[llvm] [SDAG][NVPTX] Cache control metadata support and lowering (PR #204067)

[Matt Arsenault via llvm-commits]

================
@@ -129,6 +129,18 @@ struct MachinePointerInfo {
 ///
 class MachineMemOperand {
 public:
+  /// LLVM IR metadata carried by a MachineMemOperand.
+  struct Metadata {
+    AAMDNodes AAInfo;
+    const MDNode *Ranges;
+    const MDNode *MemCacheHint;
+
+    Metadata() : Ranges(nullptr), MemCacheHint(nullptr) {}
----------------
arsenm wrote:

```suggestion
    const MDNode *Ranges = nullptr;
    const MDNode *MemCacheHint = nullptr;

    Metadata() = default;
```

https://github.com/llvm/llvm-project/pull/204067