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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/106434] [12/13 Regression] Spurious -Wnull-dereference when
 using std::unique_copy() since r12-5187-g1ae8edf5f73ca5c3
Date: Wed, 30 Nov 2022 14:44:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106434

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Slightly simpler, with correct assertion now:

--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -139,6 +139,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     {
       const size_type __n =3D __position - begin();
       if (this->_M_impl._M_finish !=3D this->_M_impl._M_end_of_storage)
+       {
+         __glibcxx_assert(__position !=3D const_iterator());
+         if (__position =3D=3D const_iterator())
+           __builtin_unreachable(); // PR 106434
+
          if (__position =3D=3D end())
            {
              _GLIBCXX_ASAN_ANNOTATE_GROW(1);
@@ -159,6 +164,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
              _M_insert_aux(__position, __x);
 #endif
            }
+       }
       else
 #if __cplusplus >=3D 201103L
        _M_realloc_insert(begin() + (__position - cbegin()), __x);


The __builtin_unreachable would be unnecessary if __glibcxx_assert expanded=
 to
that when assertions are disabled (so the macro expands to either an assert=
ion,
or a hint that the condition is always true). I think I tried that and it
caused problems though.=