[llvm] [AMDGPU][TTI] Add target hook for the custom instruction uniformity (PR #137639)

[Matt Arsenault via llvm-commits]

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@@ -23,7 +23,10 @@ enum class InstructionUniformity {
   AlwaysUniform,
 
   /// The result values can never be assumed to be uniform.
-  NeverUniform
+  NeverUniform,
+
+  /// Result value can be uniform if either of first two operand are uniform.
+  EitherOfFirstTwoOp
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arsenm wrote:

This should be more specifically uses (preferably, any use operand) 

https://github.com/llvm/llvm-project/pull/137639