[mian2zi3]

> It would be very hard to accurately account for a microprocessor's out-of-order instruction issue in a compiler.

This is true. However, a lot of modern processors do in-order execution, they just aren't made by Intel or AMD for desktops: GPUs, network processors, SIMD DSPs, etc. When I was hacking compilers (6 years ago), compiling for these processors presented difficult challenges and there was a real market for new compiler technology. One project was for a network processor that was not only in-order, but it was not interlocked: correctness depended on the compiler having an exact model of the processor's pipeline. Some registers were not registers, but latches. They got new values every cycle, so if you didn't gab a value on the right cycle, it was gone forever.