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APReF: Automatic Parallelizer of REcursive Functions

This is a source-to-source Haskell compiler that automatically identifies and rewrites recursive functions in a parallel form.

Optimizations implemented:

  • Automatic parallelization
  • Constant folding
  • Reassociation of terms for commutative operations
  • Symbolic simplification of scan operations

References

Automatic Parallelization of Recursive Functions with Rewriting Rules
Rodrigo C. O. Rocha, Luís F. W. Góes, Fernando M. Q. Pereira
Journal of Science of Computer Programming, 2018

An Algebraic Framework for Parallelizing Recurrence in Functional Programming
Rodrigo C. O. Rocha, Luís F. W. Góes, Fernando M. Q. Pereira
SBLP 2016 - Brazilian Symposium on Programming Languages

Example

Given the following sequential recursive function:

f :: Integer -> [Integer]
f 0 = []
f n = [n] ++ f(n-1) ++ [n]

the source-to-source compiler is able to rewrite it as in the following parallel version:

f_g_1 :: Integer -> [Integer]
f_g_1 i = [i]
f_g_2 :: Integer -> [Integer]
f_g_2 i = [i]
f :: Integer -> [Integer]
f 0 = []
f n = let k = n
      in (parFoldr (++) (map f_g_1 (reverse [1..k]))) ++ [] ++
         (parFoldr (++) (map f_g_2 [1..k]))

Usage

By passing a Haskell file to the source-to-source compiler, any parallelizable function will be rewritten in their parallel counterparts. Auxiliary packages and functions will also be added.

python apref.py -f <haskell-file> --scan --constfold

The flag '--scan' enables a scan-based optimization. Similarly, the '--constfold' enables a constant folding optimization.