commit c435fd7ed919ae54fc8f730844c7466822787ff8
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Sep 11 17:29:34 2017 +0100

    Adjust test to pass with old std::string
    
            * testsuite/21_strings/basic_string/lwg2946.cc: Adjust for
            compatibility with old COW std::string.

diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/lwg2946.cc b/libstdc++-v3/testsuite/21_strings/basic_string/lwg2946.cc
index 74d5a5c89a7..fe1f15553fb 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/lwg2946.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/lwg2946.cc
@@ -29,7 +29,7 @@ int main()
   s.assign({"abc", 1});
   s.insert(0, {"abc", 1});
   s.replace(0, 1, {"abc", 1});
-  s.replace(s.cbegin(), s.cbegin(), {"abc", 1});
+  s.replace(s.begin(), s.begin(), {"abc", 1});
   s.find({"abc", 1});
   s.rfind({"abc", 1});
   s.find_first_of({"abc", 1});