libstdc++: Call regex_traits::transform_primary() only when necessary [PR98723]

This is both a performance optimization and a partial fix for PR 98723.

This commit fixes the issue for bracket expressions that do not depend
on the locale's collation facet. Examples:

 * Character ranges ([a-z]) when std::regex::collate is not set
 * Character classes ([:alnum:])
 * Individual characters ([abc])

Signed-off-by: Luca Bacci <luca.bacci982@gmail.com>
libstdc++-v3/ChangeLog:

	PR libstdc++/98723
	* include/bits/regex_compiler.tcc (_BracketMatcher::_M_apply):
	Only use transform_primary when an equivalence set is used.

diff --git a/libstdc++-v3/include/bits/regex_compiler.tcc b/libstdc++-v3/include/bits/regex_compiler.tcc
index 9c5a46a47cd08139d3ee60f6e3f59e221af3cd49..5037195ca17af92d3b27b92632b2c95e822e6d3f 100644 (file)
--- a/libstdc++-v3/include/bits/regex_compiler.tcc
+++ b/libstdc++-v3/include/bits/regex_compiler.tcc
@@ -611,10 +611,13 @@ namespace __detail
            return true;
        if (_M_traits.isctype(__ch, _M_class_set))
          return true;
-       if (std::find(_M_equiv_set.begin(), _M_equiv_set.end(),
-                     _M_traits.transform_primary(&__ch, &__ch+1))
-           != _M_equiv_set.end())
-         return true;
+       if (!_M_equiv_set.empty())
+         {
+           auto __x = _M_traits.transform_primary(&__ch, &__ch+1);
+           auto __p = std::find(_M_equiv_set.begin(), _M_equiv_set.end(), __x);
+           if (__p != _M_equiv_set.end())
+             return true;
+         }
        for (auto& __it : _M_neg_class_set)
          if (!_M_traits.isctype(__ch, __it))
            return true;