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From: "anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/98433] double free detected in tcache 2, after merge of
 structures
Date: Thu, 24 Dec 2020 12:01:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98433

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
                 CC|                            |anlauf at gcc dot gnu.org
   Last reconfirmed|                            |2020-12-24
     Ever confirmed|0                           |1

--- Comment #5 from anlauf at gcc dot gnu.org ---
The user code is alright, it is the implementation of the intrinsic MERGE w=
hich
prevents doing the right thing when assigning to the l.h.s.

Extending the subroutine of the test program to

module bug_merge_m
  implicit none
contains
  subroutine bug_merge
    type t
       real, allocatable :: v(:)
    end type t

    type(t) :: x1, x2, x3, x4, x5
    logical :: f =3D .false.

    allocate(x1%v(1))
    x1%v =3D 1.
    allocate(x2%v(1))
    x2%v =3D 2.
    x3 =3D merge(x1, x2, .false.)
    print *, "x3%v =3D ", x3%v
    x4 =3D merge(x1, x2, f)
    print *, "x4%v =3D ", x4%v
    if (f) then; x5 =3D x1; else; x5 =3D x2; endif
    print *, "x5%v =3D ", x5%v
  end subroutine bug_merge
end module bug_merge_m

and looking a the generated dump-tree, one sees that the assignments to x3 =
and
x4 are generating wrong code, only the assignment to x5 is fine.

@Steve: that's pretty basic F2003 stuff, almost TR15581...=