Clang vs GCC - which produces better binaries?

Question

I'm currently using GCC, but I discovered Clang recently and I'm pondering switching. There is one deciding factor though - quality (speed, memory footprint, reliability) of binaries it produces - if gcc -O3can produce a binary that runs 1% faster or takes 1% less memory, it's a deal-breaker.

Clang boasts better compile speeds and lower compile-time memory footprint than GCC, but I'm really interested in benchmarks/comparisons of resulting compiled software - could you point me to some or describe your experiences?

Answer 1

The only way to determine this is to try it. FWIW I have seen some really good improvements using Apple's LLVM gcc 4.2 compared to the regular gcc 4.2 (for x86-64 code with quite a lot of SSE), but YMMV for different code bases. Assuming you're working with x86/x86-64 and that you really do care about the last few percent then you ought to try Intel's ICC too, as this can often beat gcc - you can get a 30 day evaluation license from intel.com and try it.

Answer 2

Phoronix did some benchmarks about this, but it is about a snapshot version of Clang/LLVM from a few months back. The results being that things were more-or-less a push; neither GCC nor Clang is definitively better in all cases.

Since you'd use the latest Clang, it's maybe a little less relevant. Then again, GCC 4.6 is slated to have some major optimizations for Core 2 and i7, apparently.

I figure Clang's faster compilation speed will be nicer for original developers, and then when you push the code out into the world, Linux distro/BSD/etc. end-users will use GCC for the faster binaries.

Answer 3

The fact that Clang compiles code faster may not be as important as the speed of the resulting binary. However, here is a series of benchmarks.