Why is everyone itching to get off of GCC? Or is it all just posturing, to get GCC to work harder now that it has competition?
It'll be nice to have a BSD-licenced GCC equivalent for distribution with FreeBSD/OpenBSD, too.
Clang also has REALLY great error messages compared to GCC. It will tell you exactly where you forgot a comma, semicolon, quote, etc. instead of randomly pointing to some line around the error in question.
Apple and various BSD's stopped updating GCC around version 4.2, the last GPLv2 version, which is approximately 4 years old now. For people who only develop on those platforms, this is what "GCC" means. So when someone from Apple or someone with an obvious BSD bias talks about how much better clang is than "GCC", they're usually talking about how much better clang is than an old unmaintained version of GCC.
clang does have strengths, but when we make comparisons, we should be clear about what it is we're comparing.
Saying we're comparing old versions isn't really useful unless the new versions have actually addressed the relevant issues.
If you're comparing clang to just GCC 4.2, then say that. If you've compared it with recent versions of GCC too, then say that.
$ gcc -v
...
gcc version 4.6.2 20120120 (prerelease) (GCC)
Also when speaking of GCC and how old and full of cruft it is, you need to realize that it's code base is being continously improved with each new release with a strong focus on modularity. It's not the same codebase as it was back in 1987.
I'm very happy Clang/LLVM exists and progressing at a great pace as I see increased availability of open source compiler toolchains as something awesome. Also LLVM really does have some great features like the best-in-class error reporting and it also serves an undeniable purpose as a jit framework for numerous projects.
That said I don't understand those trying to push the idea of GCC being obsolete (unless they are nurturing some political/licence based crusade) as it's a very mature compiler toolchain targeting a large number of architectures and (atleast for me) quite importantly generating faster code than Clang/LLVM.
Also the notion that companies would be afraid of GCC strikes me as odd given that we have Red Hat, IBM, Google, CodeSourcery, Suse etc employing full-time GCC developers.
I hope to see these compiler toolchains continously going neck to neck in the future and thus provide the open source ecosystem with two first class options each with their respective strenghts.
Afraid? I expect that these companies have spent serious money on lawyers to figure out whether GPL 3 was acceptable for them before committing to it.
Also, Mac OS supports OpenCL (http://en.wikipedia.org/wiki/OpenCL). One could argue that that makes the compiler more a part of the OS than "just another application that runs on it". If they used GPL code there, a perceived risk could be that they could be forced to make their OS GPL.
It also increases flexibility for developers. Perhaps I prefer to use Clang for its better error messages, or because I find it easier to target at a new platform that I'm working on. If the code already runs under Clang, then that's work I don't have to do. Clang can also be used as an independent parser more easily for GCC, so tools that use it to generate code browsing information or the like benefit from the code already being parseable with Clang.
Compiling under another compiler will also catch more of the cases in which you're depending on non-portable behavior or extensions, which increases the likelihood that you will be able to run it under static analyzers like Coverity, Clang Analyzer, Klee, Splint, or the like.
Basically, beyond wanting to move away from GCC, there is real value in putting work into making sure that everything compiles under another compiler. It's like making sure your web site works on multiple browsers; it can help you catch errors earlier, allow people to use better debugging tools, widen your audience, and help future-proof you.
Now, there are some people who are itching to get away from GCC. For one thing, it is a bigger, older, wartier project, that is harder to work with. People find Clang and LLVM more modular and extensible. For another, there are some companies that are deathly afraid of the GPLv3, and won't touch anything to do with it (Apple in particular, as well as some other embedded device manufacturers I believe). But there are many reasons for wanting to make sure that your software compiles under Clang, and not all of them mean that you want to ditch GCC, just that Clang provides additional value as well.