On 30 September 2011 16:07, Max Bolingbroke <[email protected]> wrote: > I just tried to run David Peixotto's fibon suite with and without the > new analysis, but all the benchmarks time out for me. I've sent him an > email to find out what I'm doing wrong - if he can help me out then I > should be able to post fuller numbers.
David Peixotto's has generously given me some guidance on the use of fibon, and I've been able to get some numbers on how the GHC alias analysis changes things. The results are kind of surprising: runtime gets worse by a geometric mean of 0.5%, with a worst case of 5.45%, at a 13% cost in compile time! So, I can perfectly well believe that the alias analysis is not enough to help LLVM to improve the code in more general examples than the one I considered. However, I'm quite surprised by the result it actually made the code *worse* on average -- I've set it up so my analysis is guaranteed to always return results that are no worse than those from the standard analysis! So either LLVM is actually doing *worse optimisation* when given more precise information, or a 0.5% runtime change is not statistically meaningful. (Or perhaps I've made another error in running Fibon) I'm going to try to understand some of the benchmark examples in more detail to figure out what is going on. Max _______________________________________________ Cvs-ghc mailing list [email protected] http://www.haskell.org/mailman/listinfo/cvs-ghc
