<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/130452>130452</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang][OpenMP] The include file <omp.h> doesn't compile in C89 mode (it uses the "inline" keyword)
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          quake33
      </td>
    </tr>
</table>

<pre>
    Hello,

Clang 14.0.6 fails to compile the following program (`main.c`):

```c
#include <omp.h>

int main(void) {
  return 0;
}
```

The command producing the error is:

`clang -std=c89 -fopenmp main.c`

The error message is:

```
In file included from main.c:1:
/usr/lib/llvm-14/lib/clang/14.0.6/include/omp.h:493:12: error: unknown type name 'inline'
    static inline int omp_is_initial_device(void) { return 1; }
           ^
1 error generated.
```

I obtained Clang from the official Debian (stable) package.

I think this issue is still relevant today because the keyword `inline` is still written [in the include file <omp.h>](https://github.com/llvm/llvm-project/blob/1649ca5af07a40948ea409ca055330bec1419e72/openmp/runtime/src/include/omp.h.var#L504).


The problem is that `inline` is not a known keyword in C89. Therefore I propose to change [this](https://github.com/llvm/llvm-project/blob/1649ca5af07a40948ea409ca055330bec1419e72/openmp/runtime/src/include/omp.h.var#L502):

```c
# if defined(_OPENMP) && _OPENMP >= 201811
    #pragma omp begin declare variant match(device={kind(host)})
    static inline int omp_is_initial_device(void) { return 1; }
    #pragma omp end declare variant
    #pragma omp begin declare variant match(device={kind(nohost)})
 static inline int omp_is_initial_device(void) { return 0; }
    #pragma omp end declare variant
#   endif
```

into this :


```c
#   if defined(_OPENMP) && _OPENMP >= 201811
#       if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
    #pragma omp begin declare variant match(device={kind(host)})
    static inline int omp_is_initial_device(void) { return 1; }
    #pragma omp end declare variant
    #pragma omp begin declare variant match(device={kind(nohost)})
    static inline int omp_is_initial_device(void) { return 0; }
    #pragma omp end declare variant
#       else
    #pragma omp begin declare variant match(device={kind(host)})
    static int omp_is_initial_device(void) { return 1; }
    #pragma omp end declare variant
    #pragma omp begin declare variant match(device={kind(nohost)})
    static int omp_is_initial_device(void) { return 0; }
    #pragma omp end declare variant
#       endif
#   endif
```

</pre>
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