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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/107852] [12/13 Regression] Spurious warnings
 stringop-overflow and array-bounds copying data as bytes into vector
Date: Tue, 29 Nov 2022 16:50:18 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 12.2.0
X-Bugzilla-Keywords: diagnostic, missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107852

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
With that compiler patch for the missed-optimization one of the two bogus
warnings goes away. The second one goes away with this change:

--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -374,8 +374,19 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       pointer
       _M_allocate(size_t __n)
       {
-       typedef __gnu_cxx::__alloc_traits<_Tp_alloc_type> _Tr;
-       return __n !=3D 0 ? _Tr::allocate(_M_impl, __n) : pointer();
+        pointer __p =3D pointer();
+        if (__n !=3D 0)
+          {
+            typedef __gnu_cxx::__alloc_traits<_Tp_alloc_type> _Tr;
+            const pointer __s =3D _M_impl._M_start;
+            const pointer __f =3D _M_impl._M_finish;
+            const pointer __e =3D _M_impl._M_end_of_storage;
+            __p =3D _Tr::allocate(_M_impl, __n);
+            if (__s !=3D _M_impl._M_start || __f !=3D _M_impl._M_finish
+               || __e !=3D _M_impl._M_end_of_storage)
+              __builtin_unreachable();
+          }
+        return __p;
       }

       _GLIBCXX20_CONSTEXPR=