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/* -*- 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
#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;
}
}
}