[Bug libstdc++/114817] Wrong codegen for std::copy of "trivially copyable but not trivially assignable" type

[arthur.j.odwyer at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114817

--- Comment #3 from Arthur O'Dwyer  ---
https://github.com/boostorg/container/issues/153 , from 2020, is another
similar issue. There, boost::container::vector had assumed that if
__has_trivial_copy(T) and is_copy_constructible_v, then T could be relocated
via memcpy; but in fact __has_trivial_copy(T) is also true for move-only types.
So it was possible to create a type such that (__has_trivial_copy(T) &&
__is_constructible(T, T&)) and yet not __is_trivially_constructible(T, T&).

// https://godbolt.org/z/x5Wda1M6E
struct T {
template T(U&&);
T(T&&);
~T();
};
static_assert(__has_trivial_copy(T) && __is_constructible(T, T&));
  // ...and yet...
static_assert(not __is_trivially_constructible(T, T&));

[Bug libstdc++/114817] Wrong codegen for std::copy of "trivially copyable but not trivially assignable" type

[de34 at live dot cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114817

Jiang An  changed:

   What|Removed |Added

 CC||de34 at live dot cn

--- Comment #2 from Jiang An  ---
Bug 106547 seems somehow related.

[Bug libstdc++/114817] Wrong codegen for std::copy of "trivially copyable but not trivially assignable" type

[arthur.j.odwyer at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114817

--- Comment #1 from Arthur O'Dwyer  ---
Yes, vector reallocation has analogous trouble with types that are "trivial,
but not trivially copy constructible."
https://godbolt.org/z/Psboqf3MP

(libc++ happens to sidestep this pitfall *on Clang 15+,* because libc++ gates
their vector reallocation optimization differently depending on whether
`__has_builtin(__is_trivially_relocatable)`; but libc++ would have the same bug
as libstdc++ when compiled on GCC.)