[PATCH] libstdc++: Only call regex_traits::transform_primary() if necessary

[Luca Bacci]

This is both a performance optimization and a partial fix for
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98723.

This commit fixes the issue for bracket expressions that are
not locale-dependant.
---
 libstdc++-v3/include/bits/regex_compiler.tcc | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/regex_compiler.tcc 
b/libstdc++-v3/include/bits/regex_compiler.tcc
index 3c6cb6649df..615ada4e377 100644
--- a/libstdc++-v3/include/bits/regex_compiler.tcc
+++ b/libstdc++-v3/include/bits/regex_compiler.tcc
@@ -608,10 +608,13 @@ 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;
-- 
2.47.0