[llvm] [CodeGen] Replace (Min,Max)CSFrameIndex with flag on frame object [NFCI] (PR #170905)

[Benjamin Maxwell via llvm-commits]

================
@@ -762,6 +766,18 @@ class MachineFrameInfo {
     return Objects[ObjectIdx+NumFixedObjects].isStatepointSpillSlot;
   }
 
+  bool isCalleeSavedObjectIndex(int ObjectIdx) const {
+    assert(unsigned(ObjectIdx + NumFixedObjects) < Objects.size() &&
+           "Invalid Object Idx!");
+    return Objects[ObjectIdx + NumFixedObjects].isCalleeSaved;
+  }
+
+  void setIsCalleeSavedObjectIndex(int ObjectIdx, bool IsCalleeSaved) {
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MacDue wrote:

nit: Would it make sense to default this to true? I'm not sure passing `true` at each callsite adds much. 
```suggestion
  void setIsCalleeSavedObjectIndex(int ObjectIdx, bool IsCalleeSaved = true) {
```

https://github.com/llvm/llvm-project/pull/170905