[llvm] [IR][PatternMatch] Only accept poison in getSplatValue() (PR #89159)

[Nikita Popov via llvm-commits]

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@@ -448,7 +448,10 @@ define <2 x i1> @icmp_power2_and_icmp_shifted_mask_vector_swapped_splat_poison_2
 ; Vector of 2 reduction with splat containing undef
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nikic wrote:

The reason I didn't change these tests to use poison is that there are already existing test variants with poison, so I just kept both.

https://github.com/llvm/llvm-project/pull/89159