[llvm] [InstSimplify] Remove most of undef handling logic (PR #119884)

[Nikita Popov via llvm-commits]

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@@ -826,81 +826,43 @@ define <2 x i8> @rotr_zero_shift_guard_splat(<2 x i8> %x, <2 x i8> %sh) {
   ret <2 x i8> %s
 }
 
-; If first two operands of funnel shift are undef, the result is undef
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nikic wrote:

I think it makes sense to keep the undef test coverage (just showing that no fold happens, which still ensures that no incorrect fold happens).

https://github.com/llvm/llvm-project/pull/119884