Package com.saxonica.ee.optim

Class CommonSubexpressionPromoter

  • public class CommonSubexpressionPromoter
extends java.lang.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).

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      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

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • CommonSubexpressionPromoter

        public CommonSubexpressionPromoter​(OptimizerEE opt)

    • Method Detail

      • 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.