LLVM and TLS

[Jonathan Marler via digitalmars-d-ldc]

I've noticed that on my windows 7 development machine, switching 
between TLS and non-TLS storage has a minimal impact on 
performance (when using DMD).  I haven't tried LDC yet, however, 
on a macbook pro, which uses clang (LLVM) for the linker, using 
TLS has a huge performance impact (much much slower).  Does 
anyone know if this is because of the way LLVM handles TLS 
storage?  I'll have to try using LDC on my windows machine but 
maybe one of you know off hand whether or not LLVM has some 
performance problems with TLS storage. Thanks!