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;
}
