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The Cambridge Haskell Supercompiler (CHSC) | ||
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Overview | ||
--- | ||
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The Cambridge Haskell Supercompiler (CHSC) is a preprocessor which supercompiles programs written in a subset of Haskell. The output is | ||
source code suitable for presentation to the Glasgow Haskell Compiler (GHC) for compilation as standard Haskell. | ||
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The hope is that the process of supercompiling the input makes it more efficient and hence CHSC can be used as a program optimisation | ||
tool. Because of the focus on program optimisation the design of CHSC is somewhat different from that of supercompilers used for | ||
theorem proving: | ||
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* We are careful to never duplicate work that is shared in the input program | ||
* We compile a language which models full Haskell: in particular, we can supercompile strict primops and recursive let bindings | ||
* We care a lot about code duplication and compile time, even if we don't have any good answers yet | ||
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The intention is to eventually integrate the supercompiler into GHC to supercompile the Core language. This will let us truly supercompile | ||
any Haskell program, not just those written in the subset that CHSC knows how to desugar. | ||
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Bugs | ||
--- | ||
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At the time of writing, there are no known bugs in the `master` branch of the supercompiler. However, supercompiling certain programs | ||
(even some of the examples I have provided) has never been observed to terminate due to the supercompilation code explosion problem. | ||
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Using | ||
--- | ||
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If you want to try out the CHSC, use the `test` script: | ||
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$ ./test examples/toys/MapMapFusion.core | ||
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This will print output similar to the following: | ||
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examples/toys/MapMapFusion.core | ||
mapmapfusion & 0.0s & 0.50 & 0.82 & 1.02 \\ | ||
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The fields on the second row are, from left to right: | ||
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1. The name of the benchmark | ||
2. The time taken to supercompile (in seconds) | ||
3. Time taken by GHC to compile to the supercompiled program, as a fraction of the time taken for the input program | ||
4. Runtime of the supercompiled program, as a fraction of that of the input program | ||
5. Total heap allocation by the supercompiled program as a fraction of that of the input | ||
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In addition to supercompiling and running the benchmarks, the test script outputs the supercompiled forms of the programs: | ||
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* The input program (as a valid Haskell program) is placed in `input/examples/toys/MapMapFusion.hs` | ||
* The output program (again, as valid Haskell) is placed in `output/primops/gen/examples/toys/MapMapFusion.hs` | ||
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Naturally, the suffix of this file name varies with the file name that `test` was invoked with. | ||
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You can use `test` with more than one filename if you would like. | ||
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Paper | ||
--- | ||
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A description of the design of CHSC was accepted to the Haskell Symposium 2010, and is available online: | ||
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* [Supercompilation by Evaluation](http://www.cl.cam.ac.uk/~mb566/papers/sbe-hs10.pdf) |