<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/162717>162717</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Failure to match signed sub overflow test idiom 
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          sh1boot
      </td>
    </tr>
</table>

<pre>
    Checking for signed integer overflow after an addItion seems to work fine, but this subtraction test gives bad code on multiple architectures (every one I tried, both 32-bit and 64-bit):

```c++
bool idiomatic_check_sub(int x, int y) {
    int64_t result = int64_t(x) - int64_t(y);
    return !(INT_MIN <= result && result <= INT_MAX);
}

bool expected_check_sub(int x, int y) {
    int result;
 return __builtin_ssub_overflow(x, y, &result);
}
```
https://godbolt.org/z/a91sjPzGz

I haven't checked but this issue may generalise across overflow tests for multiple destination data types.  And presumably there's another pattern which people would use when there's no larger temporary type, but I have tested any of those yet.
</pre>
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