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XPath: Optimize //name queries when possible

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//name means /descendant-or-self::node()/child::name, but we frequently
can replace it with /descendant::name. This means we do not have to build
up a temporary node set with all descendants that can lead to 3x speedups.

git-svn-id: https://pugixml.googlecode.com/svn/trunk@1021 99668b35-9821-0410-8761-19e4c4f06640
This commit is contained in:
Arseny Kapoulkine 2014-09-23 04:39:58 +00:00
parent 89fc7c241c
commit b480523f87
1 changed files with 43 additions and 5 deletions
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48
src/pugixml.cpp
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@ -9328,8 +9328,26 @@ PUGI__NS_BEGIN
return xpath_node_set_raw();
}
}
void optimize()
{
if (_left) _left->optimize();
if (_right) _right->optimize();
if (_next) _next->optimize();
// Replace descendant-or-self::node()/child::foo with descendant::foo
// The former is a full form of //foo, the latter is much faster since it executes the node test immediately
// Note that we only replace positionally invariant steps (//foo[1] != /descendant::foo[1])
if (_type == ast_step && _axis == axis_child && _left &&
_left->_type == ast_step && _left->_axis == axis_descendant_or_self && _left->_test == nodetest_type_node && !_left->_right &&
is_posinv_step())
{
_axis = axis_descendant;
_left = _left->_left;
}
}
bool is_posinv()
bool is_posinv_expr() const
{
switch (_type)
{
@ -9351,15 +9369,33 @@ PUGI__NS_BEGIN
return true;
default:
if (_left && !_left->is_posinv()) return false;
if (_left && !_left->is_posinv_expr()) return false;
for (xpath_ast_node* n = _right; n; n = n->_next)
if (!n->is_posinv()) return false;
if (!n->is_posinv_expr()) return false;
return true;
}
}
bool is_posinv_step() const
{
assert(_type == ast_step);
for (xpath_ast_node* n = _right; n; n = n->_next)
{
assert(n->_type == ast_predicate);
xpath_ast_node* expr = n->_left;
bool posinv = expr->rettype() != xpath_type_number && expr->is_posinv_expr();
if (!posinv)
return false;
}
return true;
}
xpath_value_type rettype() const
{
return static_cast<xpath_value_type>(_rettype);
@ -9773,7 +9809,7 @@ PUGI__NS_BEGIN
if (n->rettype() != xpath_type_node_set) throw_error("Predicate has to be applied to node set");
bool posinv = expr->rettype() != xpath_type_number && expr->is_posinv();
bool posinv = expr->rettype() != xpath_type_number && expr->is_posinv_expr();
n = new (alloc_node()) xpath_ast_node(posinv ? ast_filter_posinv : ast_filter, xpath_type_node_set, n, expr);
@ -9930,7 +9966,7 @@ PUGI__NS_BEGIN
last = pred;
}
return n;
}
@ -10663,6 +10699,8 @@ namespace pugi
if (qimpl->root)
{
qimpl->root->optimize();
_impl = static_cast<impl::xpath_query_impl*>(impl_holder.release());
_result.error = 0;
}