[Bug fortran/77504] [8/9/10/11 Regression] "is used uninitialized" with allocatable string and array constructors

[dev-zero at gentoo dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77504

Tiziano Müller <dev-zero at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dev-zero at gentoo dot org

--- Comment #19 from Tiziano Müller <dev-zero at gentoo dot org> ---
I have yet another (more complicated) case, but this time not reproducible with
gcc-7.5, only with 9 and 10:

** snip: 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
*** end snip ***

*** snip: modb.f90 ***
module modb
    use moda, only: funca
contains
   PURE SUBROUTINE funcb(oarr)
      REAL, DIMENSION(:), INTENT(OUT)    :: oarr
      REAL, ALLOCATABLE, DIMENSION(:, :) :: arr

      oarr(:) = 0.0

      CALL funca(arr, ubound(oarr, 1))
      oarr = MATMUL(TRANSPOSE(arr), oarr)*1.
   END SUBROUTINE funcb
end module
*** end snip ***

building with:

gfortran -O1 -Werror=uninitialized -c moda.f90
gfortran -O1 -Werror=uninitialized -c modb.f90

triggers:

*** snip: output ***
modb.f90:11:0:

   11 |       oarr = MATMUL(TRANSPOSE(arr), oarr)*1.
      | 
Error: ‘__var_1_matmul.dim[0].lbound’ is used uninitialized in this function
[-Werror=uninitialized]
modb.f90:11:0: Error: ‘__var_1_matmul.dim[0].ubound’ is used uninitialized in
this function [-Werror=uninitialized]
f951: some warnings being treated as errors
*** end snip ***

Removing either the `*1` at the end or the call to `transpose` makes the
warning/error go away. As does using `-O0`.