[Bug fortran/96312] Reallocation on assignment uses undefined variables

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96312

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=77504
                 CC|                            |dev-zero at gentoo dot org

--- Comment #1 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Slightly sanitized test case from the originating PR, by Tiziano Müller:

$ cat moda.f90
module moda
contains
   PURE SUBROUTINE funca(arr, sz)
      REAL, ALLOCATABLE, DIMENSION(:, :), INTENT(OUT) :: arr
      integer, intent(in) :: sz
      allocate(arr(sz, sz))
      arr(:, :) = 0.
   END SUBROUTINE
end module
$ cat modb.f90
module modc
    use moda, only: funca
contains
   PURE SUBROUTINE funcb(oarr)
      REAL, DIMENSION(:), INTENT(OUT)    :: oarr
      REAL, ALLOCATABLE, DIMENSION(:, :) :: arr
      real, allocatable, dimension(:) :: tmp
      CALL funca(arr, ubound(oarr, 1))
      tmp = matmul(transpose(arr),oarr)
      oarr = tmp*1.
   END SUBROUTINE funcb
end module

Compiled with -O1 -Wall, this yields
$ gfortran -Wall -O1 -c moda.f90 modb.f90
modb.f90:8:0:

    8 |       oarr = MATMUL(TRANSPOSE(arr), oarr)*1.
      | 
Warning: '__var_1_matmul.dim[0].lbound' is used uninitialized in this function
[-Wuninitialized]
modb.f90:8:0: Warning: '__var_1_matmul.dim[0].ubound' is used uninitialized in
this function [-Wuninitialized]


Front-end optimization introduces an extra assignment statement here,
this version also shows the warning:

$ cat modc.f90
module modc
    use moda, only: funca
contains
   PURE SUBROUTINE funcb(oarr)
      REAL, DIMENSION(:), INTENT(OUT)    :: oarr
      REAL, ALLOCATABLE, DIMENSION(:, :) :: arr
      real, allocatable, dimension(:) :: tmp
      CALL funca(arr, ubound(oarr, 1))
      tmp = matmul(transpose(arr), oarr)
      oarr = tmp*1.
   END SUBROUTINE funcb
end module

The warning seems to be correct:

$ grep __var_1_matmul modb.f90.004t.original 
        struct array01_real(kind=4) __var_1_matmul;
            __var_1_matmul.data = 0B;
              __var_1_matmul.dtype = {.elem_len=4, .rank=1, .type=3};
              D.3969 = __var_1_matmul;
              D.3970 = (real(kind=4)[0:] * restrict) __var_1_matmul.data == 0B;
              __builtin_free ((void *) __var_1_matmul.data);
              __var_1_matmul.data = D.3969.data;
              D.3971 = ((__var_1_matmul.dim[0].lbound - D.3969.dim[0].lbound) -
__var_1_matmul.dim[0].ubound) + D.3969.dim[0].ubound != 0;
              D.3973 = D.3972 ? 1 : __var_1_matmul.dim[0].lbound;
              __var_1_matmul.dim[0].lbound = D.3973;
              __var_1_matmul.dim[0].ubound = D.3969.dim[0].ubound + D.3973;
              __var_1_matmul.dim[0].stride = 1;
              __var_1_matmul.offset = D.3974;
              D.4003 = (real(kind=4)[0:] * restrict) __var_1_matmul.data;
              D.4004 = __var_1_matmul.offset;
              D.4005 = __var_1_matmul.dim[0].lbound;
              D.4006 = __var_1_matmul.dim[0].ubound;
            if ((real(kind=4)[0:] * restrict) __var_1_matmul.data != 0B)
                __builtin_free ((void *) __var_1_matmul.data);
                (real(kind=4)[0:] * restrict) __var_1_matmul.data = 0B;

So, something seems to be wrong with reallocation on assignment here.