[llvm] [CodeGen] Add complete-schedule search strategy API (PR #220644)

[Matt Arsenault via llvm-commits]

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@@ -305,6 +306,31 @@ class LLVM_ABI MachineSchedStrategy {
   virtual void releaseBottomNode(SUnit *SU) = 0;
 };
 
+/// Interface for transforming one complete legal schedule into another.
+///
+/// The incoming complete schedule is denoted as Founder. It can be either
+/// the initial serialized nodenum schedule before scheduler runs or the
+/// completed schedule after scheduler ran.
+struct LLVM_ABI MachineSchedCompleteScheduleOptimizer {
+public:
+  virtual ~MachineSchedCompleteScheduleOptimizer();
+
+  /// Optimize Founder and write a complete region-local SUnit permutation to
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arsenm wrote:

I'm not sure what "Founder" is. It's just an array of integers, optimize them how?

https://github.com/llvm/llvm-project/pull/220644