diff options
| 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 /src | |
| 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.
Diffstat (limited to 'src')
| -rw-r--r-- | src/pugixml.cpp | 10 |
1 files changed, 9 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; |