<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/86521>86521</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Using flang for external tools requires specifying host endianness
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            flang
      </td>
    </tr>

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

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

<pre>
    Several headers in flang require `FLANG_BIG_ENDIAN` or `FLANG_LITTLE_ENDIAN` to be defined. This causes compile-time errors when using the headers, for example in an out-of-tree flang-based tool. A minimum reproducer is the file below

```
#include <flang/Frontend/CompilerInvocation.h>
```

Compiling this in the most straightforward way produces this compile-time error.

```
include/flang/Common/uint128.h:269:2: error: #error host endianness is not known
```

This is not ideal. Tools should not be required to specify the host endianness themselves. 

I have a draft PR [here](https://github.com/llvm/llvm-project/pull/86516) which replaces these preprocessor defines with equivalents from LLVM.

</pre>
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