can anybody explain me shortly, please?

In order of importance:

1. Licensing. BSD vs GPLv3 codebase.
2. Embedding. You can use LLVM as a library in your app pretty easily, while GCC is meant strictly as a standalone compiler and not a library.
3. GCC is an old codebase that has been around for a long time. Lot's of legacy ugly C code. LLVM brings a modern object-oriented C++ codebase, that's a lot easier to hack on.
4. LLVM brings a couple of advantages in faster compile times and better diagnostic messages. How much that matters to users is pretty debatable. As long as performance doesn't match GCC, probably not a lot.

[CaptainBlood]

Indeed,
Despite compile time is interesting, generated code performance is what really matters IMHO.

[n3wu53r]

Indeed,
Despite compile time is interesting, generated code performance is what really matters IMHO.

Except for developers clang > gcc. The error messages are infinitely more helpful then anything gcc can produce.

[geearf]

Indeed,
Despite compile time is interesting, generated code performance is what really matters IMHO.

If your code is compatible you could use LLVM for dev and GCC for final release.
Waiting for your code to be compiled is a major hassle.