<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/96690>96690</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [InstCombine] Optimize multiple compares using `xor`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            llvm:instcombine,
            missed-optimization
      </td>
    </tr>

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

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

<pre>
    [This comment](https://github.com/rust-lang/rust/blob/c290e9de32e8ba6a673ef125fde40eadd395d170/library/core/src/char/convert.rs#L232) in the Rust stdlib explains how `(x >= 0x110000) | (x >= 0xD800 && x < 0xE000)` can be computed as `((x ^ 0xD800) - 0x800) >= (0x110000 - 0x800)`, which saves an instruction in LLVM-IR and tends to produce shorter assembly as well. It would be nice if LLVM could do this transformation automatically. I'm not sure how to generalize it to other constants though. 

[godbolt](https://godbolt.org/z/z9GaK7MbY)
[alive](https://alive2.llvm.org/ce/z/brMDvK)
```c
#include <stdbool.h>
#include <stdint.h>

typedef uint32_t u32;

bool src(u32 x) { return (x >= 0x110000) | (x >= 0xD800 && x < 0xE000); }
bool tgt(u32 x) { return ((x ^ 0xD800) - 0x800) >= (0x110000 - 0x800); }
```
</pre>
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