PR libstdc++/83600 fix end iterator for unready std::match_results

	PR libstdc++/83600
	* include/bits/regex.h (match_results::end()): Return valid iterator
	when not ready.
	* testsuite/28_regex/match_results/ctors/char/default.cc: Check that
	unready objects are empty and have equal begin and end iterators.
	* testsuite/28_regex/match_results/ctors/wchar_t/default.cc: Likewise.

From-SVN: r256014

libstdc++-v3/ChangeLog

 2017-12-27  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/83600
+	* include/bits/regex.h (match_results::end()): Return valid iterator
+	when not ready.
+	* testsuite/28_regex/match_results/ctors/char/default.cc: Check that
+	unready objects are empty and have equal begin and end iterators.
+	* testsuite/28_regex/match_results/ctors/wchar_t/default.cc: Likewise.
+
 	PR libstdc++/83598
 	* include/bits/regex.h (basic_regex): Don't modify flags passed to
 	constructors.

libstdc++-v3/include/bits/regex.h

@@ -1749,7 +1749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        */
       const_iterator
       end() const
-      { return _Base_type::end() - 3; }
+      { return _Base_type::end() - (empty() ? 0 : 3); }
 
       /**
        * @brief Gets an iterator to one-past-the-end of the collection.

libstdc++-v3/testsuite/28_regex/match_results/ctors/char/default.cc

@@ -30,6 +30,8 @@ void test01()
   std::cmatch cm;
   VERIFY( cm.size() == 0 );
   VERIFY( !cm.ready() );
+  VERIFY( cm.empty() );
+  VERIFY( cm.begin() == cm.end() ); // PR libstdc++/83600
 }
 
 void test02()
@@ -37,6 +39,8 @@ void test02()
   std::smatch sm;
   VERIFY( sm.size() == 0 );
   VERIFY( !sm.ready() );
+  VERIFY( sm.empty() );
+  VERIFY( sm.begin() == sm.end() ); // PR libstdc++/83600
 }
 
 int

libstdc++-v3/testsuite/28_regex/match_results/ctors/wchar_t/default.cc

@@ -30,6 +30,8 @@ void test01()
   std::wcmatch cm;
   VERIFY( cm.size() == 0 );
   VERIFY( !cm.ready() );
+  VERIFY( cm.empty() );
+  VERIFY( cm.begin() == cm.end() ); // PR libstdc++/83600
 }
 
 void test02()
@@ -37,6 +39,8 @@ void test02()
   std::wsmatch sm;
   VERIFY( sm.size() == 0 );
   VERIFY( !sm.ready() );
+  VERIFY( sm.empty() );
+  VERIFY( sm.begin() == sm.end() ); // PR libstdc++/83600
 }
 
 int