It seems like auto-vectorization to SIMD code may be an ideal strategy (e.g. Java) since it seems that the conditions to get any performance improvement have to be very particular and situational... which is something the compiler may be best suited to handle. Thoughts?
The things is that using SIMD efficiently often requires you to organize your data and your algorithm differently, which is something that the compiler can't do for you. Another problem is that the compiler doesn't know how often different code paths will be executed so it can't know how to use SIMD in the best way (that could be solved with profile guided optimization, though). Alignment restrictions are another thing that can cause problems. For those reasons auto-vectorization only works in the simplest of cases. But if you want auto-vectorization, GDC and LDC already do it.
I recommend watching Manu's talk (as Kiith-Sa has already suggested):
http://youtube.com/watch?v=q_39RnxtkgM
