[SYSTEMDS-2801] Rewrite rule to remove (par)for-loops over empty sequences.

[pdamme]

This commit adds a new StatementBlockRewriteRule removing (par)for-loops which are known to iterate over an empty sequence, and, thus, will not perform a single iteration. This works if the loop's from, to, and increment are constants (possibly DML script arguments, and after constant folding). Furthermore, OptimizerUtils has a new flag determining whether this rule shall be applied. In ProgramRewriter's default rule sequence, this new rule is inserted directly after the removal of unnecessary branches, since they have a lot in common. Merging subsequent blocks is done once afterwards if any of removing unnecessary branches or removing
(par)for-loops shall be applied.

[phaniarnab]

Thanks for adding this rewrite.
One suggestion: In general, adding a test case might be a good idea. You can execute a script (local and spark) with and without the rewrite and match the results.

[pdamme]

Good idea. I will add a test case soon.

[mboehm7]

LGTM - welcome to SystemDS @pdamme and thanks for the patch. During the merge, I fixed a few related for/parfor issues (for correctly handling special values like NaN/Inf/-Inf), fixed the issue of my previous commit, simplified and generalized the rewrite a bit, and added the tests you already discussed. The test simply checks that after this rewrite, we do common subexpression elimination of ops before and after the loop.

print(sum(X));
for(i in seq(NaN,1))
  print("Iteration "+i)
print(sum(X))