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## net.sf.saxon.expr
Class Optimizer

    java.lang.Object
      net.sf.saxon.expr.Optimizer

All Implemented Interfaces:
  Serializable

Direct Known Subclasses:
  OptimizerEE

    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-EE.

See Also:
  Serialized Form

Field Summary
`protected Configuration` | `config`
`static int` | `FULL_OPTIMIZATION`
`static int` | `NO_OPTIMIZATION`

Constructor Summary
`Optimizer(Configuration config)` Create an Optimizer.

Method Summary
`Expression` | `convertPathExpressionToKey(PathExpression 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().
`FilterExpression` | `convertToFilterExpression(PathExpression pathExp, TypeHierarchy th)` Convert a path expression such as a/b/c[predicate] into a filter expression of the form (a/b/c)[predicate].
`Expression` | `extractGlobalVariables(Expression body, ExpressionVisitor visitor, PromotionOffer offer)` Extract subexpressions from the body of a function that can be evaluated as global variables
`Expression` | `generateMultithreadedInstruction(Expression instruction)` Generate a multi-threaded version of an instruction.
`Configuration` | `getConfiguration()` Get the Saxon configuration object
`int` | `getOptimizationLevel()` Get the optimization level
`int` | `isIndexableFilter(Expression filter)` Test whether a filter predicate is indexable.
`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 ".".
`Expression` | `makeConditionalDocumentSorter(DocumentSorter sorter, PathExpression path)` Make a conditional document sorter.
`void` | `makeCopyOperationsExplicit(Expression parent, Expression child)` In streaming mode, make the copy operation applied to subexpressions of a complex-content sequence constructor into explicit copy-of operations.
`ValueRepresentation` | `makeIndexedValue(SequenceIterator iter)` Create an indexed value
`RuleTarget` | `makeInversion(Pattern pattern, Template template, NodeTest nodeTest)` Generate the inversion of the expression comprising the body of a template rules.
`Expression` | `makeStreamingApplyTemplates(ApplyTemplates inst)` Make a streaming applyTemplates instruction.
`Expression` | `optimizeCopy(Expression select)` Attempt to optimize a copy operation.
`Expression` | `optimizeForExpressionForStreaming(ForExpression expr)` In streaming mode, optimizer a ForExpression for streaming
`Expression` | `optimizeQuantifiedExpressionForStreaming(QuantifiedExpression expr)` In streaming mode, optimizer a QuantifiedExpression for streaming
`Expression` | `promoteExpressionsToGlobal(Expression body, ExpressionVisitor visitor)` Identify expressions within a function or template body that can be promoted to be evaluated as global variables.
`void` | `setOptimizationLevel(int level)` Set the optimization level
`BinaryExpression` | `simplifyGeneralComparison(GeneralComparison gc, boolean backwardsCompatible)` Simplify a GeneralComparison expression
`void` | `trace(String message)` Trace optimization actions
`void` | `trace(String message, Expression exp)` Trace optimization actions
`Expression` | `tryIndexedFilter(FilterExpression f, ExpressionVisitor visitor, boolean indexFirstOperand)` Try converting a filter expression to a call on the key function.
`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
`Expression` | `trySwitch(Choose choose, StaticContext env)` Try to convert a Choose expression into a switch

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### NO_OPTIMIZATION

    public static final int NO_OPTIMIZATION

See Also:
  Constant Field Values

### FULL_OPTIMIZATION

    public static final int FULL_OPTIMIZATION

See Also:
  Constant Field Values

### config

    protected Configuration config

Constructor Detail

### Optimizer

    public Optimizer(Configuration config)

  Create an Optimizer.

  Parameters:
    `config` - the Saxon configuration

Method Detail

### getConfiguration

    public Configuration getConfiguration()

  Get the Saxon configuration object

  Returns:
    the configuration

### setOptimizationLevel

    public void setOptimizationLevel(int level)

  Set the optimization level

  Parameters:
    `level` - the optimization level, between 0 (no optimization) and 10 (full optimization). Currently all values greater than zero have the same effect as full optimization

### getOptimizationLevel

    public int getOptimizationLevel()

  Get the optimization level

  Returns:
    the optimization level, between 0 (no optimization) and 10 (full optimization). Currently all values greater than zero have the same effect as full optimization

### simplifyGeneralComparison

    public BinaryExpression simplifyGeneralComparison(GeneralComparison gc,
                                                      boolean backwardsCompatible)

  Simplify a GeneralComparison expression

  Parameters:
    `gc` - the GeneralComparison to be simplified
    `backwardsCompatible` - true if in 1.0 compatibility mode
  Returns:
    the simplified 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`

### 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:
    `UnsupportedOperationException:` - this method should not be called in Saxon-B
    `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; or null if nothing has changed
  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,
                                             PromotionOffer offer)
                                      throws XPathException

  Extract subexpressions from the body of a function that can be evaluated as global variables

  Parameters:
    `body` - the body of the function
    `offer` - The PromotionOffer. Will be marked to indicate whether any action was taken
  Returns:
    a reference to the new global variable if a variable has been created, or null if not
  Throws:
    `XPathException`

### makeStreamingApplyTemplates

    public Expression makeStreamingApplyTemplates(ApplyTemplates inst)
                                           throws XPathException

  Make a streaming applyTemplates instruction. Supported in Saxon-EE only

  Parameters:
    `inst` - the unoptimized applyTemplates instruction
  Throws:
    `XPathException`

### makeInversion

    public RuleTarget makeInversion(Pattern pattern,
                                    Template template,
                                    NodeTest nodeTest)
                             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
    `nodeTest` - the static item type of the context node of the template
  Throws:
    `XPathException`

### makeCopyOperationsExplicit

    public void makeCopyOperationsExplicit(Expression parent,
                                           Expression child)
                                    throws XPathException

  In streaming mode, make the copy operation applied to subexpressions of a complex-content sequence constructor into explicit copy-of operations.

  Throws:
    `XPathException`

### 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`

### 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`

### 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

### 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

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