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-rw-r--r--dom/xslt/xpath/txXPathOptimizer.cpp246
1 files changed, 246 insertions, 0 deletions
diff --git a/dom/xslt/xpath/txXPathOptimizer.cpp b/dom/xslt/xpath/txXPathOptimizer.cpp
new file mode 100644
index 0000000000..40a94f674c
--- /dev/null
+++ b/dom/xslt/xpath/txXPathOptimizer.cpp
@@ -0,0 +1,246 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 "mozilla/Assertions.h"
+#include "txXPathOptimizer.h"
+#include "txExprResult.h"
+#include "nsAtom.h"
+#include "nsGkAtoms.h"
+#include "txXPathNode.h"
+#include "txExpr.h"
+#include "txIXPathContext.h"
+
+using mozilla::UniquePtr;
+using mozilla::Unused;
+
+class txEarlyEvalContext : public txIEvalContext {
+ public:
+ explicit txEarlyEvalContext(txResultRecycler* aRecycler)
+ : mRecycler(aRecycler) {}
+
+ // txIEvalContext
+ nsresult getVariable(int32_t aNamespace, nsAtom* aLName,
+ txAExprResult*& aResult) override {
+ MOZ_CRASH("shouldn't depend on this context");
+ }
+ nsresult isStripSpaceAllowed(const txXPathNode& aNode,
+ bool& aAllowed) override {
+ MOZ_CRASH("shouldn't depend on this context");
+ }
+ void* getPrivateContext() override {
+ MOZ_CRASH("shouldn't depend on this context");
+ }
+ txResultRecycler* recycler() override { return mRecycler; }
+ void receiveError(const nsAString& aMsg, nsresult aRes) override {}
+ const txXPathNode& getContextNode() override {
+ MOZ_CRASH("shouldn't depend on this context");
+ }
+ uint32_t size() override { MOZ_CRASH("shouldn't depend on this context"); }
+ uint32_t position() override {
+ MOZ_CRASH("shouldn't depend on this context");
+ }
+
+ private:
+ txResultRecycler* mRecycler;
+};
+
+void txXPathOptimizer::optimize(Expr* aInExpr, Expr** aOutExpr) {
+ *aOutExpr = nullptr;
+
+ // 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)) {
+ RefPtr<txResultRecycler> recycler = new txResultRecycler;
+ txEarlyEvalContext context(recycler);
+ RefPtr<txAExprResult> exprRes;
+
+ // Don't throw if this fails since it could be that the expression
+ // is or contains an error-expression.
+ nsresult rv = aInExpr->evaluate(&context, getter_AddRefs(exprRes));
+ if (NS_SUCCEEDED(rv)) {
+ *aOutExpr = new txLiteralExpr(exprRes);
+ }
+
+ return;
+ }
+
+ // Then optimize sub expressions
+ uint32_t i = 0;
+ Expr* subExpr;
+ while ((subExpr = aInExpr->getSubExprAt(i))) {
+ Expr* newExpr = nullptr;
+ optimize(subExpr, &newExpr);
+ if (newExpr) {
+ delete subExpr;
+ aInExpr->setSubExprAt(i, newExpr);
+ }
+
+ ++i;
+ }
+
+ // Finally see if current expression can be optimized
+ switch (exprType) {
+ case Expr::LOCATIONSTEP_EXPR:
+ optimizeStep(aInExpr, aOutExpr);
+ return;
+
+ case Expr::PATH_EXPR:
+ optimizePath(aInExpr, aOutExpr);
+ return;
+
+ case Expr::UNION_EXPR:
+ optimizeUnion(aInExpr, aOutExpr);
+ return;
+
+ default:
+ return;
+ }
+}
+
+void 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::_asterisk) {
+ *aOutExpr = new txNamedAttributeStep(
+ nameTest->mNamespace, nameTest->mPrefix, nameTest->mLocalName);
+ return; // 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);
+ step->dropFirst();
+ step->setNodeTest(predTest);
+ }
+}
+
+void 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();
+ if (test->getType() == txNodeTest::NODETYPE_TEST &&
+ (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;
+ }
+
+ // Just delete the '.' step and leave the rest of the PathExpr
+ path->deleteExprAt(0);
+ }
+ }
+ }
+}
+
+void txXPathOptimizer::optimizeUnion(Expr* aInExpr, Expr** aOutExpr) {
+ UnionExpr* uni = static_cast<UnionExpr*>(aInExpr);
+
+ // Check for expressions like "foo | bar" and
+ // "descendant::foo | descendant::bar"
+
+ 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) {
+ UniquePtr<txNodeTest> owner(unionTest = new txUnionNodeTest);
+ unionTest->addNodeTest(currentStep->getNodeTest());
+
+ currentStep->setNodeTest(unionTest);
+ Unused << owner.release();
+ }
+
+ // Merge the nodetest into the union
+ unionTest->addNodeTest(step->getNodeTest());
+
+ 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;
+ }
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-19 16:17:11 +0000