[committed] libstdc++: Support N3644 "Null Forward Iterators" for testsuite iterators

[Jonathan Wakely <jwakely@redhat.com>]

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Comparing value-initialized forward_iterator_wrapper<T> objects fails an
assertion, but should be valid in C++14 and later.

	* testsuite/util/testsuite_iterators.h (forward_iterator_wrapper): Add
	equality comparisons that support value-initialized iterators.

Tested powerpc64le-linux, committed to master.



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commit e94f2542305ccb5c4a3c4e5e8212713747623417
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Feb 27 13:01:14 2020 +0000

    libstdc++: Support N3644 "Null Forward Iterators" for testsuite iterators
    
    Comparing value-initialized forward_iterator_wrapper<T> objects fails an
    assertion, but should be valid in C++14 and later.
    
            * testsuite/util/testsuite_iterators.h (forward_iterator_wrapper): Add
            equality comparisons that support value-initialized iterators.

diff --git a/libstdc++-v3/testsuite/util/testsuite_iterators.h b/libstdc++-v3/testsuite/util/testsuite_iterators.h
index 7b7093919b7..417dff23c50 100644
--- a/libstdc++-v3/testsuite/util/testsuite_iterators.h
+++ b/libstdc++-v3/testsuite/util/testsuite_iterators.h
@@ -337,6 +337,26 @@ namespace __gnu_test
       ++*this;
       return tmp;
     }
+
+#if __cplusplus >= 201402L
+    bool
+    operator==(const forward_iterator_wrapper& it) const noexcept
+    {
+      // Since C++14 value-initialized forward iterators are comparable.
+      if (this->SharedInfo == nullptr || it.SharedInfo == nullptr)
+	return this->SharedInfo == it.SharedInfo && this->ptr == it.ptr;
+
+      const input_iterator_wrapper<T>& base_this = *this;
+      const input_iterator_wrapper<T>& base_that = it;
+      return base_this == base_that;
+    }
+
+    bool
+    operator!=(const forward_iterator_wrapper& it) const noexcept
+    {
+      return !(*this == it);
+    }
+#endif
   };
 
   /**