[wg-camlp4] benchmarks

Hongbo Zhang hongboz at seas.upenn.edu
Tue Feb 12 13:21:58 GMT 2013

On Tue, Feb 12, 2013 at 6:54 AM, Thomas Gazagnaire <thomas at ocamlpro.com> wrote:
>> - Running AST rewriters as independent processes adds about 7% of compilation time with ocamlopt.opt
>> - If we run a single process without marshaling the AST between rewriters, the marginal cost goes below 1% per rewriter.  (This is, basically, the cost of iterating over the AST with objects, matching over each expression to find extension "markers", and rebuilding a deep copy of the AST.)
>> - This can be reduced a lot with proper configuration of the GC (down to about 0.3% of compilation time with ocamlopt.opt, with the same GC config).
>> - It would be interesting to do some timings when dynlinking a lot of different .cmxs plugins in ppx_drivers.
> Thanks for the detailed explanation. This sounds like very good results and strong arguments to replace the complex camlp4 beast by something lighter.
Hi, Thomas, my micro-benchmark(in the previous email) shows fan be as
fast as ast rewriter
> I quite like the idea of having AST rewriter hooks in compiler libs to create easy-to-use compiler variations.
> --
> Thomas
>> (If we link the rewriters statically with a custom version of the compiler itself, assuming a new hook in the compiler allows to plug AST rewriter, we would only pay the marginal cost < 1%.)
>> For a code base like Jane Street's where many "extensions" have to be used everywhere, I suspect that the "independent" ppx processes might become an issue (or maybe not, if compared to camlp4), but the following solutions would work:
>> - Statically linking a "big rewriter" called with -ppx.
>> - Statically linking a version of ocamlopt.opt + all rewriters.
>> - Dynamically linking all rewriters with a single ppx driver (to be confirmed, there would be a small overhead for the dynamic linking itself in addition to the 0.3% marginal cost above).
>> Alain
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-- Regards, Hongbo

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