[llvm-branch-commits] [llvm] [AMDGPUUsage] Specify what one-as syncscopes do (PR #189016)

[Fabian Ritter via llvm-branch-commits]

================
@@ -1153,102 +1153,114 @@ This is different to the OpenCL [OpenCL]_ memory model which does not have scope
 inclusion and requires the memory scopes to exactly match. However, this
 is conservatively correct for OpenCL.
 
-  .. table:: AMDHSA LLVM Sync Scopes
-     :name: amdgpu-amdhsa-llvm-sync-scopes-table
-
-     ======================= ===================================================
-     LLVM Sync Scope         Description
-     ======================= ===================================================
-     *none*                  The default: ``system``.
-
-                             Synchronizes with, and participates in modification
-                             and seq_cst total orderings with, other operations
-                             (except image operations) for all address spaces
-                             (except private, or generic that accesses private)
-                             provided the other operation's sync scope is:
-
-                             - ``system``.
-                             - ``agent`` and executed by a thread on the same
-                               agent.
-                             - ``workgroup`` and executed by a thread in the
-                               same work-group.
-                             - ``wavefront`` and executed by a thread in the
-                               same wavefront.
-
-     ``agent``               Synchronizes with, and participates in modification
-                             and seq_cst total orderings with, other operations
-                             (except image operations) for all address spaces
-                             (except private, or generic that accesses private)
-                             provided the other operation's sync scope is:
-
-                             - ``system`` or ``agent`` and executed by a thread
-                               on the same agent.
-                             - ``workgroup`` and executed by a thread in the
-                               same work-group.
-                             - ``wavefront`` and executed by a thread in the
-                               same wavefront.
-
-     ``cluster``             Synchronizes with, and participates in modification
-                             and seq_cst total orderings with, other operations
-                             (except image operations) for all address spaces
-                             (except private, or generic that accesses private)
-                             provided the other operation's sync scope is:
-
-                             - ``system``, ``agent`` or ``cluster`` and
-                               executed by a thread on the same cluster.
-                             - ``workgroup`` and executed by a thread in the
-                               same work-group.
-                             - ``wavefront`` and executed by a thread in the
-                               same wavefront.
-
-                             On targets that do not support workgroup cluster
-                             launch mode, this behaves like ``agent`` scope instead.
-
-     ``workgroup``           Synchronizes with, and participates in modification
-                             and seq_cst total orderings with, other operations
-                             (except image operations) for all address spaces
-                             (except private, or generic that accesses private)
-                             provided the other operation's sync scope is:
-
-                             - ``system``, ``agent`` or ``workgroup`` and
-                               executed by a thread in the same work-group.
-                             - ``wavefront`` and executed by a thread in the
-                               same wavefront.
-
-     ``wavefront``           Synchronizes with, and participates in modification
-                             and seq_cst total orderings with, other operations
-                             (except image operations) for all address spaces
-                             (except private, or generic that accesses private)
-                             provided the other operation's sync scope is:
-
-                             - ``system``, ``agent``, ``workgroup`` or
-                               ``wavefront`` and executed by a thread in the
-                               same wavefront.
-
-     ``singlethread``        Only synchronizes with and participates in
-                             modification and seq_cst total orderings with,
-                             other operations (except image operations) running
-                             in the same thread for all address spaces (for
-                             example, in signal handlers).
-
-     ``one-as``              Same as ``system`` but only synchronizes with other
-                             operations within the same address space.
-
-     ``agent-one-as``        Same as ``agent`` but only synchronizes with other
-                             operations within the same address space.
-
-     ``cluster-one-as``      Same as ``cluster`` but only synchronizes with other
-                             operations within the same address space.
-
-     ``workgroup-one-as``    Same as ``workgroup`` but only synchronizes with
-                             other operations within the same address space.
-
-     ``wavefront-one-as``    Same as ``wavefront`` but only synchronizes with
-                             other operations within the same address space.
-
-     ``singlethread-one-as`` Same as ``singlethread`` but only synchronizes with
-                             other operations within the same address space.
-     ======================= ===================================================
+There is a ``one-as`` variant for each sync scope. If a ``release`` or
+``acquire`` operation with a ``one-as`` sync scope participates in a
+synchronization, only the effects of memory operations in the address space of
+the ``one-as`` operation are synchronized. The address space of a ``fence``
+instruction with ``one-as`` sync scope is specified via
+``amdgpu-synchronize-as`` MMRAs (see :ref:`amdgpu-fence-as`).
----------------
ritter-x2a wrote:

It would be nice to get rid of one-as, and MMRAs were intended to and might be the way to do that. I think resolving this is on our TODO list.
But currently, one-as is still there (in this document, in tests, in the backend, and in the IR we generate for OpenCL), and therefore it makes sense to me to document what it's supposed to do.

https://github.com/llvm/llvm-project/pull/189016