-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Notes on clang/LLVM + C++ + JIT stuff: //////////////////////////////////////////////////////////////////// // Copyright 2008 Eric Niebler. Distributed under the Boost // Software License, Version 1.0. (See accompanying file // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) #include <iostream> #include <boost/proto/core.hpp> #include <boost/proto/context.hpp> #include <boost/typeof/std/ostream.hpp> namespace proto = boost::proto; proto::terminal< std::ostream & >::type cout_ = {std::cout}; template< typename Expr > void evaluate( Expr const & expr ) { proto::default_context ctx; proto::eval(expr, ctx); } int main() { evaluate( cout_ << "hello" << ',' << " world" ); return 0; } //] wash@Pegasus:~/sandbox$ time clang++ -cc1 -triple x86_64-unknown-linux-gnu - -emit-llvm-bc -x c++ hello.cpp real 0m1.958s user 0m1.676s sys 0m0.276s wash@Pegasus:~/sandbox$ lli hello.bc hello, world wash@Pegasus:~/sandbox$ There's nothing magic about JITing C++, even JITing non-trivial C++. It's basically pointless, because the LLVM bitcode/LLVM assembly generated by a C++ program is absolutely, positively not portable. Starting in the earliest stages of compilation (preprocessing), platform dependencies enter the code (not to mention all the preprocessor workarounds). Add in alignment jazz. Plus sizes. Plus implementation details (GNU expands sizeof and assert in the preprocessor, for example). CXXABI. C++ is not Java, and clang/LLVM are not magic. We can do cool things with clang/LLVM, C++ and JIT, but at the end of the day, C++ is not Java. Other stuff: I think I saw some comments implying that C compilers were faster or better than C++ compilers. I know that I saw people claim that C compilers were faster, better or could optimize better than C++ compilers implemented using expression templates and metaprogramming techniques. Such claims are unfounded. http://clang.llvm.org/performance.html - clang uses limited template metaprogramming techniques, however it is quickly shaping into a solid, production-quality open-source C++ compiler (I have compiled a semi-functional Linux kernel with clang), and it is by far superior to it's C predeccessor GCC when it comes to optimization. Boost.Wave, a standards compliant C preprocessor is implemented using Boost.Spirit. www.ll.mit.edu/HPEC/agendas/proc02/abstracts/mullin.pdf - really smart MIT guy's paper on really cool optimizations, done in C++ with C++ TMP techniques, specifically expressive templates. - -- Bryce Lelbach aka wash http://groups.google.com/group/ariel_devel -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAky1PVkACgkQO/fqqIuE2t6gBwCcDjnYwO8kYzzBu7HOyl6yyAhB UJsAoMfUKrujDLkBHHEOe7Eyep9AJOJi =hYSg -----END PGP SIGNATURE-----