Outside the license, the main benefit seems to be that in Clang the different stages are less intertwined than GCC. This is supposed to make developing Clang easier (since you don't have to understand so much), allowing optimizations to be tested and added easier.
On the user side, Clang is well known for providing much better error messages. Some error messages will even suggest possible fixes (you might get something like "Can't assign a pointer to a something, did you mean *pointer?").
The GCC guys have been improving their compiler for a long time, and over the last few years they have been working hard to make GCC easier to work on and optimize. I believe that GCC is usually faster or the binaries are smaller by a few percent, but it's not generally a drastic difference.
GCC speedup is actually quite substantial in math/numerical code (which, in turn, is not as fast as Intel's ICC). Moreover, GCC supports OpenMP, whereas Clang does not. This alone make building several scientific software packages not possible with Clang.
It's important to note though that it has only been recently (starting with GCC 4.4) that I've started to see some _improvement_ over previous GCC versions. GCC 3.x was known to be bloated, buggy and emit poor code for almost every architecture. Open64 was superior in _all_ regargs up to GCC 4.2/4.3 in my opinion.
Clearly, the whole project greatly benefited from Clang's competition.
Agreed. Competition is GREAT, and seeing these two excellent open source compiler offerings engaging in friendly competition means we as end users all benefit, no matter which solution we prefer (or use both, as I assume I'm not the only one doing).
Starting with gcc 4.7 and 4.8 the error message for C++ are also improved [1] and start to get close to clang. The competitions seems to be good for gcc and I like to have the choice between two compilers.
> On the user side, Clang is well known for providing much better error messages. Some error messages will even suggest possible fixes (you might get something like "Can't assign a pointer to a something, did you mean pointer?").*
Here [0] is an example of Xcode leveraging clang to provide valuable feedback. The second picture speaks volumes.
While we're on the subject of static analysis and valuable feedback, you should take a look at PVS-Studio, which is pretty neat as well, and is comparable to what clang can do (as far as I can tell from their blog posts).
On error report: I wrote some programs in C that heavily reply on huge macros to mimic template in C++. The gcc error report is completely useless as it points to the line with the entire function expanded to a single line. Clang is much more clever.
I do not know how clang achieves that, either. BTW, with gcc, I usually do something like this: "gcc -E prog.c | grep -v ^# | indent > prog-fmt.c" This is quite clumsy, though.
http://clang.llvm.org/comparison.html#gcc
Outside the license, the main benefit seems to be that in Clang the different stages are less intertwined than GCC. This is supposed to make developing Clang easier (since you don't have to understand so much), allowing optimizations to be tested and added easier.
On the user side, Clang is well known for providing much better error messages. Some error messages will even suggest possible fixes (you might get something like "Can't assign a pointer to a something, did you mean *pointer?").
The GCC guys have been improving their compiler for a long time, and over the last few years they have been working hard to make GCC easier to work on and optimize. I believe that GCC is usually faster or the binaries are smaller by a few percent, but it's not generally a drastic difference.