<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/96941>96941</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            memcpy() missing from clang's intrin.h on Windows
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          a-p-jo
      </td>
    </tr>
</table>

<pre>
    To reproduce this issue:
Try to compile the below code on clang on windows (for example, if installed through visual studio, run `clang <filename>.c` in the Developer Command Prompt):

```c
#include <intrin.h>

int main(void)
{
        memcpy((void *)0xdeadbeef, (void *)(0xdeadbeef+1), 1);
}
```

The following error message will be printed:
```c
error: call to undeclared library function 'memcpy' with type 'void *(void *, const void *, unsigned int)'; ISO C99 and later do not support
      implicit function declarations [-Wimplicit-function-declaration]
      |         memcpy((void *)0xdeadbeef, (void *)(0xdeadbeef+1), 1);
      |         ^
note: include the header <string.h> or explicitly provide a declaration for 'memcpy'
```
Refer [microsoft documentation](https://learn.microsoft.com/en-us/cpp/intrinsics/intrinsics-available-on-all-architectures): `mempcy` is listed under a table titled "_The following UCRT functions have intrinsic forms on all architectures:_".  So, the symbol should be defined in `intrin.h`.

The code compiles with gcc (minGW) as well as msvc (visual studio built tools). 

Upon some ctrl+click-ing to and ctrl+f-ing through the `intrin.h` (and its `#include`s) that `clangd` uses in visual studio code on windows, it appears that the llvm/clang version of this header file does not export the symbol `memcpy`, when it should. 
</pre>
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