!fixup improve wording

Author: antoniofrighetto

llvm/docs/LangRef.rst

@@ -1743,15 +1743,18 @@ Currently, only the following parameter attributes are defined:
 
 ``dead_on_return``
     This attribute indicates that the memory pointed to by the argument is dead
-    upon normal function return.
-
-    It is similar to ``byval`` in the regard that it is generally used to pass
-    structs and arrays by value, and the memory is caller-invisible when the
-    function returns. However, unlike ``byval``, it is intended for ABIs where the
-    *callee* explicitly allocates the temporary copy. Stores that would only be
-    visible on the normal return path may be optimized out. Likewise,
-    optimizations may assume that the pointer does not alias any memory that
-    outlives the call.
+    upon normal function return, meaning that the caller will not depend on its
+    contents. Stores that would only be observable on the normal return path may
+    be elided.
+
+    Specifically, the behavior is as-if any memory written through the pointer
+    during the execution of the function is overwritten with a poison value
+    upon normal function return. The caller may access the memory, but any load
+    not preceded by a store will return poison.
+
+    This attribute does not imply aliasing properties. For pointer arguments that
+    do not alias other memory locations, ``noalias`` attribute may be used in
+    conjunction.
 
     This attribute cannot be applied to return values.