[llvm] [Uniformity] Implement per-output machine uniformity analysis (PR #179275)

[Matt Arsenault via llvm-commits]

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@@ -46,6 +47,25 @@ bool llvm::GenericUniformityAnalysisImpl<MachineSSAContext>::markDefsDivergent(
   return InsertedDivergent;
 }
 
+template <>
+bool llvm::GenericUniformityAnalysisImpl<MachineSSAContext>::isAlwaysUniform(
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arsenm wrote:

It should be a Register or MachineInstr+index. IMO we would be better off if all of GIsel was in terms of a MachineValue (Inst+index) similar to SDValue 

https://github.com/llvm/llvm-project/pull/179275