[llvm] [PGO] Add llvm.loop.estimated_trip_count metadata (PR #152775)

[Nikita Popov via llvm-commits]

================
@@ -7966,6 +7966,54 @@ The attributes in this metadata are added to all followup loops of the
 loop distribution pass. See
 :ref:`Transformation Metadata <transformation-metadata>` for details.
 
+'``llvm.loop.estimated_trip_count``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This metadata records an estimated trip count for the loop.  The first operand
+is the string ``llvm.loop.estimated_trip_count``.  The second operand is an
+integer constant of type ``i32`` or smaller specifying the estimate.  For
----------------
nikic wrote:

What's the motivation for allowing "or smaller"?

https://github.com/llvm/llvm-project/pull/152775