1 files changed, 256 insertions, 0 deletions
diff --git a/dom/xslt/xpath/txXPathOptimizer.cpp b/dom/xslt/xpath/txXPathOptimizer.cpp
new file mode 100644
index 0000000000..942f54c4b1
--- /dev/null
+++ b/dom/xslt/xpath/txXPathOptimizer.cpp
@@ -0,0 +1,256 @@
+/* -*- 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;
+};
+
+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)) {
+    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.
+    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::_asterisk) {
+      *aOutExpr = new txNamedAttributeStep(
+          nameTest->mNamespace, nameTest->mPrefix, nameTest->mLocalName);
+      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);
+    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();
+      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 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) {
+        UniquePtr<txNodeTest> owner(unionTest = new txUnionNodeTest);
+        rv = unionTest->addNodeTest(currentStep->getNodeTest());
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        currentStep->setNodeTest(unionTest);
+        Unused << owner.release();
+      }
+
+      // 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;
+}