<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/109634>109634</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] Can't compile RISC-V vector intrisics with precompiled headers (PCH)
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          Ferdi265
      </td>
    </tr>
</table>

<pre>
    ## Summary

Clang supports RISC-V vector intrinsics (`#include <riscv_vector.h>`), but fails to compile them when precompiled headers (PCH) are being used. This affects [clangd](https://github.com/clangd/clangd/issues/2143) since it precompiles the header-portion of source files.

## Testcase

Dependencies on Debian/Ubuntu: clang, gcc-multilib

```c
// test.h
#ifndef TEST_H_
#define TEST_H_

#include <riscv_vector.h>

#endif
```

```c
// test.c
#include "test.h"

vuint64m4_t v_add(vuint64m4_t a, vuint64m4_t b, size_t vl) {
    return __riscv_vadd_vv_u64m4(a, b, vl);
}
```

Compile without PCH:

```shell
$ clang --target=riscv64-linux-gnu -march=rv64gcv -c test.c -o test.o
```

Compile with PCH:

```shell
$ clang --target=riscv64-linux-gnu -march=rv64gcv -x c-header test.h -o test.h.pch
$ clang --target=riscv64-linux-gnu -march=rv64gcv -include-pch test.h.pch -c test.c -o test.o
test.c:4:12: error: call to undeclared function '__riscv_vadd_vv_u64m4'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    4 |     return __riscv_vadd_vv_u64m4(a, b, vl);
      |            ^
test.c:4:12: error: returning 'int' from a function with incompatible result type 'vuint64m4_t' (aka '__rvv_uint64m4_t')
    4 |     return __riscv_vadd_vv_u64m4(a, b, vl);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy0Vk2P2zYT_jX0ZSBDS0qWfdDBa6-RnN4X3W17NChyJLGlKIEfSraH_vaCktarbJNtgCCCYQvD-XhmODOPuXOqMYglye9Jft7w4Nvelhe0UtFdvql6-VwSyghl8Bi6jttnkp5Jepy_T5qbBlwYht56B798fDwlv8GIwvcWlPFWGaeEA0L3ZJcSypQROkgEwk5WOTFeZ91tS9jDpHEg9ARV8FBzpR34HkTfDUoj-BY7-NSigcHiIpTQIpdopwj_P30g9ADcIlSoTAPBodzCU6sc8LpG4R2Q_F5EzJLkZ0L3rfeDI-xI6IXQS6N8G6qt6DtCL4va6kU5F9AReqF3GYuRnDICQfkVIBdhLqCSWBTVG-hrcH2wAqGOKtt1BZfaPqHzgjtcH51xQCPRCIUOegNnrBQ3hF5-rYLxgbAjTNhixRohki5or7SqvnC_S-ePeAkXEwWPzm_bGwJVG4k1PD08Pl0_XG9iibUy-EZ8s3nvJr9URSNV_QbP94IU_w5I6QKf0rWXMSjjd1mXXT2MVy4lofu1jMc6rQVVFDj1F0YDHS-UFPezLwAAiz5YA9frkh6X8jqO1xCtCd1P7iYXky1hiykpzu-kelqa-ZPybR88xJ5lx68Ww7Wo9Uv22XzVkCSe2wY9YecJ1i5LtDLhc9KYAEnHrWjj0bjLGjFCIpYiQtLPb_13YvvZwD6DSOYpWXrxhrDdDqL9Qe9LqySDaFdOv12OpdPYMSPseEfjZKG1vZ1GjGsd11AwEoXmFiXUwYhpsAktvtEeBWH38PHxf3A6HIAbCZp7tCB7ML1_WZigukErofyrxzkGj-_Tskp-f9FJXnSSlU7cYreGzYAUJ_iB1p1sb06Wh-QP_12kOWDcuYQWynhCC6ht3wF_TW1qK2XiouReVRrBogvag38e4lQXq9mM9hHon3ypcUS_Po2wf0biJH_4-91nNqBz6g4aNGi5R7l9MyQbWTJ5YAe-wfKuoEW6T_O02LSlxCrfSS441jSTTErJsCp2ktYHzmieblRJU5qlB8rSPcvTYiuqO1nLFNn-sKNc5iRLseNKb7Ueu21vm83ETOVdetixbKN5hdpNhE7pQhA0crsto0FShcaRLNXKeffqwiuvp38Bs0V-hlPkmsLf-Pcr5D5x-3Sv71LyJlhdvkO1EcTykwy2_wOFX9PtktdY0n8CAAD__zm-qQA">