[clang] [llvm] [IR] Make dead_on_return attribute optionally sized (PR #171712)

[Antonio Frighetto via llvm-commits]

================
@@ -60,6 +60,40 @@ enum class AllocFnKind : uint64_t {
   LLVM_MARK_AS_BITMASK_ENUM(/* LargestValue = */ Aligned)
 };
 
+class DeadOnReturnInfo {
+public:
+  DeadOnReturnInfo() : DeadBytes(std::nullopt) {}
+  DeadOnReturnInfo(uint64_t DeadOnReturnBytes) : DeadBytes(DeadOnReturnBytes) {}
+
+  uint64_t getNumberOfDeadBytes() {
+    assert(DeadBytes.has_value() &&
+           "This attribute does not specify a byte count. Did you forget to "
+           "check if the attribute covers all reachable memory?");
+    return DeadBytes.value();
+  }
+
+  bool coversAllReachableMemory() { return !DeadBytes.has_value(); }
----------------
antoniofrighetto wrote:

```suggestion
  bool coversAllReachableMemory() const { return !DeadBytes.has_value(); }
```

https://github.com/llvm/llvm-project/pull/171712