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From: "tkoenig at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/96312] [10/11 Regression] Reallocation on assignment
 uses undefined variables
Date: Sat, 25 Jul 2020 09:18:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96312

--- Comment #5 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
(In reply to Thomas Koenig from comment #4)

> so it is likely that this patch just started issuing a warning
> for a pre-existing bug in the front end.

That is indeed the case.  Grepping for tmp in the modc.f90 dump yields

  struct array01_real(kind=3D4) tmp;
      tmp.data =3D 0B;
        tmp.dtype =3D {.elem_len=3D4, .rank=3D1, .type=3D3};
        D.2309 =3D tmp;
        D.2310 =3D (real(kind=3D4)[0:] * restrict) tmp.data =3D=3D 0B;
        __builtin_free ((void *) tmp.data);
        tmp.data =3D D.2309.data;
        D.2311 =3D ((tmp.dim[0].lbound - D.2309.dim[0].lbound) -
tmp.dim[0].ubound) + D.2309.dim[0].ubound !=3D 0;
        D.2313 =3D D.2312 ? 1 : tmp.dim[0].lbound;
        tmp.dim[0].lbound =3D D.2313;
        tmp.dim[0].ubound =3D D.2309.dim[0].ubound + D.2313;
        tmp.dim[0].stride =3D 1;
        tmp.offset =3D D.2314;
        D.2343 =3D (real(kind=3D4)[0:] * restrict) tmp.data;
        D.2344 =3D tmp.offset;
        D.2345 =3D tmp.dim[0].lbound;
        D.2346 =3D tmp.dim[0].ubound;
      if ((real(kind=3D4)[0:] * restrict) tmp.data !=3D 0B)
          __builtin_free ((void *) tmp.data);
          (real(kind=3D4)[0:] * restrict) tmp.data =3D 0B;

so there is no way that tmp.dim[0].lbound would have gotten
a value - previous version just didn't see it.=