[Bug fortran/110415] (Re)allocation on assignment to allocatable polymorphic variable from allocatable polymorphic function result

["burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110415

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |burnus at gcc dot gnu.org

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Andrew Jenner's submitted patch (gcc-patches@ only):
  https://gcc.gnu.org/pipermail/gcc-patches/2023-November/636671.html
and (fortran@ only):
  https://gcc.gnu.org/pipermail/fortran/2023-November/059928.html
(Replies should got to both lists ...)

* * *

Technical it is a regression caused by
 https://gcc.gnu.org/r13-6747-gd7caf313525a46f200d7f5db1ba893f853774aee
but before that commit there was no finalization.

Comparing the versions:
  GCC 7+8: ICE in build_function_decl
  GCC 10+11+12: memory leak in 'func'
  GCC 13+mainline: segfault at runtime  (at 'a = func()' in the main program).

* * *

I had analyzed the issue the elsewhere, let's copy it here for completeness and
possibly to aid the patch review. (Note: The following was written before the
patch was written and analyzed the current status.)

---<cut-----

The 'func' has the prototype 'struct __class_MAIN___P_a func ()', i.e. returns
the class-wrapper directly - and that part looks okay.

However, the assignment somehow mixes everything up:

    D.4349 = a->_vptr;  // save old value of vptr
    D.4328 = func ();   // new value

    desc.0.data = (void * restrict) D.4328._data;
// As scalar, there is not really a problem, but an
//    desc.0.dtype.elem_len = D.4328->_vptr->size;
// is missing here.
    desc.0.span = (integer(kind=8)) desc.0.dtype.elem_len;

    if (__builtin_expect ((integer(kind=8)) (a->_data == 0B), 0, 42))
        a->_data = (struct p *) __builtin_malloc (MAX_EXPR <(unsigned long)
a->_vptr->_size, 1>);
  // WRONG: That should use D.4328->_vptr->size!

    else
      {
        if (a->_vptr != D.4349)
          {
            __builtin_realloc ((void *) a->_data, a->_vptr->_size);

Likewise: a->_vptr should be D.4328->_vptr.

Alternatively, a->_vptr had to be updated before the 'if' block.