[llvm] Add 'initialized' attribute langref (PR #84803)

[Haopeng Liu via llvm-commits]

================
@@ -1621,6 +1621,31 @@ Currently, only the following parameter attributes are defined:
     ``readonly`` or a ``memory`` attribute that does not contain
     ``argmem: write``.
 
+``initialized((Lo1,Hi1),...)``
+    This attribute indicates that the function initializes the ranges of the
+    pointer parameter's memory, [%p+LoN, %p+HiN): there are no reads, and no
+    special accesses (such as volatile access or untrackable capture) before
+    the initialization write in the function.
+
+    This attribute implies that the function initializes and does not read
----------------
haopliu wrote:

Done!

https://github.com/llvm/llvm-project/pull/84803