[Haskell-cafe] Can Haskell outperform C++?

Manuel M T Chakravarty chak at cse.unsw.edu.au
Tue May 15 02:55:22 CEST 2012

Ryan Newton:
> But, anyway, it turns out that my example above is easily transformed from a bad GHC performance story into a good one.  If you'll bear with me, I'll show how below.
>    First, Manuel makes a good point about the LLVM backend.  My "6X" anecdote was from a while ago and I didn't use llvm [1].  I redid it just now with 7.4.1+LLVM, results below.  (The below table should read correctly in fixed width font, but you can also see the data in the spreadsheet here.)
>                    Time (ms)   Compiled File size   Comple+Runtime (ms)
> GHC 7.4.1 O0	   2444	       1241K	
> GHC 7.4.1 O2	   925	       1132K	            1561
> GHC 7.4.1 O2 llvm  931         1133K
> GHC 7.0.4 O2 via-C 684         974K
> So LLVM didn't help [1].  And in fact the deprecated via-C backend did the best!  

I would classify that as a bug.

> [1] P.P.S. Most concerning to me about Haskell/C++ comparisons are David Peixotto's findings that LLVM optimizations are not very effective on Haskell-generated LLVM compared with typical clang-generated LLVM.

There is some work underway to improve the situation, but I am sure more could be done.


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