<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/120855>120855</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Missed tysan violation with optimization
        </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>
    With `-O0 -fsanitize=type`, we detect the violation correctly, but fail to with `-O1` or greater:
```
#include <stdbool.h>

typedef struct k {
    int a;
    int b;
} k;

typedef struct l {
    bool a;
    bool b;
} l;

k my_k;
l my_l;

void frobnicate_the_struct(k *my_k) {
    int a = ((k*) &my_k)->a;
 __builtin_printf("got k.a=%d\n", a);
}

int main() {
 frobnicate_the_struct((k*)&my_l);
}
```

```
$ clang -O0 -fsanitize=type a.c -o a && ./a
==1==ERROR: TypeSanitizer: type-aliasing-violation on address 0x7ffcfff2a198 (pc 0x5f6739b118d1 bp 0x7ffcfff2a110 sp 0x7ffcfff2a0b8 tid 1)
READ of size 4 at 0x7ffcfff2a198 with type int (in k at offset 0) accesses an existing object of type p1 _ZTS1k
    #0 0x5f6739b118d0 (/app/output.s+0x2a8d0)

got k.a=977714280
```

```
$ clang -O1 -fsanitize=type a.c -o a && ./a
got k.a=1389137000
```

godbolt: https://godbolt.org/z/cYPT3vYnY
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJyUVM1u6zgPfRp6QySQKP8uvHCbevfhfugtMOhsAtmWE00Uy7DktunTD-RkmjRzB5gBElgSycND8kjSOb0blCoheYBkE8nZ7-1U-r1y8hj-UWO7U_mb9nuElK1-MFz1Tg7a608FYuNPo4KUAT3iu8JOedV69HuFb9oa6bUdsLXTpFpvTsGpmT32Uhv0Ft-_QDmkDO2Eu0lJryYQFbAqwJ5_rAISemjN3CkE8eh811hr1nsQT8HIqkCjUz06P82txwNC9gCsQkTUg0cJ4nbbnLeQbfBwWf4NwtxAhGS3GMv-BsR8gRzweNpeME1YX01vVnfYT7YZdCu92vq92p5zAeUHBKqWUCruuSOIDQLlwQ2oWjwovTivQDz9xWy7bWZtvB6246QH3y8xtLMeD2sJYgOUdJA8DkAURiGBiq8azhxDvqPUwxL5ReSfSF8JnfmYe8DbAd7PM8bWyGGHv1QUynWLKxtqpxQoxTVQLUOc2IDY8PPn6fn5xzOICl9Oo_p5QQjiwYCxkkZLp4fd6ipFO6Dsukk5h-wj6_u273uSvMhDf8cW2UfSp5koGs7zjmMzfnPjDN23E9bk6HWHPBTOquenaoO2R6c_FcYo_X2SRfBLfaHRQLke8BD8bN875ZGFpsu2Vc4ph3JA9aGd18MObfNHuFi2P4ePHLe_v_zkh4tOgAT7Tp6dFVPLcQSq7ezH2a8d0AP7IJl37MwYWHWVR5FlGY8pZ_9-dPw_jO6aiIu84CJj7BeZdrZrrPFhiHvvRxeeAqqB6othbacdUP0JVLev_38Rb6_Da9SVoitEISNV8kzEOU_SLI_2JbE26VMpZEKNagUrkrzPUi6YUhRz2Ue6JEYxJ-LEeSzyteBJ0eZx15Foc0pziJk6Sm3WxrwdQ-5IOzerkhPLkyQyslHGLW8n0aDecbGG-5VsoqkMQatm3jmImdHOuyuM196o8n_aOdWhPzk53LyYi07s6PVRfy4n0TyZ8q4f2u_nZt3aI1AdYC-f1TjZoBWgeiHjgOoL27eS_gwAAP__-JG98w">