Clang rejects valid program involving evaluation of this in constexpr context

[ranaanoop]

The following valid program is rejected by clang: Demo

struct X
{
  const void *p_;

  consteval X()
    : p_{this}
  {
  }
};

static constexpr X x{};

The bug was first reported here: https://stackoverflow.com/questions/78381492/is-the-address-of-a-consteval-constructed-object-a-constant-expression

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Anoop Rana (ranaanoop)

The following valid program is rejected by clang: [Demo](https://godbolt.org/z/YaKM81aT4)

struct X
{
  const void *p_;

  consteval X()
    : p_{this}
  {
  }
};

static constexpr X x{};

The bug was first reported here: https://stackoverflow.com/questions/78381492/is-the-address-of-a-consteval-constructed-object-a-constant-expression

[shafik]

Changing the function to constexpr makes clang accept it but EDG rejects both: https://godbolt.org/z/Yfsf514hd

I think this should be well-formed.

CC @cor3ntin

[efriedma-quic]

Is this the same as #89565?

[MitalAshok]

static X x{}; (static constinit X x{};) should also be well-formed. This does correctly compile with #89565

[efriedma-quic]

This is working in C++23 mode... but the original demo was for C++20 mode. Not sure if the C++20 behavior is expected; #89565 says it is, but gcc and MSVC seem to disagree.