[llvm] [AMDGPU]: Fall back to default mutations when iglp is not applied (PR #93418)

[Matt Arsenault via llvm-commits]

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@@ -2337,6 +2337,8 @@ class IGroupLPDAGMutation : public ScheduleDAGMutation {
 
   ScheduleDAGMI *DAG;
 
+  std::vector<std::unique_ptr<ScheduleDAGMutation>> *SavedMutations;
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arsenm wrote:

It's not obvious to me why this is a pointer to a vector. Can this just be an ArrayRef? Why does the mutation have to manage the other mutations? I thought all the mutations were added sequentially already, where this would just be one in the set 

https://github.com/llvm/llvm-project/pull/93418