The Tor Browser: comparison dom/xslt/xpath/txXPathOptimizer.cpp

--1:000000000000
+:c7e0fdc03a77
+/* -*- 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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comparison: dom/xslt/xpath/txXPathOptimizer.cpp

dom/xslt/xpath/txXPathOptimizer.cpp