Intel Broadwell: GCC 4.9 vs. LLVM Clang 3.5 Compiler Benchmarks
In scientific tests like HMMer, MAFFT, and MrBayes, GCC continues leading over Clang with these latest stable releases on Fedora 21.
Clang still leads over GCC in SciMark.
Clang leads by small margins in a few of the SciMark micro-benchmarks but it's the Dense LU Matrix Factorization and Jacobi tests where Clang really runs in front. This isn't anything Broadwell specific but can be found with other CPUs on Clang too.