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| author | Arseny Kapoulkine <arseny.kapoulkine@gmail.com> | 2014-10-27 18:50:09 -0700 |
|---|---|---|
| committer | Arseny Kapoulkine <arseny.kapoulkine@gmail.com> | 2014-10-27 18:50:09 -0700 |
| commit | c64d4820b142e6df93ccf612d0e4717159a36591 (patch) | |
| tree | 67b41215c627fa43283fb1b9a3e14e1bd66fa946 | |
| parent | dbfe85a717b7ac8b9bd30eb51796811c0c651da9 (diff) | |
XPath: Optimize [position()=expr] and [last()]
To get more benefits from constant predicate/filter optimization we rewrite
[position()=expr] predicates into [expr] for numeric expressions. Right now
the rewrite is only for entire expressions - it may be beneficial to split
complex expressions like [position()=constant and expr] into [constant][expr]
but that is more complicated.
last() does not depend on the node set contents so is "constant" as far as
our optimization is concerned so we can evaluate it once.
| -rw-r--r-- | src/pugixml.cpp | 10 | ||||
| -rw-r--r-- | tests/test_xpath_paths.cpp | 8 |
2 files changed, 17 insertions, 1 deletions
diff --git a/src/pugixml.cpp b/src/pugixml.cpp index 67591a3..f0bfc31 100644 --- a/src/pugixml.cpp +++ b/src/pugixml.cpp @@ -9765,6 +9765,14 @@ PUGI__NS_BEGIN if (_right) _right->optimize(alloc); if (_next) _next->optimize(alloc); + // Rewrite [position()=expr] with [expr] + // Note that this step has to go before classification to recognize [position()=1] + if ((_type == ast_filter || _type == ast_predicate) && + _right->_type == ast_op_equal && _right->_left->_type == ast_func_position && _right->_right->_rettype == xpath_type_number) + { + _right = _right->_right; + } + // Classify filter/predicate ops to perform various optimizations during evaluation if (_type == ast_filter || _type == ast_predicate) { @@ -9772,7 +9780,7 @@ PUGI__NS_BEGIN if (_right->_type == ast_number_constant && _right->_data.number == 1.0) _test = predicate_constant_one; - else if (_right->_rettype == xpath_type_number && (_right->_type == ast_number_constant || _right->_type == ast_variable)) + else if (_right->_rettype == xpath_type_number && (_right->_type == ast_number_constant || _right->_type == ast_variable || _right->_type == ast_func_last)) _test = predicate_constant; else if (_right->_rettype != xpath_type_number && _right->is_posinv_expr()) _test = predicate_posinv; diff --git a/tests/test_xpath_paths.cpp b/tests/test_xpath_paths.cpp index 046592a..df0dfa4 100644 --- a/tests/test_xpath_paths.cpp +++ b/tests/test_xpath_paths.cpp @@ -475,6 +475,14 @@ TEST_XML(xpath_paths_predicate_constant_boolean, "<node><chapter/><chapter/><cha CHECK_XPATH_NODESET_VAR(n, STR("following-sibling::chapter[$true]"), &set) % 6 % 7; } +TEST_XML(xpath_paths_predicate_position_eq, "<node><chapter/><chapter/><chapter>3</chapter><chapter/><chapter/></node>") +{ + CHECK_XPATH_NODESET(doc, STR("node/chapter[position()=1]")) % 3; + CHECK_XPATH_NODESET(doc, STR("node/chapter[position()=2+2]")) % 7; + CHECK_XPATH_NODESET(doc, STR("node/chapter[position()=last()]")) % 8; + CHECK_XPATH_NODESET(doc, STR("node/chapter[position()=string()]")) % 5; +} + TEST_XML(xpath_paths_predicate_several, "<node><employee/><employee secretary=''/><employee assistant=''/><employee secretary='' assistant=''/><employee assistant='' secretary=''/></node>") { xml_node n = doc.child(STR("node")); |