Package com.saxonica.ee.optim

Class CommonSubexpressionPromoter

java.lang.Object
com.saxonica.ee.optim.CommonSubexpressionPromoter
public class CommonSubexpressionPromoter extends Object
This class is responsible for identifying and extracting common subexpressions within an expression. For example the expression (x/y/z = 3 or x/y/z = 4) is turned into (let $zz = x/y/z return ($zz = 3 or $zz = 4). For simplicity, in this initial version: (a) we extract at most one subexpression: the one that has the highest value of instances*cost. (b) we restrict the scope of the search for duplicates to that part of the expression tree that shares the same dynamic context (local variables, focus, etc).

  • Constructor Details

    • CommonSubexpressionPromoter

      public CommonSubexpressionPromoter(OptimizerEE opt)

  • Method Details

    • promoteCommonSubexpressions

      public Expression promoteCommonSubexpressions(Expression in)
      Search for duplicate subexpressions within an expression tree, and if one is found, generate a local variable bound to the common subexpression, replacing the original subexpression with a reference to the new local variable
      Parameters:
      in - the expression to be searched
      Returns:
      the new expression, with common subexpressions promoted; or the original expression unchanged.