[llvm] [MachinePipeliner] Add an abstract layer to manipulate Data Dependenc… (PR #109918)

[Pengcheng Wang via llvm-commits]

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@@ -59,6 +61,8 @@ namespace llvm {
 class AAResults;
 class NodeSet;
 class SMSchedule;
+class SwingSchedulerDDGEdge;
+class SwingSchedulerDDG;
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wangpc-pp wrote:

Why do we need forward declarations here?

https://github.com/llvm/llvm-project/pull/109918