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    41 

    42 //

    43 //  W A R N I N G

    44 //  -------------

    45 //

    46 // This file is not part of the Qt API.  It exists purely as an

    47 // implementation detail.  This header file may change from version to

    48 // version without notice, or even be removed.

    49 //

    50 // We mean it.

    51 

    52 #ifndef Patternist_OptimizerFramework_H

    53 #define Patternist_OptimizerFramework_H

    54 

    55 #include <QSharedData>

    56 

    57 #include "qexpression_p.h"

    58 

    59 QT_BEGIN_HEADER

    60 

    61 QT_BEGIN_NAMESPACE

    62 

    63 namespace QPatternist

    64 {

    65     /**

    66      * @short A factory for creating Expression instances.

    67      *

    68      * ExpressionIdentifier is one of the building block of Patternist's

    69      * optimizer framework. An ExpressionIdentifier sub-class has

    70      * the responsibility of creating the Expression that should be

    71      * the result of the optimization.

    72      *

    73      * This class and sub-classes are never used on their own,

    74      * but in cooperation with OptimizationPass.

    75      *

    76      * @author Frans englich <frans.englich@nokia.com>

    77      * @ingroup Patternist_expressions

    78      */

    79     class ExpressionCreator : public QSharedData

    80     {

    81     public:

    82         typedef QExplicitlySharedDataPointer<ExpressionCreator> Ptr;

    83 

    84         /**

    85          * For some reason this constructor cannot be synthesized.

    86          */

    87         inline ExpressionCreator()

    88         {

    89         }

    90 

    91         virtual ~ExpressionCreator();

    92         /**

    93          * Creates an expression that has @p operands as operands.

    94          *

    95          * The Expression that is returned is guaranteed, by the caller,

    96          * to get a treatment identical to if the expression was created

    97          * in an ordinary compilation(via the parser, and so forth). That is,

    98          * Expression::typeCheck() and Expression::compress() stages will be

    99          * carried out on the returned expression.

   100          *

   101          * @returns an Expression::Ptr that never is non @c null, valid pointer

   102          */

   103         virtual Expression::Ptr create(const Expression::List &operands,

   104                                        const StaticContext::Ptr &context,

   105                                        const SourceLocationReflection *const) const = 0;

   106 

   107     private:

   108         Q_DISABLE_COPY(ExpressionCreator)

   109     };

   110 

   111     /**

   112      * @short Abstract base class for all classes that identify Expressions

   113      * based on some criteria.

   114      *

   115      * ExpressionIdentifier is one of the building block of Patternist's

   116      * optimizer framework. An ExpressionIdentifier sub-class has

   117      * the responsibility of determining whether a particular Expression

   118      * is the one an OptimizationPass should apply for.

   119      *

   120      * This class and sub-classes are never used on their own,

   121      * but in cooperation with OptimizationPass.

   122      *

   123      * @author Frans englich <frans.englich@nokia.com>

   124      * @ingroup Patternist_expressions

   125      */

   126     class ExpressionIdentifier : public QSharedData

   127     {

   128     public:

   129         typedef QExplicitlySharedDataPointer<ExpressionIdentifier> Ptr;

   130         typedef QList<ExpressionIdentifier::Ptr> List;

   131 

   132         /**

   133          * For some reason this constructor cannot be synthesized.

   134          */

   135         inline ExpressionIdentifier()

   136         {

   137         }

   138 

   139         virtual ~ExpressionIdentifier();

   140         /**

   141          * @param expr the Expression to be tested. This is guranteed

   142          * to always be a non @c null, valid pointer.

   143          *

   144          * @returns @c true if @p expr matches as according to this ExpressionIdentifier,

   145          * otherwise @c false.

   146          */

   147         virtual bool matches(const Expression::Ptr &expr) const = 0;

   148 

   149     private:

   150         Q_DISABLE_COPY(ExpressionIdentifier)

   151     };

   152 

   153     /**

   154      * @short Describes how a particular optimization pass should be carried out.

   155      *

   156      * OptimizationPass is essentially a declaration, which describes

   157      * how an optimization pass in the form of an AST rewrite should be done,

   158      * by describing what that should be rewritten into what how.

   159      *

   160      * Each OptimizationPass is applied to a "start" Expression. The Expression

   161      * that qualifies as a start Expression for the OptimizationPass in question is

   162      * determined by startIdentifier; if its ExpressionIdentifier::matches() function

   163      * returns @c true, the optimizer continues to apply this OptimizationPass.

   164      *

   165      * After a start Expression has been found, it is verified if the operands matches

   166      * as well by applying the ExpressionIdentifiers in operandIdentifiers to the

   167      * start Expression's operands. Similarly, if the operands matches what

   168      * operandIdentifiers requires, the optimizer continues to apply this OptimizationPass.

   169      *

   170      * At this stage, it has been concluded that the OptimizationPass validly applies, and

   171      * what now remains is to carry out the actual rewrite. The Expression rewritten

   172      * to is the one returned by ExpressionCreator::create(), when invoked via the resultCreator

   173      * variable.

   174      *

   175      * How these components, startIdentifier, operandIdentifiers, sourceExpression,

   176      * and resultCreator interacts with one another is described in more detail

   177      * in the member documentation as well as the classes they are instances of.

   178      *

   179      * @author Frans englich <frans.englich@nokia.com>

   180      * @ingroup Patternist_expressions

   181      */

   182     class OptimizationPass : public QSharedData

   183     {

   184     public:

   185         typedef QExplicitlySharedDataPointer<OptimizationPass> Ptr;

   186         typedef QList<OptimizationPass::Ptr> List;

   187 

   188         enum OperandsMatchMethod

   189         {

   190             /**

   191              * All operands must match in the same order the ExpressionMarkers do.

   192              */

   193             Sequential = 1,

   194 

   195             /**

   196              * Matches if all operands are matched, regardless of their order. This is

   197              * useful when an OptimizationPass is matching an Expression that has two operands

   198              * and that both of them can appear on the left or right hand as long as it is those

   199              * two.

   200              *

   201              * This comparison method only works when two operands

   202              * needs to be matched.

   203              */

   204             AnyOrder

   205         };

   206 

   207         /**

   208          * An ExpressionMarker identifies an operand Expression relatively

   209          * the start Expression by that each integer identifies a step

   210          * in a descending AST walk. For example an ExpressionMarker with

   211          * only one entry that is 0(zero), identifies the first operand of the

   212          * start Expression. An ExpressionMarker containing 1, 2 in that order

   213          * identifies the third operand of the second operand of the start Expression.

   214          */

   215         typedef QList<qint8> ExpressionMarker;

   216 

   217         /**

   218          * Creates an OptimizationPass and sets its public variables

   219          * to the corresponding values passed in this constructor.

   220          */

   221         OptimizationPass(const ExpressionIdentifier::Ptr &startID,

   222                          const ExpressionIdentifier::List &operandIDs,

   223                          const ExpressionMarker &sourceExpr,

   224                          const ExpressionCreator::Ptr &resultCtor = ExpressionCreator::Ptr(),

   225                          const OperandsMatchMethod matchMethod = Sequential);

   226 

   227         /**

   228          * The ExpressionIdentifier that must the Expression this OptimizationPass concerns.

   229          *

   230          * If this variable is @c null, it means that the start Expression does

   231          * not have to match any particular ExpressionIdentifier, but is fine as is.

   232          *

   233          * One might wonder what the purpose of this startIdentifier is, considering

   234          * that what start Expression an OptimizationPass can at all apply to is

   235          * naturally determined by what Expression::optimizationPasses() re-implementation that

   236          * returns this OptimizationPass. The reason is that in some cases an OptimizationPass

   237          * nevertheless doesn't apply. For example, optimizations applying to a ValueComparison

   238          * might depend on what operator that is in use.

   239          *

   240          * May be @c null or point to an ExpressionIdentifier.

   241          */

   242         const ExpressionIdentifier::Ptr startIdentifier;

   243 

   244         /**

   245          * In order for an OptimizationPass to apply, the start Expression's

   246          * operands must be matched with this list of ExpressionIdentifier instances.

   247          * The first ExpressionIdentifier is applied to the first operand, the second

   248          * ExpressionIdentifier to the second operand, and so forth until all operands

   249          * have been iterated.

   250          *

   251          * Entries in this list may be @c null, and those signals that the corresponding

   252          * operand is not constrained. For example, if the third ExpressionIdentifier in

   253          * the list is @c null, it signals that the third operand may be anykind of expression.

   254          *

   255          * May be empty or contain an arbitrary amount of objects or @c null pointers.

   256          */

   257         const ExpressionIdentifier::List operandIdentifiers;

   258 

   259         /**

   260          * Identifies the expression that should be part of the new expression

   261          * that this OptimizationPass rewrites to. If this list is empty, it

   262          * means that the result is not derived from the existing tree, and

   263          * that resultCreator will exclusively be used for creating the result

   264          * Expression.

   265          *

   266          * How the ExpressionMarker identifies an Expression is document in

   267          * its documentation.

   268          *

   269          * May be empty.

   270          */

   271         const ExpressionMarker sourceExpression;

   272 

   273         /**

   274          * This is the ExpressionCreator that will be used to create the

   275          * Expression which is the result. ExpressionCreator::create()

   276          * will be passed as operands the Expression that sourceExpression

   277          * specify, if any.

   278          *

   279          * If this variable is @c null, the result Expression will be the one

   280          * sourceExpression identifies.

   281          */

   282         const ExpressionCreator::Ptr resultCreator;

   283 

   284         const OperandsMatchMethod operandsMatchMethod;

   285     private:

   286         Q_DISABLE_COPY(OptimizationPass)

   287     };

   288 }

   289 

   290 QT_END_NAMESPACE

   291 

   292 QT_END_HEADER

   293 

   294 #endif