<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/55189>55189</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang trunk missed the buffer-overflow in code
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          shao-hua-li
      </td>
    </tr>
</table>

<pre>
    For the following code, both `clang-tk -fsanitize=address -O0` and `-O3` do not report the global-buffer-overflow of `a[]`. Interestingly, if you change `M` to a smaller value (e.g., `#define M 2`), they could detect it. Initially I thought it may relate to optimizations as discussed in https://github.com/llvm/llvm-project/issues/53972. But it's clearly not because changing `#define M 5` affected the result and even `-O0` missed the bug.
```c
#define M 5
volatile int a[M];
__attribute__((__noinline__))
void b(x) {
    if(x) a[M] = 7;
}
main(){ 
    b(M); 
    __builtin_printf("a[M]=%d\n", a[M]);
}
```

</pre>
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