duncan.coutts:
On Wed, 2010-05-05 at 21:24 +1000, Roman Leshchinskiy wrote:
Whenever I do cabal sdist on one of my projects, I get this warning:
Distribution quality warnings: 'ghc-options: -O2' is rarely needed. Check that it is giving a real benefit and not just imposing longer compile times on your users.
This finally got me curious and I did a nofib run to compare -O to -O2. The results are below (this is with the current HEAD).
Is there a real-world example of -O2 causing significantly longer compile times without providing a real benefit? If not, would it perhaps make sense for Cabal to use -O2 by default or even for GHC to make the two flags equivalent?
It should be -O1 for default/balanced optimisations and -O2 for things involving a bigger tradeoff in terms of code size or compile time. so any optimisations in -O2 that GHC HQ believe are a no-brainer for the majority of packages should be moved into -O1.
+1 It might be a good time to revise the set of "balanced" optimizations available at -O1 (-O) level.