<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/140693>140693</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [X86] Poor emulation of cmpss pattern
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:X86,
            missed-optimization
      </td>
    </tr>

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

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

<pre>
    https://simd.godbolt.org/z/nqP1WxY1q

Inspired by #140563

```c
#include <x86intrin.h>

__m128 test_cmpeqss(__m128 x, __m128 y) {
    int cmp = y[0] == x[0];
    return _mm_setr_ps(__builtin_bit_cast(float, -cmp), x[1], x[2], x[3]);
}
```

We never quite manage to recreate the single (v)cmpeqss

-march=x86-64
```asm
test_cmpeqss: # @test_cmpeqss
# %bb.0: # %entry
  cmpeqss %xmm0, %xmm1
  movss %xmm1, %xmm0 # xmm0 = xmm1[0],xmm0[1,2,3]
  retq
```

-march=x86-64-v3
```asm
test_cmpeqss: # @test_cmpeqss
# %bb.0: # %entry
  vcmpeqss %xmm0, %xmm1, %xmm1
  vmovd %xmm1, %eax
  vmovd %eax, %xmm1
  vblendps $1, %xmm1, %xmm0, %xmm0 # xmm0 = xmm1[0],xmm0[1,2,3]
  retq
```

-march=x86-64-v4
```asm
test_cmpeqss: # @test_cmpeqss
# %bb.0: # %entry
  vcmpeqss %xmm0, %xmm1, %k0
  kmovw %k0, %eax
  negl %eax
  vmovd %eax, %xmm1
  vblendps $1, %xmm1, %xmm0, %xmm0 # xmm0 = xmm1[0],xmm0[1,2,3]
  retq
```
</pre>
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