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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/99307] FAIL: gfortran.dg/class_assign_4.f90   -O0 
 execution test
Date: Mon, 01 Mar 2021 11:16:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99307

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

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

--- Comment #4 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to Dominique d'Humieres from comment #1)
> Reduced test

While -fsanitize=3Daddress,undefined does not find anything on x86_64-gnu-l=
inux,
I do see with valgrind:

=3D=3D98347=3D=3D Invalid write of size 8
=3D=3D98347=3D=3D    at 0x40397E: test_t1_ (ijd.f90:43)
=3D=3D98347=3D=3D    by 0x403A4E: MAIN__ (ijd.f90:60)
=3D=3D98347=3D=3D    by 0x403A85: main (ijd.f90:61)
=3D=3D98347=3D=3D  Address 0x4f55c98 is 8 bytes inside a block of size 12 a=
lloc'd
=3D=3D98347=3D=3D    at 0x483DFAF: realloc (in
/usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
=3D=3D98347=3D=3D    by 0x402A6D: test_t1_ (ijd.f90:40)
=3D=3D98347=3D=3D    by 0x403A4E: MAIN__ (ijd.f90:60)
=3D=3D98347=3D=3D    by 0x403A85: main (ijd.f90:61)

That's:
  x =3D [t2(1,10.0),t2(2,20.0),t2(3,30.0)]
  y =3D x
  x =3D realloc_t1 (y) ! <<< line 40, 8 bytes alloc'd inside block of size =
12
  x =3D realloc_t1 (x)
  x =3D x(3:1:-1) + y
  x =3D [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 =E2=80=93 at least not if the required size increased in the assign=
ment. (The
valgrind message implies that shrinking did work in line 40.)=