[SYSTEMDS-1659] New rewrite eliminate unnecessary aggregates

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Done
• Fix Version/s: SystemML 0.15
• Component/s: Compiler
• Assignee: Matthias Boehm
• Reporter: Matthias Boehm
• Created: 03/Jun/17 01:46
• Updated: 09/Sep/17 01:32
• Resolved: 03/Jun/17 21:49

Description

There are some example scripts which use unnecessary aggregations for convenience of a consistent specification - hence, we should automatically eliminate these unnecessary aggregates, via a simple static rewrite. For example, in below script, we should remove the unnecessary rowSums, but the same applies to min-min, max-max, sum_sq-sum.

 # nn lib - cross_entropy_loss::forward (returns only loss)
 N = nrow(y)
 eps = 1e-10  # numerical stability to avoid log(0)
 losses = rowSums(-y * log(pred+eps))
 loss = sum(losses) / N