[Bug fortran/57957] [F03] Double free with allocatable components

["songtao.thu at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57957

--- Comment #3 from Tao Song <songtao.thu at gmail dot com> ---
(In reply to janus from comment #2)
> (In reply to Tobias Burnus from comment #1) 
> > For GCC 4.9, one needs to wrap the code in the main program in BLOCK/END
> > BLOCK as otherwise the end-of-scope deallocation does not trigger, which
> > causes the failure.
> 
> Updated test case:
> 
> 
> program main
> 
>   implicit none
> 
>   type :: type1
>     real, allocatable :: anum(:)
>   end type
> 
>   type :: type2
>     type(type1) :: temp
>   end type
> 
> 
>   block
>     type(type1) :: t1
>     type(type2) :: t2
> 
>     t1 = type1([0.,1.])
>     t2 = type2(t1)
>   end block
> end
> 
> 
> 
> Note: The double free goes away when changing the line
> 
> t2 = type2(t1)
> 
> to
> 
> t2%temp = t1
> 
> That means the actual problem is not the auto-dealloc itself (which is done
> properly), but the construction of t2: With the second variant, a deep copy
> is done (allocating a separate chunk of memory for t2%temp), while in the
> first one t2%temp only gets a reference to the memory allocated for t1
> (which is of course wrong). Since both t1 and t2 are auto-deallocated, we
> try to free that memory twice.

Do you mean in fortran the default structure constructor would yield a shadow
copying? Is this in the standard?

Thank you.

Tao Song