[llvm] XCOFF associated metadata (PR #159096)

[Wael Yehia via llvm-commits]

================
@@ -8440,6 +8440,35 @@ Example:
 The ``nofree`` metadata indicates the memory pointed by the pointer will not be
 freed after the attached instruction.
 
+'``ref``' Metadata
+^^^^^^^^^^^^^^^^^^
+
+The ``ref`` metadata may be attached to a global variable definition with a
+single argument that references a global object. The metadata is lowered to a
+.ref directive which will emit a relocation introducing an explicit dependence
+to the referenced symbol. This is typically used when there is some implicit
+dependence between the symbols that is otherwise opaque to the linker. One such
+example is metadata which is accessed by a runtime with associated
+``__start_<section_name>`` and ``__stop_<section_name>`` symbols.
+
+This metadata lowers to the .ref assembly directive which will add a relocation
----------------
w2yehia wrote:

We already described what the MD is lowered too.

https://github.com/llvm/llvm-project/pull/159096