Re: inside the GHC code generator

bulat.ziganshin@gmail.com wrote:

* multiple results can be returned via C++ pair template, if this is efficiently implemented in gcc

There's a -freg-struct-return option in 2.x, 3.x and 4.x. I think it's off by default on many architectures.

* recursive definitions translated into the for/while loops if possible

I think recent versions of GCC do a good job of this. See http://home.in.tum.de/~baueran/thesis/ All of this efficiency stuff aside, there's a big problem you're neglecting: GARBAGE COLLECTION. For a language that allocates as much as Haskell I think a conservative collector is absolutely out of the question, because they can't compact the heap and so allocation becomes very expensive. A copying collector has to be able to walk the stack and find all the roots, and that interacts very badly with optimization. All the languages I've seen that compile via C either aren't garbage collected or use a conservative or reference-count collector. The closest thing I've seen to a solution is the technique used in Urban Boquist's thesis, which is to put a static table in the executable with information about register and stack usage indexed by procedure return point, and use that to unwind the stack and find roots. Some C compilers (including gcc) support debugging of optimized code, so it might be possible to parse the debugging tables and extract this information. As far as I know, no one has ever looked into the feasibility of doing this, which is kind of surprising since root-finding is probably the single biggest obstacle to compiling functional languages via C. -- Ben