[llvm] [PatternMatch] Do not accept undef elements in m_AllOnes() and friends (PR #88217)

[Yingwei Zheng via llvm-commits]

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@@ -965,14 +965,29 @@ define <2 x i1> @substitute_constant_or_ne_slt_swap_vec(<2 x i8> %x, <2 x i8> %y
   ret <2 x i1> %r
 }
 
+; The poison case would be valid to fold.
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dtcxzyw wrote:

```suggestion
; TODO: The poison case would be valid to fold.
```

https://github.com/llvm/llvm-project/pull/88217