[jira] [Created] (SYSTEMML-2168) New rewrite for removal of unnecessary right indexing

["Matthias Boehm (JIRA)" <ji...@apache.org>]

Matthias Boehm created SYSTEMML-2168:
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             Summary: New rewrite for removal of unnecessary right indexing
                 Key: SYSTEMML-2168
                 URL: https://issues.apache.org/jira/browse/SYSTEMML-2168
             Project: SystemML
          Issue Type: Task
            Reporter: Matthias Boehm


In several algorithms like {{scripts/algorithms/glm-predict.dml}}, we see unnecessary right indexing operations that are not yet automatically removed. For example, in the following script
{code}
y_prob [, 1]  = exp (linear_terms);
y_prob [, 2]  = 1.0 - y_prob [, 1];
{code}
the second access to {{y_prob [, 1]}} causes an unnecessary indexing operations and intermediate. We should rewrite this pattern to directly consume the output from {{exp (linear_terms)}} instead.

In detail, this task entails the following steps, which might be a good opportunity to get in touch with SystemML's internal representation of high-level operators:
* Create a new test case for this rewrite in package {{org.apache.sysml.test.integration.functions.misc}} similar to other test classes prefixed with {{Rewrite*}}.
* Add a new rewrite to {{RewriteAlgebraicSimplificationDynamic}} to recognize the pattern of {{Indexing(LeftIndexing(X, y, indexrange1),indexrange2)}} with {{indexrange1==indexrange2}} and rewrite this to {{y}}. Note that there is a rewrite that replaces two subsequent leftindexing operations with an append, so this new rewrite should be invoked before {{fuseLeftIndexingChainToAppend}}.




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