[Bug c++/110714] New: constexpr lifetime error: base class this pointer

[pkeir at outlook dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110714

            Bug ID: 110714
           Summary: constexpr lifetime error: base class this pointer
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pkeir at outlook dot com
  Target Milestone: ---

Compiling the C++20 MRE code below fails:

struct Base
{
  constexpr virtual ~Base() {}
  constexpr Base* get_this() { return this; }
  int x;
};

struct Derived : public Base {};

constexpr bool test()
{
  Derived* pf = new Derived;
  delete pf->get_this();
  return true;
}

constexpr bool b = test();

...with the following error message:

2$ /opt/gcc-latest/bin/g++ -std=c++20 -c ce_base_alloc2.cpp 
ce_base_alloc2.cpp:17:24:   in ‘constexpr’ expansion of ‘test()’
ce_base_alloc2.cpp:13:23:   in ‘constexpr’ expansion of
‘pf->Derived::<anonymous>.Base::get_this()->Base::~Base()’
ce_base_alloc2.cpp:8:8: error: deallocation of storage that was not previously
allocated
    8 | struct Derived : public Base {};
      |        ^~~~~~~

I have tried with GCC trunk (14.0.0) and also version 12.2.0.

I suspect that the this pointer in the base class is not tracking the constexpr
dynamic allocation. Clang and MSVC both compile successfully. Clang requires
the virtual destructor.