================
@@ -16,31 +16,81 @@ internally by the compiler. A thread that initiates one or
more async operations
An *asyncmark* created by a thread can be used to track async operations
initiated by that thread.
+### Stages
+
+A *stage* names a kind of async operation. Each async operation *belongs to*
the
+one stage determined by the instruction that initiates it.
+
+The stages are:
+
+| Bit | Stage | Async operations |
+|---|---|---|
+| 0 | `TENSOR` | tensor loads and stores |
+| 1 | `GLOBAL_LOAD_ASYNC_TO_LDS` | global loads async to LDS |
+| 2 | `GLOBAL_LOAD_ASYNC_TO_LDS_MCAST` | multicast (cluster) global loads
async to LDS |
+| 3 | `GLOBAL_STORE_ASYNC_FROM_LDS` | async global stores from LDS |
+| 5 | `BUFFER_GLOBAL_LOAD` | buffer loads to LDS and pre-gfx1250 global loads
to LDS |
+
+Bits 4 and 6 through 10 are reserved for future async operations, and no
+operation belongs to them yet.
+
+Which async operations a given subtarget actually has is described in
+{ref}`AMDGPU DMA Operations <amdgpu-dma-operations>`. A stage exists on every
+subtarget that supports asyncmarks, whether or not that subtarget has any
+operation belonging to it.
+
+### Stage Masks
+
+Both intrinsics take a *stage mask*: an 11-bit value in which a set bit names a
+stage.
+
+The mask `0` which names no stage is given the special meaning "every stage".
+This ensures if new stages are added that programs will continue to wait on all
+stages, if that was their intention.
+
+Bits not specified in the table above are reserved for future use. It is not an
+error to set them, but it could mean you have more conservative waits than
+necessary when the future stages are added.
+
+Setting a bit that is neither listed nor reserved is an error.
+
+Users are strongly advised to keep bitmasks disjoint in
asyncmark/wait_asyncmark
+operations, or else the resulting program may become rather confusing for them.
+
### Current Sequence
-The abstract machine maintains a sequence of asyncmarks during the execution of
-a function body, which excludes any asyncmarks produced by calls to other
-functions encountered in the currently executing function. The state of this
-sequence at each program point in the function is called the *current
sequence*.
+The abstract machine maintains a separate sequence of asyncmarks *for each
+stage* during the execution of a function body, which excludes any asyncmarks
+produced by calls to other functions encountered in the currently executing
+function. The state of the sequence for a stage `S` at each program point in
+the function is called the *current sequence of* `S`.
-### `@llvm.amdgcn.asyncmark()`
+The sequences of distinct stages are independent: appending to one does not
+affect the length or contents of any other, even though multiple sequences may
+be appended to with a single call to asyncmark (by naming multiple stages).
-Produces an asyncmark and appends it to the current sequence.
+### `@llvm.amdgcn.asyncmark(i32 %K)`
-### `@llvm.amdgcn.wait.asyncmark(i16 %N)`
+Produces an asyncmark in every stage named by the mask `K`, and appends it to
+the current sequence of each. The sequences of the stages `K` does not name are
+unaffected. `K` must be a constant stage mask.
-Ensures that the length of the current sequence is at most `N` by removing
-asyncmarks from the start of the sequence if it is more than `N`.
+### `@llvm.amdgcn.wait.asyncmark(i16 %N, i32 %K)`
+
+For every stage named by the mask `K`, ensures that the length of the current
+sequence of that stage is at most `N` by removing asyncmarks from the start of
+that sequence if it is longer than `N`. The sequences of the stages `K` does
not
+name are unaffected. `K` must be a constant stage mask.
----------------
ssahasra wrote:
```suggestion
name are unaffected. `K` must be a constant stage mask.
[Informationaly note --- Typically, when removing an asyncmark, this intrinsic
*waits* for the async operations corresponding to that asyncmark to complete.]
```
https://github.com/llvm/llvm-project/pull/220442
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