From c64d4820b142e6df93ccf612d0e4717159a36591 Mon Sep 17 00:00:00 2001 From: Arseny Kapoulkine Date: Mon, 27 Oct 2014 18:50:09 -0700 Subject: 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. --- src/pugixml.cpp | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'src/pugixml.cpp') 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; -- cgit v1.2.3