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

[Antonio Frighetto via cfe-commits]

================
@@ -1855,7 +1859,9 @@ Currently, only the following parameter attributes are defined:
 
     This attribute does not imply aliasing properties. For pointer arguments that
     do not alias other memory locations, ``noalias`` attribute may be used in
-    conjunction. Conversely, this attribute always implies ``dead_on_unwind``.
+    conjunction. Conversely, this attribute always implies ``dead_on_unwind``. If
+    a number of bytes is specified, then only those bytes are implied to be
+    ``dead_on_unwind``.
----------------
antoniofrighetto wrote:

```suggestion
    conjunction. Conversely, this attribute always implies ``dead_on_unwind``. When
    a byte count is specified, ``dead_on_unwind`` is implied only for that range.
```

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