[llvm] [AMDGPU][StructurizeCFG] Maintain branch MD_prof metadata (PR #109813)

[Matt Arsenault via llvm-commits]

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@@ -85,7 +86,43 @@ using PhiMap = MapVector<PHINode *, BBValueVector>;
 using BB2BBVecMap = MapVector<BasicBlock *, BBVector>;
 
 using BBPhiMap = DenseMap<BasicBlock *, PhiMap>;
-using BBPredicates = DenseMap<BasicBlock *, Value *>;
+
+using MaybeCondBranchWeights = std::optional<class CondBranchWeights>;
+
+class CondBranchWeights {
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arsenm wrote:

Kind of weird this would be defined here, maybe later should just move it to ProfDataUtils (which could use some modernization) 

https://github.com/llvm/llvm-project/pull/109813