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XPath: Extend the descendant-or-self optimization

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Use descendant-or-self::node() transformation for self, descendant and
descendant-or-self axis. Self axis should be semi-frequent; descendant
axes should not really be used with // but if they ever are the complexity
of the step becomes quadratic so it's better to optimize this if possible.

git-svn-id: https://pugixml.googlecode.com/svn/trunk@1063 99668b35-9821-0410-8761-19e4c4f06640
This commit is contained in:
Arseny Kapoulkine 2014-10-18 15:28:02 +00:00
parent 45e0c726f0
commit 72ec01c5f6
2 changed files with 22 additions and 2 deletions
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9
src/pugixml.cpp
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@ -9613,12 +9613,17 @@ PUGI__NS_BEGIN
// 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
// Do a similar kind of replacement for self/descendant/descendant-or-self axes
// Note that we only replace positionally invariant steps (//foo[1] != /descendant::foo[1])
if (_type == ast_step && _axis == axis_child && _left &&
if (_type == ast_step && (_axis == axis_child || _axis == axis_self || _axis == axis_descendant || _axis == axis_descendant_or_self) && _left &&
_left->_type == ast_step && _left->_axis == axis_descendant_or_self && _left->_test == nodetest_type_node && !_left->_right &&
is_posinv_step())
{
_axis = axis_descendant;
if (_axis == axis_child || _axis == axis_descendant)
_axis = axis_descendant;
else
_axis = axis_descendant_or_self;
_left = _left->_left;
}

15
tests/test_xpath_paths.cpp
View file

@ -531,6 +531,21 @@ TEST_XML(xpath_paths_descendant_optimize, "<node><para><para/><para/><para><para
CHECK_XPATH_NODESET(doc, STR("/descendant-or-self::node()[3]/child::para")) % 4 % 5 % 6;
}
TEST_XML(xpath_paths_descendant_optimize_axes, "<node><para><para/><para/><para><para/></para></para><para/></node>")
{
CHECK_XPATH_NODESET(doc, STR("//.")) % 1 % 2 % 3 % 4 % 5 % 6 % 7 % 8;
CHECK_XPATH_NODESET(doc, STR("//descendant::*")) % 2 % 3 % 4 % 5 % 6 % 7 % 8;
CHECK_XPATH_NODESET(doc, STR("//descendant-or-self::*")) % 2 % 3 % 4 % 5 % 6 % 7 % 8;
CHECK_XPATH_NODESET(doc, STR("//..")) % 1 % 2 % 3 % 6;
CHECK_XPATH_NODESET(doc, STR("//ancestor::*")) % 2 % 3 % 6;
CHECK_XPATH_NODESET(doc, STR("//ancestor-or-self::*")) % 2 % 3 % 4 % 5 % 6 % 7 % 8;
CHECK_XPATH_NODESET(doc, STR("//preceding-sibling::*")) % 3 % 4 % 5;
CHECK_XPATH_NODESET(doc, STR("//following-sibling::*")) % 5 % 6 % 8;
CHECK_XPATH_NODESET(doc, STR("//preceding::*")) % 3 % 4 % 5 % 6 % 7;
CHECK_XPATH_NODESET(doc, STR("//following::*")) % 5 % 6 % 7 % 8;
}
TEST_XML(xpath_paths_descendant_optimize_last, "<node><para><para/><para/><para><para/></para></para><para/></node>")
{
CHECK_XPATH_NODESET(doc, STR("//para[last()]")) % 6 % 7 % 8;