Interesting JVM JIT example where the author rewrites code to help the optimiser: http://t.co/9sNIe7d59l (ideally we'd have the reverse!)
miniblog.
Related Posts
C++ compiler beating hand written assembly: https://stackoverflow.com/questions/40354978/why-is-this-c-code-faster-than-my-hand-written-assembly-for-testing-the-collat
If you haven't measured the cycle time of the different instructions, the optimiser can often do better!
The Sista VM, an incredible JIT optimiser for Smalltalk, has now released an alpha:
It's remarkable how much of Emacs' byte-compiler optimiser is unchanged from 1992!