[Bug fortran/99307] FAIL: gfortran.dg/class_assign_4.f90 -O0 execution test

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99307

--- Comment #5 from Paul Thomas <pault at gcc dot gnu.org> ---
(In reply to Tobias Burnus from comment #4)
> (In reply to Dominique d'Humieres from comment #1)
> > Reduced test
> 
> While -fsanitize=address,undefined does not find anything on
> x86_64-gnu-linux, I do see with valgrind:
> 
> ==98347== Invalid write of size 8
> ==98347==    at 0x40397E: test_t1_ (ijd.f90:43)
> ==98347==    by 0x403A4E: MAIN__ (ijd.f90:60)
> ==98347==    by 0x403A85: main (ijd.f90:61)
> ==98347==  Address 0x4f55c98 is 8 bytes inside a block of size 12 alloc'd
> ==98347==    at 0x483DFAF: realloc (in
> /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==98347==    by 0x402A6D: test_t1_ (ijd.f90:40)
> ==98347==    by 0x403A4E: MAIN__ (ijd.f90:60)
> ==98347==    by 0x403A85: main (ijd.f90:61)
> 
> That's:
>   x = [t2(1,10.0),t2(2,20.0),t2(3,30.0)]
>   y = x
>   x = realloc_t1 (y) ! <<< line 40, 8 bytes alloc'd inside block of size 12
>   x = realloc_t1 (x)
>   x = x(3:1:-1) + y
>   x = [t2(1,10.0),t2(2,20.0),t2(3,30.0)] ! <<< line 43, invalid write of
> size 8
> 
> Looking at the Fortran code,
>   x and y have the dynamic type T2 until 'realloc_t1', which turns this into
> the dynamic type T1.
> 
> In the last line (line 43), the dynamic type changes again to T2.
> 
> In terms of memory usage: 3*8bytes before the first realloc_t1 call, then
> 3*4bytes and for the last line again 3*8bytes.
> 
>  * * *
> 
> It seems as if the reallocation does not work properly if the dynamic type
> changes – at least not if the required size increased in the assignment.
> (The valgrind message implies that shrinking did work in line 40.)

I am unable to see why this is happening. The valgrind complaints go away if a
different array size is assigned before the changes in type. For some reason,
it seems that the vptr->size is not being read correctly or is never set.

Paul