com.saxonica.extra
Class OptimizerSA

java.lang.Object
  extended by net.sf.saxon.expr.Optimizer
      extended by com.saxonica.extra.OptimizerSA
All Implemented Interfaces:
Serializable

public class OptimizerSA
extends Optimizer

This class doesn't actually do any optimization itself, despite the name. Rather, it is intended to act as a factory for implementation classes that perform optimization, so that the appropriate level of optimization can be selected.

See Also:
Serialized Form

Constructor Summary
OptimizerSA(Configuration config)
          Create the Saxon-SA 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)
          Extract subexpressions from the body of a function that can be evaluated as global variables
 int isIndexableFilter(Expression filter)
          Test whether a filter predicate is indexable.
 Value makeClosure(Expression expression, int ref, XPathContext context)
          Make a Closure, given the expected reference count
 Expression makeConditionalDocumentSorter(DocumentSorter sorter, PathExpression path)
          Make a conditional document sorter.
 BinaryExpression makeGeneralComparison(Expression p0, int op, Expression p1, boolean backwardsCompatible)
          Create a GeneralComparison expression
 ValueRepresentation makeIndexedValue(SequenceIterator iter)
          Create an indexed value
 ValueRepresentation makeSequenceExtent(Expression expression, int ref, XPathContext context)
          Make a SequenceExtent, given the expected reference count
 Expression optimizeCopy(Expression select)
          Attempt to optimize a copy operation.
 Expression optimizeStreamingCopy(Expression select)
          Given a select expression, determine whether it is a candidate for sequential processing, and if so, return a SequentialCopy expression that does the work.
 Expression promoteExpressionsToGlobal(Expression body, ExpressionVisitor visitor)
          Identify expressions within a function or template body that can be promoted to be evaluated as global variables.
 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 net.sf.saxon.expr.Optimizer
getConfiguration, trace, trace
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

OptimizerSA

public OptimizerSA(Configuration config)
Create the Saxon-SA optimizer

Parameters:
config - the Saxon-SA configuration
Method Detail

makeGeneralComparison

public BinaryExpression makeGeneralComparison(Expression p0,
                                              int op,
                                              Expression p1,
                                              boolean backwardsCompatible)
Create a GeneralComparison expression

Overrides:
makeGeneralComparison in class Optimizer
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.

Overrides:
optimizeCopy in class Optimizer
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

optimizeStreamingCopy

public Expression optimizeStreamingCopy(Expression select)
                                 throws XPathException
Given a select expression, determine whether it is a candidate for sequential processing, and if so, return a SequentialCopy expression that does the work.

To qualify, the select expression must be a path expression that starts with a call on doc() or document(), and whose subsequent steps are all axis steps using the child, descendant, and attribute axes only; there must be no predicates; it must match either elements only, or attributes only

Parameters:
select - the select expression to be examined
Returns:
either null if no optimization is possible, or a StreamingCopy expression
Throws:
XPathException

makeClosure

public Value makeClosure(Expression expression,
                         int ref,
                         XPathContext context)
                  throws XPathException
Make a Closure, given the expected reference count

Overrides:
makeClosure in class Optimizer
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

Overrides:
makeSequenceExtent in class Optimizer
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.

Overrides:
convertPathExpressionToKey in class Optimizer
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

Overrides:
tryIndexedFilter in class Optimizer
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.

Overrides:
convertToFilterExpression in class Optimizer
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.

Overrides:
isIndexableFilter in class Optimizer
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

Overrides:
makeIndexedValue in class Optimizer
Parameters:
iter - the iterator that delivers the sequence of values to be indexed
Returns:
the indexed value
Throws:
XPathException

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

Overrides:
makeConditionalDocumentSorter in class Optimizer
Parameters:
sorter - an expression that sorts and deduplicates its operand
path - the path expression that is the operand of the sorter
Returns:
either the original sorter, if no optimization is possible; or a ConditionalSorter which first tests a condition, and performs the sort if the condition is true, or returns the unsorted operand if not. In practice the condition is always a test whether the first item in the path expression contains more than one item

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

Overrides:
tryInlineFunctionCall in class Optimizer
Parameters:
functionCall - the functionCall expression
visitor - the expression visitor
contextItemType - the static type of the context item
Returns:
either the original expression unchanged, or an expression that consists of the inlined function body, with all function parameters bound as required.

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.

Overrides:
promoteExpressionsToGlobal in class Optimizer
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

Overrides:
trySwitch in class Optimizer
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

Overrides:
extractGlobalVariables in class Optimizer
Parameters:
body - an expression with no dependencies other than on global variables (already checked by the caller)
Returns:
a reference to the new global variable if a variable has been created, or null if not
Throws:
XPathException


Copyright (C) Michael H. Kay. All rights reserved.