[Bug fortran/123255] New: OpenACC: copyin of allocatable array component computes wrong size

[albert at tugraz dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123255

            Bug ID: 123255
           Summary: OpenACC: copyin of allocatable array component
                    computes wrong size
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: albert at tugraz dot at
  Target Milestone: ---

current trunk; repo base upstream/master at
769041822723208bf85a91ac409b9b0bdae3fff0 (2025-12-22)

    COLLECT_GCC=/opt/gcc16/bin/gfortran
   
COLLECT_LTO_WRAPPER=/opt/gcc16/libexec/gcc/x86_64-pc-linux-gnu/16.0.0/lto-wrapper
    OFFLOAD_TARGET_NAMES=nvptx-none
    Target: x86_64-pc-linux-gnu
    Thread model: posix
    gcc version 16.0.0 20251222 (experimental) (GCC)

When mapping an allocatable array component of a derived type to the device
using !$acc enter data copyin(obj%array), libgomp computes the wrong size for
the copy operation. It uses the array descriptor size (64 bytes) instead of the
actual allocated data size, causing "invalid size" error.

Reproducer:

  program mre
      use, intrinsic :: iso_fortran_env, only: dp => real64
      implicit none

      type :: container_t
          integer :: n
          real(dp), allocatable :: data(:)
      end type container_t

      type(container_t) :: c
      integer :: i

      c%n = 1000
      allocate(c%data(c%n))
      c%data = [(real(i, dp), i = 1, c%n)]

      print *, "Array size (bytes):", size(c%data) * 8

      !$acc enter data copyin(c%data)

      print *, "PASS"

      !$acc exit data delete(c%data)
  end program mre

Build and run:
    gfortran -O2 -fopenacc -foffload=nvptx-none mre.f90 -o mre
    ACC_DEVICE_TYPE=nvidia ./mre

  Output:
    Array size (bytes):        8000

    libgomp: invalid size

    libgomp: Copying of host object [0x4040c8..0x404108) to dev object
[0x7fd8ab600000..0x7fd8ab600040) failed

  The host object range 0x4040c8..0x404108 is only 64 bytes (0x40), which is
the
  array descriptor size, not the actual data (8000 bytes for 1000 doubles).