http://benchmarksgame.alioth.debian.org/u64q/compare.php?lan...
You can see like most Swift benchmarks, its compiling with the -Ounchecked flag and using C.
-edit- I have no doubts of LLVM's capabilities. It just seems like Swift is probably already taking advantage of its optimizations.
https://github.com/apple/swift/commit/259d57bbe7784955108caa...
The problem was that the print operations was being done character-by-character and it resulted in the printing being a significant overhead in the execution of the tests themselves. With this change they saw a speed up of many times simply because it was using buffered output.
The Go compiler performs nowhere near the level of optimization that LLVM does; LLVM is years and years ahead. However, LLVM is fundamentally a C compiler and so there can be impedance mismatch between Swift and LLVM. Hence SIL. This is what you're seeing, and once the gap is closed then Swift will reap the benefits of the hundreds of optimizations in LLVM.
fannkuch-redux looks near, mandelbrot looks near, n-body…
Swift is new to Linux; there's a new compiler snapshot about every 10 days. Swift has only been available on the benchmarks game 3 months for people to contribute programs. Early days :-)