Package net.sf.saxon.expr.parser

Class Optimizer

java.lang.Object
net.sf.saxon.expr.parser.Optimizer
Direct Known Subclasses:
OptimizerEE
public class Optimizer extends Object
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-HE, which in most cases does no optimization at all: the methods are provided so that they can be overridden in Saxon-EE.

  • Field Details

    • config

      protected Configuration config

    • tracing

      protected boolean tracing

  • 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

    • setOptimizerOptions

      public void setOptimizerOptions(OptimizerOptions options)
      Set the optimizer options
      Parameters:
      options - the optimizer options

    • getOptimizerOptions

      public OptimizerOptions getOptimizerOptions()
      Get the optimizer options
      Returns:
      the optimizer options

    • isOptionSet

      public boolean isOptionSet(int option)
      Ask whether a particular optimizer option is set
      Parameters:
      option - the code identifying the option, e.g. OptimizerOptions.LOOP_LIFTING
      Returns:
      true if the option is set

    • optimizeValueComparison

      public Expression optimizeValueComparison(ValueComparison vc, ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      Optimize a value comparison
      Parameters:
      vc - the value comparison expression
      visitor - the expression visitor
      contextInfo - static context item information
      Returns:
      either the original value comparison, or an optimized equivalent
      Throws:
      XPathException - if things go wrong

    • optimizeGeneralComparison

      public Expression optimizeGeneralComparison(ExpressionVisitor visitor, GeneralComparison gc, boolean backwardsCompatible, ContextItemStaticInfo contextItemType)
      Simplify a GeneralComparison expression
      Parameters:
      visitor - the expression visitor
      gc - the GeneralComparison to be simplified
      backwardsCompatible - true if in 1.0 compatibility mode
      contextItemType - the static type of the context item
      Returns:
      the simplified expression

    • optimizeSaxonStreamFunction

      public Expression optimizeSaxonStreamFunction(ExpressionVisitor visitor, ContextItemStaticInfo cisi, Expression select) throws XPathException
      Attempt to optimize a call on saxon:stream(). Return null if no optimization is possible.
      Parameters:
      visitor - the expression visitor
      cisi - Static information about the context item
      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 - if any error occurs

    • convertPathExpressionToKey

      public Expression convertPathExpressionToKey(SlashExpression pathExp, ExpressionVisitor visitor)
      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

    • tryIndexedFilter

      public Expression tryIndexedFilter(FilterExpression f, ExpressionVisitor visitor, boolean indexFirstOperand, boolean contextIsDoc)
      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
      contextIsDoc - true if the context item is known to be a document node
      Returns:
      the optimized expression, or the unchanged expression f if no optimization is possible

    • reorderPredicates

      public FilterExpression reorderPredicates(FilterExpression f, ExpressionVisitor visitor, ContextItemStaticInfo cisi) throws XPathException
      Consider reordering the predicates in a filter expression based on cost estimates and other criteria
      Parameters:
      f - the filter expression
      visitor - expression visitor
      cisi - information about the context item type
      Returns:
      either the original expression, or an optimized replacement
      Throws:
      XPathException - if things go wrong

    • convertToFilterExpression

      public FilterExpression convertToFilterExpression(SlashExpression pathExp, TypeHierarchy th)
      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 filter expression if conversion is possible, or null if not

    • 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 GroundedValue makeIndexedValue(SequenceIterator iter) throws UnsupportedOperationException, XPathException
      Create an indexed value
      Parameters:
      iter - the iterator that delivers the sequence of values to be indexed
      Returns:
      the indexed value
      Throws:
      UnsupportedOperationException - this method should not be called in Saxon-HE
      XPathException - if an error occurs

    • optimizeNodeSetPattern

      public void optimizeNodeSetPattern(NodeSetPattern pattern)

    • prepareForStreaming

      public void prepareForStreaming(Expression exp) throws XPathException
      Prepare an expression for streaming
      Parameters:
      exp - the expression to be prepared
      Throws:
      XPathException - if any error occurs

    • evaluateStreamingArgument

      public Sequence evaluateStreamingArgument(Expression expr, XPathContext context) throws XPathException
      Evaluate the streaming (first) argument of a streamable stylesheet function
      Parameters:
      expr - the expression supplied for the value of the streaming argument
      context - the XPath evaluation context of the caller
      Returns:
      the (nominal) result of the evaluation
      Throws:
      XPathException - if any error occurs

    • 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, SlashExpression path) throws XPathException
      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-HE
      Throws:
      XPathException - if any error occurs

    • tryInlineFunctionCall

      public Expression tryInlineFunctionCall(UserFunctionCall functionCall, ExpressionVisitor visitor, ContextItemStaticInfo 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-HE, function inlining is not supported, so the original functionCall is always returned unchanged

    • promoteExpressionsToGlobal

      public Expression promoteExpressionsToGlobal(Expression body, GlobalVariableManager gvManager, 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
      gvManager - the global variable manager
      visitor - the expression visitor
      Returns:
      the expression after subexpressions have been promoted to global variables; or null if nothing has changed
      Throws:
      XPathException - if any error occurs

    • eliminateCommonSubexpressions

      public Expression eliminateCommonSubexpressions(Expression in)
      Eliminate common subexpressions. Rewrites (contains(X, 'x') and contains(X, 'y')) as (let $vv:C := X return (contains($vv:C, 'x') and contains($vv:C, 'y'))). Dummy method; the optimization happens only in Saxon-EE.
      Parameters:
      in - the expression to be optimized
      Returns:
      out the optimized expression (possibly the same as the input).

    • trySwitch

      public Expression trySwitch(Choose choose, ExpressionVisitor visitor)
      Try to convert a Choose expression into a switch
      Parameters:
      choose - the Choose expression
      visitor - the expression visitor
      Returns:
      the result of optimizing this (the original expression if no optimization was possible)

    • tryGeneralComparison

      public Expression tryGeneralComparison(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType, OrExpression orExpr) throws XPathException
      Try to convert an Or expression into a comparison with Literal sequence
      Parameters:
      visitor - an expression visitor
      contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
      orExpr - the expression to be converted
      Returns:
      the result of optimizing the Or expression (the original expression if no optimization was possible)
      Throws:
      XPathException - if any error occurs

    • makeInversion

      public RuleTarget makeInversion(Pattern pattern, NamedTemplate template) throws XPathException
      Generate the inversion of the expression comprising the body of a template rules. Supported in Saxon-EE only
      Parameters:
      pattern - the match pattern of this template rule
      template - the template to be inverted
      Returns:
      the inversion of the expression
      Throws:
      XPathException - if any error occurs

    • makeCopyOperationsExplicit

      public void makeCopyOperationsExplicit(Expression parent, Operand child)
      In streaming mode, make the copy operation applied to subexpressions of a complex-content sequence constructor into explicit copy-of operations.
      Parameters:
      parent - the parent expression
      child - the operand

    • checkStreamability

      public void checkStreamability(XSLTemplate sourceTemplate, TemplateRule compiledTemplate) throws XPathException
      Check the streamability of a template
      Parameters:
      sourceTemplate - the source of the template in the stylesheet tree
      compiledTemplate - the compiled template
      Throws:
      XPathException - if the template is declared streamable but does not satisfy the straming rules

    • optimizeForExpressionForStreaming

      public Expression optimizeForExpressionForStreaming(ForExpression expr) throws XPathException
      In streaming mode, optimizer a ForExpression for streaming
      Parameters:
      expr - the expression to be optimized
      Returns:
      the optimized expression
      Throws:
      XPathException - if any error occurs

    • optimizeQuantifiedExpressionForStreaming

      public Expression optimizeQuantifiedExpressionForStreaming(QuantifiedExpression expr) throws XPathException
      In streaming mode, optimizer a QuantifiedExpression for streaming
      Parameters:
      expr - the expression to be optimized
      Returns:
      the optimized expression
      Throws:
      XPathException - if any error occurs

    • generateMultithreadedInstruction

      public Expression generateMultithreadedInstruction(Expression instruction)
      Generate a multi-threaded version of an instruction. Supported in Saxon-EE only; ignored with no action in Saxon-HE and Saxon-PE
      Parameters:
      instruction - the instruction to be multi-threaded
      Returns:
      the multi-threaded version of the instruction

    • optimizeNumberInstruction

      public Expression optimizeNumberInstruction(NumberInstruction ni, ContextItemStaticInfo contextInfo)

    • assessFunctionStreamability

      public void assessFunctionStreamability(XSLFunction reporter, UserFunction compiledFunction) throws XPathException
      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 static void trace(Configuration config, String message, Expression exp)