[llvm] [llvm] Support multiple save/restore points in mir (PR #119357)

[Matt Arsenault via llvm-commits]

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@@ -631,6 +631,61 @@ LLVM_YAML_IS_SEQUENCE_VECTOR(llvm::yaml::CalledGlobal)
 namespace llvm {
 namespace yaml {
 
+// Struct representing one save/restore point in the
+// 'savePoint' / 'restorePoint' list. One point consist of machine basic block
+// name and list of saved/restored in this basic block registers. Generally
+// 'registers' is not obligatory field, if this field is not specified, it is
+// assumed to be equal to the list of all CalleeSavedRegisters, calculated
+// during PEI
+struct SaveRestorePointEntry {
+  StringValue Point;
+  std::vector<StringValue> Registers;
+
+  bool operator==(const SaveRestorePointEntry &Other) const {
+    return Point == Other.Point && Registers == Other.Registers;
+  }
+};
+
+using SaveRestorePoints =
+    std::variant<std::vector<SaveRestorePointEntry>, StringValue>;
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arsenm wrote:

We should make no effort to maintain MIR backwards compatibility. As a diff reduction strategy, this can be part 1. But we should absolutely rip out the old form 

https://github.com/llvm/llvm-project/pull/119357