-fmove-all-movables and -freduce-all-givs

[Joern Rennecke]

> I'm currently researching how machine learning algorithms can be 
> employed to discover effective compiler heuristics.  I see from your 
> online documentation that -fmove-all-movables and -freduce-all-givs can 
> sometimes generate slower code.
> 
> These optimizations seem like prime candidates for machine learning 
> because the tradeoffs are not clear (in my mind it seems like the 
> optimizations should always yield speedups).

Only if your processor has an infinite number of registers what can
be addressed with equal cost.