We might expect some performance improvements with 10.9.2 due to LLVM 3.4

I'm slightly confused. If LLVM 3.4 requires being compiled on Xcode 5.1, wouldn't Apple have to already be compiling on 5.1 for 10.9.2 and 7.1 to have LLVM 3.4? My point being, I feel like it would be weird for Apple to start compiling 10.9.2 and 7.1 on a different version of Xcode halfway through development?

 

Actually it does. What if the new compiler introduces a behavior difference in the generated code? This could cause additional delays while Apple tracks down issues with code that wasn't modified.

Apple could start using the new compiler for say 10.9.3 but expect a slightly longer time between 10.9.2 and 10.9.3 if they do to allow for extended testing.

 

In that case expect that there may be a delay in 10.9.2 caused by changing the compiler.

 

I hope LLVM 3.4 is a huge improvement. I tried the Intel compiler and was unimpressed.

 

This is an upgrade, not a new compiler. Apple used newer compiler versions for system parts like kernel extensions in the past.

 

Try the PGO and the built-in data prefetch instructions!

 

Those are nice, but so many OSX programs are built with Objective-C, which the Intel compilers do not support. Also, Clang/LLVM is faster at building programs and isn't as picky (ICC crashed for me when I was using it to build Emacs and some X libraries).

It does give Motif programs nice performance, though. The Fortran compiler is also top-notch.