<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - 'Incomplete type' error when mapping a global extern std::array"
   href="https://bugs.llvm.org/show_bug.cgi?id=50508">50508</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>'Incomplete type' error when mapping a global extern std::array
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>OpenMP
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Runtime Library
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>jtramm@anl.gov
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>An error occurs when compiling the following file (transfer.cpp) that attempts
to map a global scope std::array object declared as extern:

#include<array>
#pragma omp declare target
extern std::array<double, 4> arr;
#pragma omp end declare target
void copy_host_to_device()
{
  #pragma omp target update to(arr)
}
void copy_device_to_host()
{
  #pragma omp target update from(arr)
}

Compiled with clang++ (version 13.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
59d938e649e62db0cef4903d495e838fbc6a6eb8) for a V100 target as:

clang++ -Wall -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -Xopenmp-target
-march=sm_70 -c transfer.cpp -o transfer.o

The error given is:

transfer.cpp:9:32: error: incomplete type 'std::array<double, 4>' where a
complete type is required
  #pragma omp target update to(arr)
                               ^~~
transfer.cpp:9:3: error: expected at least one 'to' clause or 'from' clause
specified to '#pragma omp target update'
  #pragma omp target update to(arr)
  ^
transfer.cpp:14:34: error: incomplete type 'std::array<double, 4>' where a
complete type is required
  #pragma omp target update from(arr)
                                 ^~~
transfer.cpp:14:3: error: expected at least one 'to' clause or 'from' clause
specified to '#pragma omp target update'
  #pragma omp target update from(arr)
  ^
4 errors generated.

As a workaround (found by Johannes Doerfert), it works if the array is
instantiated in the first function as:

void copy_host_to_device()
{
  arr[0];
  #pragma omp target update to(arr)
}

The code for this reproducer is available at:

<a href="https://github.com/jtramm/omp_target_issues/blob/master/array_simple/transfer.cpp">https://github.com/jtramm/omp_target_issues/blob/master/array_simple/transfer.cpp</a>

and a larger version with a main can be found at:

<a href="https://github.com/jtramm/omp_target_issues/tree/master/array">https://github.com/jtramm/omp_target_issues/tree/master/array</a></pre>
        </div>
      </p>


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