[Bug fortran/64927] New: [4.7/4.8 Regression] Surprising error with -Wsurprising (-Wall) and TRANSFER + C_ASSOCIATED

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64927

            Bug ID: 64927
           Summary: [4.7/4.8 Regression] Surprising error with
                    -Wsurprising (-Wall) and TRANSFER + C_ASSOCIATED
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anlauf at gmx dot de

The following error occurs with 4.7 and 4.8, but not with 4.6 or 4.9.
The error is slightly annoying since -Wsurprising is automatically
enabled by -Wall, and it was a try-and-error by a colleague to trace
the problem to -Wsurprising.

The error shows up only if both indicated code lines with TRANSFER
and C_ASSOCIATED are active, commenting out any of them makes the
error disappear.  The dump-tree for 4.8 and 4.9 does not show
any difference if -Wno-surprising is set.  The error is bogus.

> cat gfcbug130.f90
! gfortran -c gfcbug130.f90 -Wall
! false error, compare -Wsurprising vs. -Wno-surprising

module surprise
  use iso_c_binding
  implicit none
  TYPE t_pointer
     TYPE(c_ptr) :: cptr
  END TYPE t_pointer
contains
  SUBROUTINE get_pointer (ibuf)
    INTEGER, INTENT(IN) :: ibuf(:)
    TYPE(t_pointer)     :: zp
! Error disappears if any line is commented out:
    zp = TRANSFER (ibuf, zp)
    IF (C_ASSOCIATED (zp% cptr)) Print *, "OK"
  END SUBROUTINE get_pointer
end module surprise

> gfc-48 -c gfcbug130.f90 -Wall       
gfcbug130.f90:16.22:

    IF (C_ASSOCIATED (zp% cptr)) Print *, "OK"
                      1
Error: Type mismatch in argument 'c_ptr_1' at (1); passed INTEGER(4) to
TYPE(c_ptr)

> gfc-48 -c gfcbug130.f90 -Wall -Wno-surprising

The problem does not occur in 4.9.  If there is an
easy fix for 4.8, could it be backported?

(I understand that the 4.7 branch is already closed.)

Thanks,
Harald