[Bug tree-optimization/107087] [12/13 Regression] bits/stl_algobase.h:431: warning: 'void* __builtin_memcpy(void*, const void*, unsigned int)' reading between 8 and 2147483644 bytes from a region of size 4 [-Wstringop-overread]

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107087

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This prevents the warning:

--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -911,13 +911,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ///  null-termination.
       size_type
       size() const _GLIBCXX_NOEXCEPT
-      { return _M_rep()->_M_length; }
+      {
+#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0 && __OPTIMIZE__
+       if (_M_rep() == &_S_empty_rep() && _M_rep()->_M_length != 0)
+         __builtin_unreachable();
+#endif
+       return _M_rep()->_M_length;
+      }

       ///  Returns the number of characters in the string, not including any
       ///  null-termination.
       size_type
       length() const _GLIBCXX_NOEXCEPT
-      { return _M_rep()->_M_length; }
+      {
+#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0 && __OPTIMIZE__
+       if (_M_rep() == &_S_empty_rep() && _M_rep()->_M_length != 0)
+         __builtin_unreachable();
+#endif
+       return _M_rep()->_M_length;
+      }

       ///  Returns the size() of the largest possible %string.
       size_type