Top-of-trunk clang from http://llvm.org/apt/ takes ~2.1 seconds on my machine to preprocess the file to /dev/null. warp (compiled with -O4 -frelease -fno-bounds-check) takes ~2.8 seconds.

So this test case is faster with clang even without precompiled headers. It is hard to make a benchmark for clang's precompiled headers because the AST is lazy-loaded from the PCH. You would have to actually have code use values from the header.

EDIT: I forgot another advantage of clang: the preprocessing and compilation and assembly are all done within the same process, eliminating process creation overhead.

http://clang.llvm.org/docs/Modules.html

When they're usable for C++, there should be little reason to use any special preprocessor, since every header file (not just a static common set) need only be compiled once into a binary format rather than being included into N source files. It can't happen any sooner for me... but as of recently, they're still very broken, so I'm still waiting.

Nope, it's not, for all X.

I know of a project that takes around 3 hours to build with Clang when you do a "make all".