Class Optimizer

java.lang.Object
net.sf.saxon.expr.Optimizer
All Implemented Interfaces:
Serializable

public class Optimizer extends Object implements Serializable
This class performs optimizations that vary between different versions of the Saxon product. The optimizer is obtained from the Saxon Configuration. This class is the version used in Saxon-B, which in most cases does no optimization at all: the methods are provided so that they can be overridden in Saxon-SA.
See Also:
  • Field Details

  • Constructor Details

    • Optimizer

      public Optimizer(Configuration config)
      Create an Optimizer.
      Parameters:
      config - the Saxon configuration
  • Method Details

    • getConfiguration

      public Configuration getConfiguration()
      Get the Saxon configuration object
      Returns:
      the configuration
    • makeGeneralComparison

      public BinaryExpression makeGeneralComparison(Expression p0, int op, Expression p1, boolean backwardsCompatible)
      Create a GeneralComparison expression
      Parameters:
      p0 - the first operand
      op - the operator
      p1 - the second operand
      backwardsCompatible - true if XPath 1.0 backwards compatibility is in force
      Returns:
      the constructed expression
    • optimizeCopy

      public Expression optimizeCopy(Expression select) throws XPathException
      Attempt to optimize a copy operation. Return null if no optimization is possible.
      Parameters:
      select - the expression that selects the items to be copied
      Returns:
      null if no optimization is possible, or an expression that does an optimized copy of these items otherwise
      Throws:
      XPathException
    • makeClosure

      public Value makeClosure(Expression expression, int ref, XPathContext context) throws XPathException
      Make a Closure, given the expected reference count
      Parameters:
      expression - the expression to be evaluated
      ref - the (nominal) number of times the value of the expression is required
      context - the XPath dynamic evaluation context
      Returns:
      the constructed Closure
      Throws:
      XPathException
    • makeSequenceExtent

      public ValueRepresentation makeSequenceExtent(Expression expression, int ref, XPathContext context) throws XPathException
      Make a SequenceExtent, given the expected reference count
      Parameters:
      expression - the expression to be evaluated
      ref - the (nominal) number of times the value of the expression is required
      context - the XPath dynamic evaluation context
      Returns:
      the constructed Closure
      Throws:
      XPathException
    • convertPathExpressionToKey

      public Expression convertPathExpressionToKey(PathExpression pathExp, ExpressionVisitor visitor) throws XPathException
      Examine a path expression to see whether it can be replaced by a call on the key() function; if so, generate an appropriate key definition and return the call on key(). If not, return null.
      Parameters:
      pathExp - The path expression to be converted.
      visitor - The expression visitor
      Returns:
      the optimized expression, or null if no optimization is possible
      Throws:
      XPathException
    • tryIndexedFilter

      public Expression tryIndexedFilter(FilterExpression f, ExpressionVisitor visitor, boolean indexFirstOperand)
      Try converting a filter expression to a call on the key function. Return the supplied expression unchanged if not possible
      Parameters:
      f - the filter expression to be converted
      visitor - the expression visitor, which must be currently visiting the filter expression f
      indexFirstOperand - true if the first operand of the filter comparison is to be indexed; false if it is the second operand
      Returns:
      the optimized expression, or the unchanged expression f if no optimization is possible
    • convertToFilterExpression

      public FilterExpression convertToFilterExpression(PathExpression pathExp, TypeHierarchy th) throws XPathException
      Convert a path expression such as a/b/c[predicate] into a filter expression of the form (a/b/c)[predicate]. This is possible whenever the predicate is non-positional. The conversion is useful in the case where the path expression appears inside a loop, where the predicate depends on the loop variable but a/b/c does not.
      Parameters:
      pathExp - the path expression to be converted
      th - the type hierarchy cache
      Returns:
      the resulting filterexpression if conversion is possible, or null if not
      Throws:
      XPathException
    • isIndexableFilter

      public int isIndexableFilter(Expression filter)
      Test whether a filter predicate is indexable.
      Parameters:
      filter - the predicate expression
      Returns:
      0 if not indexable; +1 if the predicate is in the form expression=value; -1 if it is in the form value=expression
    • makeIndexedValue

      public ValueRepresentation makeIndexedValue(SequenceIterator iter) throws XPathException
      Create an indexed value
      Parameters:
      iter - the iterator that delivers the sequence of values to be indexed
      Returns:
      the indexed value
      Throws:
      XPathException
    • isVariableReplaceableByDot

      public boolean isVariableReplaceableByDot(Expression exp, Binding[] binding)
      Determine whether it is possible to rearrange an expression so that all references to a given variable are replaced by a reference to ".". This is true of there are no references to the variable within a filter predicate or on the rhs of a "/" operator.
      Parameters:
      exp - the expression in question
      binding - an array of bindings defining range variables; the method tests that there are no references to any of these variables within a predicate or on the rhs of "/"
      Returns:
      true if the variable reference can be replaced
    • makeConditionalDocumentSorter

      public Expression makeConditionalDocumentSorter(DocumentSorter sorter, PathExpression path)
      Make a conditional document sorter. This optimization is attempted when a DocumentSorter is wrapped around a path expression
      Parameters:
      sorter - the document sorter
      path - the path expression
      Returns:
      the original sorter unchanged when no optimization is possible, which is always the case in Saxon-B
    • tryInlineFunctionCall

      public Expression tryInlineFunctionCall(UserFunctionCall functionCall, ExpressionVisitor visitor, ItemType contextItemType)
      Replace a function call by the body of the function, assuming all conditions for inlining the function are satisfied
      Parameters:
      functionCall - the functionCall expression
      visitor - the expression visitor
      contextItemType - the context item type
      Returns:
      either the original expression unchanged, or an expression that consists of the inlined function body, with all function parameters bound as required. In Saxon-B, function inlining is not supported, so the original functionCall is always returned unchanged
    • promoteExpressionsToGlobal

      public Expression promoteExpressionsToGlobal(Expression body, ExpressionVisitor visitor) throws XPathException
      Identify expressions within a function or template body that can be promoted to be evaluated as global variables.
      Parameters:
      body - the body of the template or function
      visitor - the expression visitor
      Returns:
      the expression after subexpressions have been promoted to global variables
      Throws:
      XPathException
    • trySwitch

      public Expression trySwitch(Choose choose, StaticContext env)
      Try to convert a Choose expression into a switch
      Parameters:
      choose - the Choose expression
      env - the static context
      Returns:
      the result of optimizing this (the original expression if no optimization was possible)
    • extractGlobalVariables

      public Expression extractGlobalVariables(Expression body, ExpressionVisitor visitor) throws XPathException
      Extract subexpressions from the body of a function that can be evaluated as global variables
      Parameters:
      body - the body of the function
      Returns:
      a reference to the new global variable if a variable has been created, or null if not
      Throws:
      XPathException
    • trace

      public void trace(String message, Expression exp)
      Trace optimization actions
      Parameters:
      message - the message to be displayed
      exp - the expression after being rewritten
    • trace

      public void trace(String message)
      Trace optimization actions
      Parameters:
      message - the message to be displayed