[llvm] [AMDGPU] Allocate AVRegClass last (PR #146606)

[Matt Arsenault via llvm-commits]

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@@ -109,6 +109,10 @@ class SIRegisterClass <string n, list<ValueType> rTypes, int Align, dag rList>
   let TSFlags{2} = HasVGPR;
   let TSFlags{3} = HasAGPR;
   let TSFlags{4} = HasSGPR;
+
+  // RegisterClass (e.g. AGPR / VGPR) priority for allocation
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arsenm wrote:

I think this needs more commentary on how this interacts with the real priority. Maybe call this BasePriority or something? 

https://github.com/llvm/llvm-project/pull/146606