<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/74623>74623</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc] -Wshift-count-overflow in libc/src/__support/UInt.h
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            code-quality,
            libc
      </td>
    </tr>

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

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

<pre>
    ```
[692/693] Building CXX object projects/libc/src/stdio/prin...s/libc.src.stdio.printf_core.converter.dir/converter.cpp.o
In file included from /android0/llvm-project/libc/src/__support/UInt128.h:12,
                 from /android0/llvm-project/libc/src/__support/FPUtil/FloatProperties.h:12,
                 from /android0/llvm-project/libc/src/__support/FPUtil/FPBits.h:17,
                 from /android0/llvm-project/libc/src/stdio/printf_core/core_structs.h:13,
                 from /android0/llvm-project/libc/src/stdio/printf_core/converter.h:12,
                 from /android0/llvm-project/libc/src/stdio/printf_core/converter.cpp:9:
/android0/llvm-project/libc/src/__support/UInt.h: In instantiation of ‘constexpr __llvm_libc_18_0_0_git::cpp::BigInt<Bits, Signed>::operator T() const [with T = unsigned int; <template-parameter-2-2> = void; long unsigned int Bits = 320; bool Signed = false]’:
/android0/llvm-project/libc/src/__support/float_to_string.h:381:57:   required from here
/android0/llvm-project/libc/src/__support/UInt.h:125:53: warning: left shift count >= width of type [-Wshift-count-overflow]
  125 |       return static_cast<T>((static_cast<T>(val[1]) << 64) + lo);
      |                             ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
```
I'm trying to get -Werror re-enabled in https://github.com/llvm/llvm-project/pull/74506; building with GCC flags the above warning.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy8VU2P2zYQ_TXjy8CCRFpfBx_8sS58W6AbJDeBkiiZLU0q5MjbvfS3F6RtbJJuEbTZRjCsDw7nDd975Ajv1WikXEO-hXy_EDOdrFsb1f3eSy9mbZR0ftHa_mUNRXr7pXtIN5Bvi5oBOxQ1h3yP21npXpkRd58-oW1_kx3h5Gy4e2AHrdoO2MG7-E-9ssAOk1MmSZL7eOJdl8SxJIzQ0HTWyaSz5iIdSZf0ygE7vL5305TYazlHg4PSEpXp9NzLHgdnzwjsIEzvrOrTgKEv5-Wtpm9Laho_T5N1YeDD0VDGquQEfJMxYLsrBH57_QDE4fEDKR0etBX06OwkHSnpfw7m41bRDap8N6gvRb1JF8VysvHk5u6OyP93xLs93pnL78F10wR8UwPf3HbIfzZfrByPBpXxJAwpQcoatAPCA4MqhbrqrPEk_5gcNk1I3YSETVY1aZM2o6JQBd9cSwK-2arxaAj4LigPbIe_hn3fA3-4jgf_CbIOn4BVwGqM-RHy7bOiEz4h8D3OJp4WPaqQaovAdyTPkxYkl5Nw4ixJuiVbMuAPccLFqj4EamvGr2ZjKCOGcJaGiNZafaspfh6E9hLy_X29P8rqELZZQzZYUZkxEsyrDPgmLwPXiE5-npW7Hxwn6eS7qJixPIDwAPIsnFFmDI9aDoT-pAbCzs6GMCqxx2fV0ykITS-TDPQvP8aoZYxa2ot0g7bPgZmbpzOWI5S7m6WdpNkZ9CRIdU0nfND8KSQPslZvfr8IDfk2CzlZHUQFvsNiFV9YEA9YDXz75SZ6BXz7-vMfLsgfrvcrtV93lCOw8ozkXkIXIYujJFx-lM5Zh04upRGtjvbBE9HkgyPYAdhhVHSa26Sz55tAf9dpmnU4-MpVnhbRbvdmFd39y26HgxajRzpJFK29yLtWyaJf877mtVjIdVamWVWlOU8Xp3Xf8rKXeVWs6iLLc5ENUnRiWJW1FGVatwu1ZinjGUuLrOA5TxMmuCzTuspEnXPWC1il8iyUTkKxiXXjQnk_y3W5KhhfaNFK7WNjZqyzvVx-noVW9AIsHmmMXc3HQt9267jgdh49rFKtPPnXrKRIxw4fJ-R7fNtTgdjv-HkxO73-1-THVflIf8H4XwEAAP__kMCh8g">