<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/119849>119849</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [x86][CF]Unable to obtain the correct CF flag bit
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          zhaojiangkun-1
      </td>
    </tr>
</table>

<pre>
    Retrieve the CF register flag bit through __readeflags() and verify if the parameters are equal.
Clang generates the 'and' instruction after compilation, and clears the CF flag after executing the 'and' instruction. Is this a bug or is it for some purpose? Resulting in the inability to obtain correct results through __readeflags().

https://godbolt.org/z/4oaWeKxY1


**How did I do it**
1）`clang -g test.c -o -test`
2）`cgdb test`
3)  run to  ` flags = readeflags_test (100, 101)` and debug in assembly
**the debug result**








**test script:**
```#include <x86intrin.h>

extern void abort (void);

#ifdef __x86_64__
#define EFLAGS_TYPE unsigned long long int
#else
#define EFLAGS_TYPE unsigned int
#endif


EFLAGS_TYPE
readeflags_test (unsigned int a, unsigned int b)
{
    volatile char x = (a == b);
    return __readeflags ();
}

int
main ()
{
    EFLAGS_TYPE flags;

    flags = readeflags_test (100, 100);

    if ((flags & 1) != 0)  /* Read CF */
        abort ();

    flags = readeflags_test (100, 101);
    flags = readeflags_test(101, 100);//新增测试用例，用于验证比较对CF的影响


    if ((flags & 1) == 0)  /* Read CF */
        abort ();

#ifdef DEBUG
    printf ("PASSED\n");
#endif

    return 0;
}



</pre>
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