[PATCH] PR libstdc++/86450 use -Wabi=2 and simplify -Werror use

[Jonathan Wakely]

Use -Wabi=2 to fix warnings about -Wabi having no effect on its own.
This requires suppressing two warnings in src/c++11/debug.cc which do
not affect the library ABI.

Previously libstdc++ defaulted to --enable-werror but the -Werror flag
was not actually added unless --enable-maintainer-mode was used. This is
not documented and not the expected behaviour. This removes any special
treatment for maintainer-mode, makes -Werror depend directly on
--enable-werror, and changes the default to --enable-werror=no.

	PR libstdc++/86450
	* acinclude.m4 (GLIBCXX_CHECK_COMPILER_FEATURES): Don't define WERROR.
	(GLIBCXX_EXPORT_FLAGS): Use -Wabi=2 instead of -Wabi.
	* configure: Regenerate.
	* configure.ac: Change GLIBCXX_ENABLE_WERROR default to "no".
	* doc/Makefile.in: Regenerate.
	* fragment.am: Set WERROR_FLAG to -Werror instead of $(WERROR).
	* include/Makefile.in: Regenerate.
	* libsupc++/Makefile.in: Regenerate.
	* po/Makefile.in: Regenerate.
	* python/Makefile.in: Regenerate.
	* src/Makefile.in: Regenerate.
	* src/c++11/Makefile.in: Regenerate.
	* src/c++11/debug.cc: Use diagnostic pragmas to suppress warnings
	from -Wabi=2 that don't affect exported symbols.
	* src/c++98/Makefile.in: Regenerate.
	* src/filesystem/Makefile.in: Regenerate.
	* testsuite/Makefile.in: Regenerate.

Tested powerpc64le-linux, committed to trunk.


-------------- next part --------------
commit 0e99fd82ce20499c4da0d0950e7197f14d45311f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jul 17 00:59:17 2018 +0100

    PR libstdc++/86450 use -Wabi=2 and simplify -Werror use
    
    Use -Wabi=2 to fix warnings about -Wabi having no effect on its own.
    This requires suppressing two warnings in src/c++11/debug.cc which do
    not affect the library ABI.
    
    Previously libstdc++ defaulted to --enable-werror but the -Werror flag
    was not actually added unless --enable-maintainer-mode was used. This is
    not documented and not the expected behaviour. This removes any special
    treatment for maintainer-mode, makes -Werror depend directly on
    --enable-werror, and changes the default to --enable-werror=no.
    
            PR libstdc++/86450
            * acinclude.m4 (GLIBCXX_CHECK_COMPILER_FEATURES): Don't define WERROR.
            (GLIBCXX_EXPORT_FLAGS): Use -Wabi=2 instead of -Wabi.
            * configure: Regenerate.
            * configure.ac: Change GLIBCXX_ENABLE_WERROR default to "no".
            * doc/Makefile.in: Regenerate.
            * fragment.am: Set WERROR_FLAG to -Werror instead of $(WERROR).
            * include/Makefile.in: Regenerate.
            * libsupc++/Makefile.in: Regenerate.
            * po/Makefile.in: Regenerate.
            * python/Makefile.in: Regenerate.
            * src/Makefile.in: Regenerate.
            * src/c++11/Makefile.in: Regenerate.
            * src/c++11/debug.cc: Use diagnostic pragmas to suppress warnings
            from -Wabi=2 that don't affect exported symbols.
            * src/c++98/Makefile.in: Regenerate.
            * src/filesystem/Makefile.in: Regenerate.
            * testsuite/Makefile.in: Regenerate.

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index cf5add167e6..bbf3c8df3e1 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -140,13 +140,6 @@ AC_DEFUN([GLIBCXX_CHECK_COMPILER_FEATURES], [
   ac_test_CXXFLAGS="${CXXFLAGS+set}"
   ac_save_CXXFLAGS="$CXXFLAGS"
 
-  # Check for maintainer-mode bits.
-  if test x"$USE_MAINTAINER_MODE" = xno; then
-    WERROR=''
-  else
-    WERROR='-Werror'
-  fi
-
   # Check for -ffunction-sections -fdata-sections
   AC_MSG_CHECKING([for g++ that supports -ffunction-sections -fdata-sections])
   CXXFLAGS='-g -Werror -ffunction-sections -fdata-sections'
@@ -163,7 +156,6 @@ AC_DEFUN([GLIBCXX_CHECK_COMPILER_FEATURES], [
   AC_MSG_RESULT($ac_fdsections)
 
   AC_LANG_RESTORE
-  AC_SUBST(WERROR)
   AC_SUBST(SECTION_FLAGS)
 ])
 
@@ -733,7 +725,7 @@ AC_DEFUN([GLIBCXX_EXPORT_FLAGS], [
   # OPTIMIZE_CXXFLAGS = -O3 -fstrict-aliasing -fvtable-gc
   AC_SUBST(OPTIMIZE_CXXFLAGS)
 
-  WARN_FLAGS='-Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi'
+  WARN_FLAGS="-Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi=2"
   AC_SUBST(WARN_FLAGS)
 ])
 
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index 7e1fd84606a..1e0a33fb3ea 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -175,7 +175,7 @@ GLIBCXX_ENABLE_CXX_FLAGS
 GLIBCXX_ENABLE_FULLY_DYNAMIC_STRING([no])
 GLIBCXX_ENABLE_EXTERN_TEMPLATE([yes])
 GLIBCXX_ENABLE_PYTHON
-GLIBCXX_ENABLE_WERROR([yes])
+GLIBCXX_ENABLE_WERROR([no])
 GLIBCXX_ENABLE_VTABLE_VERIFY([no])
 
 # Checks for operating systems support that doesn't require linking.
diff --git a/libstdc++-v3/fragment.am b/libstdc++-v3/fragment.am
index 898569520b9..216c572fc60 100644
--- a/libstdc++-v3/fragment.am
+++ b/libstdc++-v3/fragment.am
@@ -14,9 +14,9 @@ toolexecdir = $(glibcxx_toolexecdir)
 toolexeclibdir = $(glibcxx_toolexeclibdir)
 
 if ENABLE_WERROR
-WERROR_FLAG=$(WERROR)
+WERROR_FLAG = -Werror
 else
-WERROR_FLAG=
+WERROR_FLAG =
 endif
 
 if ENABLE_EXTERN_TEMPLATE
diff --git a/libstdc++-v3/src/c++11/debug.cc b/libstdc++-v3/src/c++11/debug.cc
index cb64dd9240e..88fe889dd6a 100644
--- a/libstdc++-v3/src/c++11/debug.cc
+++ b/libstdc++-v3/src/c++11/debug.cc
@@ -66,6 +66,10 @@ namespace
     return __gnu_internal::get_mutex(index);
   }
 
+#pragma GCC diagnostic push
+// Suppress -Wabi=2 warnings due to PR c++/51322 mangling change
+#pragma GCC diagnostic warning "-Wabi=6"
+
   void
   swap_its(__gnu_debug::_Safe_sequence_base& __lhs,
 	   __gnu_debug::_Safe_iterator_base*& __lhs_its,
@@ -90,6 +94,7 @@ namespace
     swap_its(__lhs, __lhs._M_const_iterators,
 	     __rhs, __rhs._M_const_iterators);
   }
+#pragma GCC diagnostic pop
 
   template<typename _Action>
     void