The Tor Browser: dom/xslt/xpath/txXPathOptimizer.cpp@b8a032363ba2 (annotated)

dom/xslt/xpath/txXPathOptimizer.cpp@b8a032363ba2 (annotated)

dom/xslt/xpath/txXPathOptimizer.cpp

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "txXPathOptimizer.h"
 #include "txExprResult.h"
 #include "nsIAtom.h"
 #include "nsGkAtoms.h"
 #include "txXPathNode.h"
 #include "txExpr.h"
 #include "txIXPathContext.h"
 class txEarlyEvalContext : public txIEvalContext
 {
 public:
     txEarlyEvalContext(txResultRecycler* aRecycler)
         : mRecycler(aRecycler)
     {
     }
     // txIEvalContext
     nsresult getVariable(int32_t aNamespace, nsIAtom* aLName,
                          txAExprResult*& aResult)
     {
         NS_NOTREACHED("shouldn't depend on this context");
         return NS_ERROR_FAILURE;
     }
     bool isStripSpaceAllowed(const txXPathNode& aNode)
     {
         NS_NOTREACHED("shouldn't depend on this context");
         return false;
     }
     void* getPrivateContext()
     {
         NS_NOTREACHED("shouldn't depend on this context");
         return nullptr;
     }
     txResultRecycler* recycler()
     {
         return mRecycler;
     }
     void receiveError(const nsAString& aMsg, nsresult aRes)
     {
     }
     const txXPathNode& getContextNode()
     {
         NS_NOTREACHED("shouldn't depend on this context");
         // This will return an invalid node, but we should never
         // get here so that's fine.
         return *static_cast<txXPathNode*>(nullptr);
     }
     uint32_t size()
     {
         NS_NOTREACHED("shouldn't depend on this context");
         return 1;
     }
     uint32_t position()
     {
         NS_NOTREACHED("shouldn't depend on this context");
         return 1;
     }
 private:
     txResultRecycler* mRecycler;
 };
 nsresult
 txXPathOptimizer::optimize(Expr* aInExpr, Expr** aOutExpr)
 {
     *aOutExpr = nullptr;
     nsresult rv = NS_OK;
     // First check if the expression will produce the same result
     // under any context.
     Expr::ExprType exprType = aInExpr->getType();
     if (exprType != Expr::LITERAL_EXPR &&
         !aInExpr->isSensitiveTo(Expr::ANY_CONTEXT)) {
         nsRefPtr<txResultRecycler> recycler = new txResultRecycler;
         NS_ENSURE_TRUE(recycler, NS_ERROR_OUT_OF_MEMORY);
         rv = recycler->init();
         NS_ENSURE_SUCCESS(rv, rv);
         txEarlyEvalContext context(recycler);
         nsRefPtr<txAExprResult> exprRes;
         // Don't throw if this fails since it could be that the expression
         // is or contains an error-expression.
         rv = aInExpr->evaluate(&context, getter_AddRefs(exprRes));
         if (NS_SUCCEEDED(rv)) {
             *aOutExpr = new txLiteralExpr(exprRes);
         }
         return NS_OK;
     }
     // Then optimize sub expressions
     uint32_t i = 0;
     Expr* subExpr;
     while ((subExpr = aInExpr->getSubExprAt(i))) {
         Expr* newExpr = nullptr;
         rv = optimize(subExpr, &newExpr);
         NS_ENSURE_SUCCESS(rv, rv);
         if (newExpr) {
             delete subExpr;
             aInExpr->setSubExprAt(i, newExpr);
         }
         ++i;
     }
     // Finally see if current expression can be optimized
     switch (exprType) {
         case Expr::LOCATIONSTEP_EXPR:
             return optimizeStep(aInExpr, aOutExpr);
         case Expr::PATH_EXPR:
             return optimizePath(aInExpr, aOutExpr);
         case Expr::UNION_EXPR:
             return optimizeUnion(aInExpr, aOutExpr);
         default:
             break;
     }
     return NS_OK;
 }
 nsresult
 txXPathOptimizer::optimizeStep(Expr* aInExpr, Expr** aOutExpr)
 {
     LocationStep* step = static_cast<LocationStep*>(aInExpr);
     if (step->getAxisIdentifier() == LocationStep::ATTRIBUTE_AXIS) {
         // Test for @foo type steps.
         txNameTest* nameTest = nullptr;
         if (!step->getSubExprAt(0) &&
             step->getNodeTest()->getType() == txNameTest::NAME_TEST &&
             (nameTest = static_cast<txNameTest*>(step->getNodeTest()))->
                 mLocalName != nsGkAtoms::_asterix) {
             *aOutExpr = new txNamedAttributeStep(nameTest->mNamespace,
                                                  nameTest->mPrefix,
                                                  nameTest->mLocalName);
             NS_ENSURE_TRUE(*aOutExpr, NS_ERROR_OUT_OF_MEMORY);
             return NS_OK; // return since we no longer have a step-object.
         }
     }
     // Test for predicates that can be combined into the nodetest
     Expr* pred;
     while ((pred = step->getSubExprAt(0)) &&
            !pred->canReturnType(Expr::NUMBER_RESULT) &&
            !pred->isSensitiveTo(Expr::NODESET_CONTEXT)) {
         txNodeTest* predTest = new txPredicatedNodeTest(step->getNodeTest(), pred);
         NS_ENSURE_TRUE(predTest, NS_ERROR_OUT_OF_MEMORY);
         step->dropFirst();
         step->setNodeTest(predTest);
     }
     return NS_OK;
 }
 nsresult
 txXPathOptimizer::optimizePath(Expr* aInExpr, Expr** aOutExpr)
 {
     PathExpr* path = static_cast<PathExpr*>(aInExpr);
     uint32_t i;
     Expr* subExpr;
     // look for steps like "//foo" that can be turned into "/descendant::foo"
     // and "//." that can be turned into "/descendant-or-self::node()"
     for (i = 0; (subExpr = path->getSubExprAt(i)); ++i) {
         if (path->getPathOpAt(i) == PathExpr::DESCENDANT_OP &&
             subExpr->getType() == Expr::LOCATIONSTEP_EXPR &&
             !subExpr->getSubExprAt(0)) {
             LocationStep* step = static_cast<LocationStep*>(subExpr);
             if (step->getAxisIdentifier() == LocationStep::CHILD_AXIS) {
                 step->setAxisIdentifier(LocationStep::DESCENDANT_AXIS);
                 path->setPathOpAt(i, PathExpr::RELATIVE_OP);
             }
             else if (step->getAxisIdentifier() == LocationStep::SELF_AXIS) {
                 step->setAxisIdentifier(LocationStep::DESCENDANT_OR_SELF_AXIS);
                 path->setPathOpAt(i, PathExpr::RELATIVE_OP);
             }
         }
     }
     // look for expressions that start with a "./"
     subExpr = path->getSubExprAt(0);
     LocationStep* step;
     if (subExpr->getType() == Expr::LOCATIONSTEP_EXPR &&
         path->getSubExprAt(1) &&
         path->getPathOpAt(1) != PathExpr::DESCENDANT_OP) {
         step = static_cast<LocationStep*>(subExpr);
         if (step->getAxisIdentifier() == LocationStep::SELF_AXIS &&
             !step->getSubExprAt(0)) {
             txNodeTest* test = step->getNodeTest();
             txNodeTypeTest* typeTest;
             if (test->getType() == txNodeTest::NODETYPE_TEST &&
                 (typeTest = static_cast<txNodeTypeTest*>(test))->
                   getNodeTestType() == txNodeTypeTest::NODE_TYPE) {
                 // We have a '.' as first step followed by a single '/'.
                 // Check if there are only two steps. If so, return the second
                 // as resulting expression.
                 if (!path->getSubExprAt(2)) {
                     *aOutExpr = path->getSubExprAt(1);
                     path->setSubExprAt(1, nullptr);
                     return NS_OK;
                 }
                 // Just delete the '.' step and leave the rest of the PathExpr
                 path->deleteExprAt(0);
             }
         }
     }
     return NS_OK;
 }
 nsresult
 txXPathOptimizer::optimizeUnion(Expr* aInExpr, Expr** aOutExpr)
 {
     UnionExpr* uni = static_cast<UnionExpr*>(aInExpr);
     // Check for expressions like "foo | bar" and
     // "descendant::foo | descendant::bar"
     nsresult rv;
     uint32_t current;
     Expr* subExpr;
     for (current = 0; (subExpr = uni->getSubExprAt(current)); ++current) {
         if (subExpr->getType() != Expr::LOCATIONSTEP_EXPR ||
             subExpr->getSubExprAt(0)) {
             continue;
         }
         LocationStep* currentStep = static_cast<LocationStep*>(subExpr);
         LocationStep::LocationStepType axis = currentStep->getAxisIdentifier();
         txUnionNodeTest* unionTest = nullptr;
         // Check if there are any other steps with the same axis and merge
         // them with currentStep
         uint32_t i;
         for (i = current + 1; (subExpr = uni->getSubExprAt(i)); ++i) {
             if (subExpr->getType() != Expr::LOCATIONSTEP_EXPR ||
                 subExpr->getSubExprAt(0)) {
                 continue;
             }
             LocationStep* step = static_cast<LocationStep*>(subExpr);
             if (step->getAxisIdentifier() != axis) {
                 continue;
             }
             // Create a txUnionNodeTest if needed
             if (!unionTest) {
                 nsAutoPtr<txNodeTest> owner(unionTest = new txUnionNodeTest);
                 NS_ENSURE_TRUE(unionTest, NS_ERROR_OUT_OF_MEMORY);
                 rv = unionTest->addNodeTest(currentStep->getNodeTest());
                 NS_ENSURE_SUCCESS(rv, rv);
                 currentStep->setNodeTest(unionTest);
                 owner.forget();
             }
             // Merge the nodetest into the union
             rv = unionTest->addNodeTest(step->getNodeTest());
             NS_ENSURE_SUCCESS(rv, rv);
             step->setNodeTest(nullptr);
             // Remove the step from the UnionExpr
             uni->deleteExprAt(i);
             --i;
         }
         // Check if all expressions were merged into a single step. If so,
         // return the step as the new expression.
         if (unionTest && current == 0 && !uni->getSubExprAt(1)) {
             // Make sure the step doesn't get deleted when the UnionExpr is
             uni->setSubExprAt(0, nullptr);
             *aOutExpr = currentStep;
             // Return right away since we no longer have a union
             return NS_OK;
         }
     }
     return NS_OK;
 }

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dom/xslt/xpath/txXPathOptimizer.cpp@b8a032363ba2 (annotated)

dom/xslt/xpath/txXPathOptimizer.cpp