<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64684>64684</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Undefined behavior sanitizer missed case with uninitialized arrays 
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            enhancement,
            compiler-rt:ubsan
      </td>
    </tr>

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

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

<pre>
    I found this based on reading https://discourse.llvm.org/t/clang-assigning-an-uninitialized-array-to-another-array-produces-undefined-behavior-with-optimization-o1/72763 

the following code which I believe is undefined behavior based on 
`the value of an object with automatic storage duration is used while it is indeterminate” (C99 draft).`

is not detected by `-fsanitize=undefined,address`

```
#include <stdio.h>

#define N 4
int ia[N];
int main (void) { 
    int i, ib[N];
  
    for (i = 0; i < N; i++)
        ia[i] = ib[i];

    /* check results: */  
    for (i = 0; i < N; i++)
       printf("%d : %d\n",ia[i], ib[i]);

    return 0;
}

```
The output does change based on optimization levels which indicates to me that this is undefined behavior 

https://godbolt.org/z/s9T6TdEbd
</pre>
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