[llvm] [ScheduleDAG] Allow disabling the SchedModel / Itineraries during Scheduling (PR #138057)

[Matt Arsenault via llvm-commits]

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@@ -45,6 +45,9 @@ class TargetSchedModel {
 
   unsigned computeInstrLatency(const MCSchedClassDesc &SCDesc) const;
 
+  bool EnableSchedModel = true;
+  bool EnableSchedItins = true;
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arsenm wrote:

Document these, maybe should just make it an enum for which type to use 

https://github.com/llvm/llvm-project/pull/138057