[llvm] [IR][NFC] Add LoadStoreProperties to copy load/store attrs (PR #206470)

[Antonio Frighetto via llvm-commits]

================
@@ -172,6 +172,14 @@ class AllocaInst : public UnaryInstruction {
   }
 };
 
+/// A structure representing the attributes of a load or store instruction.
+struct LoadStoreInstAttributes {
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antoniofrighetto wrote:

As we seem to reserve the section header to first-class instructions only, I would not add a dedicated section, and just move it right after the existing Load class banner:
```cpp
//===----------------------------------------------------------------------===//
//                                LoadInst Class
//===----------------------------------------------------------------------===//

/// A structure representing the properties of a load or store instruction.
struct LoadStoreInstProperties {
  bool IsVolatile = false;
  Align Alignment;
  AtomicOrdering Ordering = AtomicOrdering::NotAtomic;
  SyncScope::ID SSID = SyncScope::System;
};

/// An instruction for reading from memory. This uses the SubclassData field in
/// Value to store whether or not the load is volatile.
class LoadInst : public UnaryInstruction {
// ...
```

https://github.com/llvm/llvm-project/pull/206470