Decoupling GCC From Debian By Using LLVM/Clang

Back in March it was shared that LLVM's Clang compiler can build much of the Debian archive. This week at DebConf a status update was shared on using LLVM/Clang as an alternative compiler to GCC within Debian.

Sylvestre Ledru's presentation was entitled "Build Debian with another compiler" and was described at the Managua, Nicaragua event as "After extending Debian with two new kernels, Debian will soon be able to be built with a new free C, C++ and objc compiler called Clang. Based on LLVM, this compiler is now close to gcc on many different aspects (performances, build time, level of support of C and C++). This talk will present the current status of a clang-build version of Debian, the next steps and evolutions."

When beginning his 45-minute presentation, Sylvestre Ledru was quick to make it clear that his intentions on using LLVM/Clang to build the Debian package archive isn't for some GPL vs. BSD licensing ideology, anything to do with Apple, or on the basis of any other non-technical merits. His reasoning for playing with Clang in the Debian world is because "we can" and "because it's fun." [Though to some laughter, shortly after mentioning this, the power to the building was briefly lost. There were storms in Managua on Tuesday afternoon.]

In addition, he elaborated that using LLVM/Clang to build Debian packages only leads to better and more portable code within the archive. If the packages can be built with multiple compilers rather than being bound to just the GNU Compiler Collection, it's to everyone's benefit.

He's also doing this work with an aim to decouple GCC in Debian. Just as the Linux kernel has been decoupled within Debian thanks to the Debian GNU/Hurd and Debian GNU/kFreeBSD kernel ports, he wants to achieve the same with regard to compilers.

The plan at this point isn't to be like FreeBSD where they are using Clang by default and deprecated GCC (that's also what's been done with Apple OS X), but simply to better support LLVM/Clang as an alternative for users and developers. The switching of the base compiler is one of many features of FreeBSD 10.

It was also during this DebConf 12 presentation that the GCC vs. LLVM/Clang diagnostics / error messages were brought up along with briefly talking about the performance between the different compilers in terms of generated code and build times. For the latest benchmarks on this matter, see last month's 11-Way Intel Ivy Bridge Compiler Comparison.

The latest results of building the Debian archive with Clang are available from clang.debian.net. At the moment there's about 12% of the Debian packages that aren't yet building correctly under the Apple-sponsored open-source compiler.