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

[Mark Stephenson]

Sorry to bother you,

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).

Can you please let me know for which applications these optimizations 
are detrimental to performance?  And do you have any intuition as to why 
they are detrimental?

Thanks a lot,
Mark Stephenson

p.s. - I've been using the Open Research Compiler to perform my 
research, but I am now looking to switch over to gcc and g77.