[clang] [X86] Allow PSHUFD/PSHUFLW/PSHUFW intrinsics in constexpr. (PR #161210)

[Simon Pilgrim via cfe-commits]

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@@ -2773,6 +2773,62 @@ static bool interp__builtin_blend(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+enum class Half { None, Low, High };
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RKSimon wrote:

this seems unnecessary - why not just `bool IsShufHW`?

https://github.com/llvm/llvm-project/pull/161210