libstdc++: Remove noexcept from match_results comparisons (PR 94627)

These functions can't be noexcept because the iterators stored in the
sub_match objects can throw on any operation.

libstdc++-v3/ChangeLog:

	PR libstdc++/94627
	* include/bits/regex.h (operator==, operator!=): Remove noexcept
	equality comparisons for match_results.
	* testsuite/28_regex/match_results/94627.cc: New test.

(cherry picked from commit a1a0dc4548979f8a340a7ea71624a52a20e1e0b3)

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

@@ -2099,7 +2099,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   template<typename _Bi_iter, typename _Alloc>
     inline bool
     operator==(const match_results<_Bi_iter, _Alloc>& __m1,
-	       const match_results<_Bi_iter, _Alloc>& __m2) noexcept
+	       const match_results<_Bi_iter, _Alloc>& __m2)
     {
       if (__m1.ready() != __m2.ready())
 	return false;
@@ -2124,7 +2124,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   template<typename _Bi_iter, class _Alloc>
     inline bool
     operator!=(const match_results<_Bi_iter, _Alloc>& __m1,
-	       const match_results<_Bi_iter, _Alloc>& __m2) noexcept
+	       const match_results<_Bi_iter, _Alloc>& __m2)
     { return !(__m1 == __m2); }
 #endif
 

libstdc++-v3/testsuite/28_regex/match_results/94627.cc

+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run { target c++11 } }
+
+#include <regex>
+#include <testsuite_hooks.h>
+
+struct iterator
+{
+  using value_type = char;
+  using difference_type = std::ptrdiff_t;
+  using reference = char&;
+  using pointer = char*;
+  using iterator_category = std::bidirectional_iterator_tag;
+
+  iterator() : ptr() { }
+  explicit iterator(pointer p) : ptr(p) { }
+
+  iterator& operator++() { if (bang) throw 1; ++ptr; return *this; }
+  iterator operator++(int) { auto copy = *this; ++*this; return copy; }
+  iterator& operator--() { if (bang) throw 1; --ptr; return *this; }
+  iterator operator--(int) { auto copy = *this; --*this; return copy; }
+
+  reference operator*() const noexcept { return *ptr; }
+  pointer operator->() const noexcept { return ptr; }
+
+  bool operator==(iterator rhs) const noexcept { return ptr == rhs.ptr; }
+  bool operator!=(iterator rhs) const noexcept { return ptr != rhs.ptr; }
+
+  static bool bang;
+
+private:
+  pointer ptr;
+};
+
+bool iterator::bang = false;
+
+int main()
+{
+  char str[] = "abc";
+  std::regex r(str);
+  std::match_results<iterator> m;
+  std::regex_match(iterator(str), iterator(str+3), m, r);
+  iterator::bang = true;
+  bool caught = false;
+  try {
+    (void) (m == m);
+  } catch (int) {
+    caught = true;
+  }
+  VERIFY( caught );
+  caught = false;
+
+  try {
+    (void) (m != m);
+  } catch (int) {
+    caught = true;
+  }
+  VERIFY( caught );
+}