[AntonErtl]

As for the market demands on compilers, I hope that this paper influences that in more reasonable directions. In the meantime, I have nothing against having an option (or more) for "optimizations". Enabling new "optimizations" by default however has the effect of miscompiling existing programs and is not such a good idea. At the very least there should be one flag for disabling "optimizations" without disabling optimizations.

Concerning what are optimizations: If the observable behaviour does not change (even when there is undefined behaviour), it's an optimization. Also, register allocation and rearranging stuff in memory is an optimization (because programs that rely on that not changing break on maintenance). Other transformations are, at best, "optimizations". If you have any questions about specific transformations, please ask.