Reduce code instantiated by filesystem::path::_S_convert_loc

Jakub noted in https://gcc.gnu.org/ml/libstdc++/2019-04/msg00140.html
that an unwanted std::wstring::_M_replace_dispatch symbol has started to
be exported from the Fedora shared library. This symbol is triggered by
the instantiation of std::wstring::assign(const char*, const char*) from
std::__str_codecvt_in which is called from path::_S_convert_loc. The
branch that triggers that instantiation can't actually happen in that
case, because codecvt facets will only return noconv when the input and
output types are the same. Guarding the assign call with an if-constexpr
check that the types are the same avoids instantiating template
specializations that will never actually be needed.

Backport from mainline
2019-04-26  Jonathan Wakely  <jwakely@redhat.com>

	* config/abi/pre/gnu.ver (GLIBCXX_3.4): Replace wildcard that matches
	wstring::_M_replace_dispatch with more specific patterns.
	* include/bits/fs_path.h (path::_S_convert_loc<_InputIterator>):
	Create const std::string to avoid redundant call to _S_convert_loc
	with non-const pointers.
	* include/bits/locale_conv.h (__do_str_codecvt): Use if-constexpr to
	avoid unnecessary basic_string::assign instantiations.

From-SVN: r272306

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 1f503c40fe89cb49e6301db6c945d77a2893ece2..e9ed7eaefd3735cbe3766f846f98a3f045e95ac8 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,16 @@
+2019-06-14  Jonathan Wakely  <jwakely@redhat.com>
+
+       Backport from mainline
+       2019-04-26  Jonathan Wakely  <jwakely@redhat.com>
+
+       * config/abi/pre/gnu.ver (GLIBCXX_3.4): Replace wildcard that matches
+       wstring::_M_replace_dispatch with more specific patterns.
+       * include/bits/fs_path.h (path::_S_convert_loc<_InputIterator>):
+       Create const std::string to avoid redundant call to _S_convert_loc
+       with non-const pointers.
+       * include/bits/locale_conv.h (__do_str_codecvt): Use if-constexpr to
+       avoid unnecessary basic_string::assign instantiations.
+
 2019-06-14  Jonathan Wakely  <jwakely@redhat.com>
 
        Backport from mainline

diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h
index ecef19e361bef28c36fd1f18b74f1d802ab6988b..0e07e232d1e1ee65a15d0c665c3f71f51253dc82 100644 (file)
--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -539,7 +539,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       _S_convert_loc(_InputIterator __src, __null_terminated,
                     const std::locale& __loc)
       {
-       std::string __s = _S_string_from_iter(__src);
+       const std::string __s = _S_string_from_iter(__src);
        return _S_convert_loc(__s.data(), __s.data() + __s.size(), __loc);
       }
 

diff --git a/libstdc++-v3/include/bits/locale_conv.h b/libstdc++-v3/include/bits/locale_conv.h
index d7510dff80e4c5f8d156d54dbf8c76f4349c7ac1..4cb9c39ebb46c8d36362079edd9e2a5d5bda461d 100644 (file)
--- a/libstdc++-v3/include/bits/locale_conv.h
+++ b/libstdc++-v3/include/bits/locale_conv.h
@@ -88,8 +88,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       if (__result == codecvt_base::noconv)
        {
-         __outstr.assign(__first, __last);
-         __count = __last - __first;
+         // The codecvt facet will only return noconv when the types are
+         // the same, so avoid instantiating basic_string::assign otherwise
+         if _GLIBCXX17_CONSTEXPR (is_same<typename _Codecvt::intern_type,
+                                          typename _Codecvt::extern_type>())
+           {
+             __outstr.assign(__first, __last);
+             __count = __last - __first;
+           }
        }
       else
        {