<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/155111>155111</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [OpenCL] [Driver] -finclude-default-header causes generating broken preprocessed sources generation on clang crash.
        </td>
    </tr>

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

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

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

<pre>
    Due to driver passing it no matter what, there result will be multiple definitions of of every definition in `opencl-c-base.h`

Since this file contains not only declarations, but also definitions and it is not guarded, crash reproduces are bogus eg.:

```
/home/prak/DEV/build-clang-runtimes/lib/clang/22/include/opencl-c-base.h:390:14: error: redefinition of 'memory_scope'
  390 | typedef enum memory_scope {
 | ^
/home/prak/DEV/build-clang-runtimes/lib/clang/22/include/opencl-c-base.h:390:14: note: previous definition is here
  390 | typedef enum memory_scope {
 |              ^
```

```
In file included from <built-in>:1:
/home/prak/DEV/build-clang-runtimes/lib/clang/22/include/opencl-c-base.h:570:3: error: typedef redefinition with different types ('struct ndrange_t' vs 'struct ndrange_t')
  570 | } ndrange_t;
      | ^
/home/prak/DEV/build-clang-runtimes/lib/clang/22/include/opencl-c-base.h:570:3: note: previous definition is here
  570 | } ndrange_t;
```

and for `__cplusplus` also:

```
In file included from <built-in>:1:
/home/prak/DEV/build-clang-runtimes/lib/clang/22/include/opencl-c-base.h:667:32: error: redefinition of '__remove_address_space'
  667 | template <typename _Tp> struct __remove_address_space { using type = _Tp; };
      | ^
/home/prak/DEV/build-clang-runtimes/lib/clang/22/include/opencl-c-base.h:667:32: note: previous definition is here
  667 | template <typename _Tp> struct __remove_address_space { using type = _Tp; };
```
(Multiple times - since it has definition for each address space)

If this file must exist, it scope should probably be limited to declarations only, or `-finclude-default-header` should be filtered out from cc1 command line in crash reproducers. 
Probably doing both would be good.
Right now `-finclude-default-header` in such case is passed twice in reproducer script in addition to preprocessed sources already containing
 content of `opencl-c-base.h`


</pre>
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