Handling out of order execution

Question

I recently stumbled upon this Wikipedia article. From my experience with multi-threading I am aware of the multitude of issues caused by the program being able to switch threads

Answer 1

Let's be clear - out of order execution refers to the processor execution pipeline not to the compiler per se as your link clearly demonstrates.
Out of order execution is a strategy employed by most modern CPU pipelines that allows them to re-order instructions on the fly to typically minimise read/write stalls which is the most common bottleneck on modern hardware due to the disparity between CPU execution speeds and memory latency ( i.e how fast my processor can fetch and process compared to how fast I can update the result back to RAM ).
So this is primarily a hardware feature not a compiler feature.
You can override this feature if you know what you're doing typically by use of memory barriers. Power PC has a wonderfully named instruction called eieio ( enforce in order execution of i/o) that forces the CPU to flush all pending reads and writes to memory - this is particularly important with concurrent programming ( whether that be multi-threaded or multi-processor ) as it ensures that all CPUs or threads have synchronised the value of all memory locations.
If you want to read about this in depth then this PDF is an excellent ( though detailed ) introduction.
HTH