libgfortran/runtime/deep_copy.c

/* Deep copy support for allocatable components in derived types.
   Copyright (C) 2025-2026 Free Software Foundation, Inc.

This file is part of the GNU Fortran runtime library (libgfortran).

Libgfortran is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.

Libgfortran is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.

You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
<http://www.gnu.org/licenses/>.  */

#include "libgfortran.h"
#include <string.h>

/* Runtime helper for deep copying allocatable array components when the
   element type contains nested allocatable components.  The front end handles
   allocation and deallocation; this helper performs element-wise copies using
   the compiler-generated element copier so that recursion takes place at
   runtime.  */

static inline size_t
descriptor_elem_size (gfc_array_void *desc)
{
  size_t size = GFC_DESCRIPTOR_SIZE (desc);
  return size == 0 ? 1 : size;
}

void
cfi_deep_copy_array (gfc_array_void *dest, gfc_array_void *src,
		     void (*copy_element) (void *, void *))
{
  int rank;
  size_t src_elem_size;
  size_t dest_elem_size;
  index_type extent[GFC_MAX_DIMENSIONS];
  index_type src_stride_bytes[GFC_MAX_DIMENSIONS];
  index_type dest_stride_bytes[GFC_MAX_DIMENSIONS];
  index_type count[GFC_MAX_DIMENSIONS];
  char *src_ptr;
  char *dest_ptr;

  if (src == NULL || dest == NULL)
    return;

  if (GFC_DESCRIPTOR_DATA (src) == NULL)
    {
      if (GFC_DESCRIPTOR_DATA (dest) != NULL)
        internal_error (NULL, "cfi_deep_copy_array: destination must be "
                              "deallocated when source is not allocated");
      return;
    }

  if (GFC_DESCRIPTOR_DATA (dest) == NULL)
    internal_error (NULL, "cfi_deep_copy_array: destination not allocated");

  rank = GFC_DESCRIPTOR_RANK (src);
  src_elem_size = descriptor_elem_size (src);
  dest_elem_size = descriptor_elem_size (dest);

  if (rank <= 0)
    {
      memcpy (GFC_DESCRIPTOR_DATA (dest), GFC_DESCRIPTOR_DATA (src),
              src_elem_size);
      if (copy_element != NULL)
        copy_element (GFC_DESCRIPTOR_DATA (dest),
                      GFC_DESCRIPTOR_DATA (src));
      return;
    }

  for (int dim = 0; dim < rank; dim++)
    {
      extent[dim] = GFC_DESCRIPTOR_EXTENT (src, dim);
      if (extent[dim] <= 0)
        return;

      src_stride_bytes[dim]
        = GFC_DESCRIPTOR_STRIDE (src, dim) * src_elem_size;
      dest_stride_bytes[dim]
        = GFC_DESCRIPTOR_STRIDE (dest, dim) * dest_elem_size;
      count[dim] = 0;
    }

  src_ptr = (char *) GFC_DESCRIPTOR_DATA (src);
  dest_ptr = (char *) GFC_DESCRIPTOR_DATA (dest);

  while (true)
    {
      memcpy (dest_ptr, src_ptr, src_elem_size);
      if (copy_element != NULL)
        copy_element (dest_ptr, src_ptr);

      dest_ptr += dest_stride_bytes[0];
      src_ptr += src_stride_bytes[0];
      count[0]++;

      int dim = 0;
      while (count[dim] == extent[dim])
        {
          count[dim] = 0;
          dest_ptr -= dest_stride_bytes[dim] * extent[dim];
          src_ptr -= src_stride_bytes[dim] * extent[dim];
          dim++;
          if (dim == rank)
            return;
          count[dim]++;
          dest_ptr += dest_stride_bytes[dim];
          src_ptr += src_stride_bytes[dim];
        }
    }
}

export_proto(cfi_deep_copy_array);