[Bug fortran/57906] New: Coarray components: Assignment optimized away (gfortran.dg/coarray/lib_realloc_1.f90)

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57906

            Bug ID: 57906
           Summary: Coarray components: Assignment optimized away
                    (gfortran.dg/coarray/lib_realloc_1.f90)
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org

gfortran.dg/coarray/lib_realloc_1.f90 (r200955) fails if compiled with
optimization. It has:

  type t
    integer, allocatable :: CAF[:]
  end type t
...
  x = y

which gives with -O0 the dump:

    D.1903 = x;
    x = y;
    x.caf = D.1903.caf;

Namely: The fields of the struct "x" are updated from "y" - but the "caf" field
is re-set to the previous value of x.

(Reason: The x.caf.data is a pointer, whose previous address has to be kept.
That's a special feature of coarray components.)


With optimization, the "x.caf = D.1903.caf" line is effectively lost - such
that x.caf.data and y.caf.data point to the same memory.