[llvm] [AssumeBundles] Dereferenceable used in bundle only applies at assume. (PR #126117)

[Philip Reames via llvm-commits]

================
@@ -1474,7 +1474,11 @@ Currently, only the following parameter attributes are defined:
     ``null_pointer_is_valid`` function attribute is present.
     ``n`` should be a positive number. The pointer should be well defined,
     otherwise it is undefined behavior. This means ``dereferenceable(<n>)``
-    implies ``noundef``.
+    implies ``noundef``. When ``dereferenceable(<n>)`` is used in an
+    :ref:`assume operand bundls <assume_opbundles>`, the pointer is only
+    guaranteed to be dereferenceable at the point of the assumption and
+    may not be dereferenceable at later pointers, e.g. because it could have
+    been freed.
----------------
preames wrote:

I agree, but we do need some kind of reference here to catch the readers eye.  Something along the lines of "Use of the dereferenceable keyword on an assume operand bundle is not a argument or return attribute, and has different semantics."

https://github.com/llvm/llvm-project/pull/126117