<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/108722>108722</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Invalid rotate-right codegen on x86_64 (LLVM 18)
        </td>
    </tr>

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

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

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

<pre>
    The following test program fails on Clang 18.1.0/x86_64 with -O1 and above:
```c
#include <assert.h>
#include <stdint.h>

uint32_t ror(uint32_t val, uint32_t amount) {
    return (val >> amount) | (val << (32 - amount));
}

__attribute__((noinline))
uint32_t bytesEqual(uint32_t val) {
    return ror(val, 8) == val;
}

int main() {
    assert(!bytesEqual(0x12345612));
}
```
See [on the Compiler Explorer here](https://godbolt.org/z/6aG3eh85M).

Clang 17 produces the following correct output:
```asm
bytesEqual(unsigned int):
        mov     ecx, edi
        rol     ecx, 24
        xor eax, eax
        cmp     ecx, edi
        sete    al
 ret
```

Clang 18 replaces the computation with a `movzx` copying out the lower bytes, and a `shr` to just take the upper byte, i.e. comparing just those two:
```asm
bytesEqual(unsigned int):
        movzx ecx, dil
        shr     edi, 24
        xor     eax, eax
 cmp     ecx, edi
        sete    al
        ret
```

(Reported by "user1234" on the LDC mailing list.)
</pre>
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