<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/120671>120671</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Missed detection of aliasing violaion with tysan
        </td>
    </tr>

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

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

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

<pre>
    This comes from a (invalid) testcase reported at https://gcc.gnu.org/PR118141.

```c
#include <stdio.h>

typedef unsigned int v8u32 __attribute__((vector_size(32)));
typedef unsigned short v8b16 __attribute__((vector_size(16)));

// Function to convert 8 fp32 values to 8 bfloat16 values
// We assume that subnormal numbers are not passed. i.e. The CPU is set to do FTZ.
void convert_fp32_to_bfloat16(void* input, unsigned short* output) {
    v8u32 input_vec;
    for (int i = 0; i < 8; i++) {
        input_vec[i] = ((unsigned int*) input)[i];
    }

 v8u32 shifted_vec = input_vec >> 16;  
    v8b16 result_vec = __builtin_convertvector(shifted_vec, v8b16);
    
    for (int i = 0; i < 8; i++) {
        output[i] = result_vec[i];
    }
}

int main() {
 float input[8] = {
        1.0f, 2.0f, 3.0f, 4.0f, 
        5.0f, 6.0f, 7.8f, 8.0f
    };
    
    unsigned short output[8];

    // Convert fp32 to bfloat16
    convert_fp32_to_bfloat16(input, output);

    // Print output (bfloat16 values as hex)
    for (int i = 0; i < 8; i++) {
 printf("bfloat16 value %d: 0x%04x\n", i, output[i]);
    }

 return 0;
}
```

```
$ clang -O3 -march=x86-64-v3 -fsanitize=type
bfloat16 value 0: 0x3f80
bfloat16 value 1: 0x4000
bfloat16 value 2: 0x4040
bfloat16 value 3: 0x4080
bfloat16 value 4: 0x40a0
bfloat16 value 5: 0x40c0
bfloat16 value 6: 0x40f9
bfloat16 value 7: 0x4100
```

godbolt link: https://godbolt.org/z/jd41as4EW
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJykVV2PqzYQ_TXOyygIbD4feMjH5q3qqtrqSn1BBkzwLdgRHri799dXNoRks2krtStWDhzP8ZkzY5sbI89KiJxEexIdN3zEVg85tsLw3v5vSl1_5G-tNFDpXhhoBt0DB0JTqSbeyZrQDFAYrLgRMIiLHlDUwBFaxIshbEfoidDTuaq8sxo9PZwJPb3-FgRpEAYe8Xf2if35qewLZVJV3VgLIOxgsJbaawl7mafix0XUooFROeU1SIUwpSOjUBQccZDliKIoCE0JTSdRoR4KI38KQlNGCc2Wh-2fkZlWD5auDOJ_pwviBzon3iYLp1FVKLUC1FBpNYkBIYXmwihMvBuFsUAKZdNpjkG8fLzFfxPAjRl7AdhyBDOWSg8970CNfSkGA3wQoDTChRsjag-kJzx4awUcXn8HacAItEvUGk5vf1iXJy3rq5TCCilQF9f1bWralnIHUl1GJPTw4ImF9IgOy4AkNl0AWJx3QcUkqtkHCzR6mJsEQQJhR_AJ27ufB0jdT0L37rmns383smgvSXR00bP_90UndGdjF73ZMvkmgCTHuSSLRtPKBkVtiR3jugzY3mIvEMRWFqyJ2R4YhBk7XGOKohxlh1IVi5NzQxCa3rFb81z02hdOzv-1ZXH_zpObuL9L_mqBXa7nUjkXV2JX_MXAaJ-uVn9aNvD8xmZEl5EtY7iMd1Oj5VO8jImXujG17zddj5Y8bL41z3TN6Dp_3huHZT-53YR63UTLrH_o8bW3105-xv86WLvmKbZWD5sUuIFWvNvg_1zSi12icdWgn-mB0KgmbAf-O6GRH76T6KAIpVa1vJO-FPxTh60NPwgcB-V03LrgesQ-nLjuzAmh6rg6w_ZXBtueD1VL2PE9jbdxuJ0YbBvDlUR76rGjPTOJv3uQ7c-aWZP6X8FgBkPffwLSKxg-AdkVfEYbXkH-BIyuYPUEjK9gk30FkwUMnNoH3866LnWH0En1p533cMnN6HLJ_ST09L0OA27Cl2-bOmd1xjK-EXmQsDCOKUuCTZuHNMjKTDSc0ZonYRX7Ycb8kgoepCyJk43MqU_DgFLfpyxjgRdnCfPDiPkBryLWxCT0Rc9l53Xd1Nu1N9KYUeQB9eMk2HS8FJ1xNzylSvwAh9qeio6bIbdB23I8GxL6nTRobjQosRP5L9JeMVALFPOdphvgneRGqjNMUnfcfvwhsQX8MFxtxqHLH3yR2I6lV-me0JOlX4btZdDfRYWEnpwoQ-hpUT3l9K8AAAD__wIbgZM">