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List:       llvm-bugs
Subject:    [llvm-bugs] [Bug 74001] memset doesn't initialize the padding bytes of float3
From:       LLVM Bugs via llvm-bugs <llvm-bugs () lists ! llvm ! org>
Date:       2023-11-30 22:46:28
Message-ID: 20231130224628.02953ab1d0adec29 () email ! llvm ! org
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<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/74001>74001</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            memset doesn&apos;t initialize the padding bytes of float3
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang:codegen
      </td>
    </tr>

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

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

<pre>
    $ cat test.c
```
#include &lt;string.h&gt;

typedef __attribute__((__ext_vector_type__(3))) float float3;

float3 make_float3(float x, float y, float z) {
  float3 r;
  memset(&amp;r, 0, sizeof(float3));
  r.x = x;
  r.y = y;
  r.z = z;
  return r;
}
```
The size of float3 is 16-bytes and the padding bytes should be set to zero, but they \
aren&apos;t.

$ clang -S -o -  test.c -Os -emit-llvm
```
define &lt;3 x float&gt; @make_float3(float noundef %0, float noundef %1, float \
noundef %2) local_unnamed_addr #0 {  %4 = insertelement &lt;3 x float&gt; undef, \
float %0, i64 0  %5 = insertelement &lt;3 x float&gt; %4, float %1, i64 1
  %6 = insertelement &lt;3 x float&gt; %5, float %2, i64 2
 ret &lt;3 x float&gt; %6
}
```

This makes it impossible to compare buffers of float3 objects byte-wise.
</pre>
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