[llvm] [IR] Initial introduction of memset_pattern (PR #97583)

[Nikita Popov via llvm-commits]

================
@@ -15434,6 +15434,63 @@ The behavior of '``llvm.memset.inline.*``' is equivalent to the behavior of
 '``llvm.memset.*``', but the generated code is guaranteed not to call any
 external functions.
 
+.. _int_experimental_memset_pattern:
+
+'``llvm.experimental.memset.pattern``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use
+``llvm.experimental.memset.pattern`` on any integer bit width and for
+different address spaces. Not all targets support all bit widths however.
+
+::
+
+      declare void @llvm.experimental.memset.pattern.p0.i128.i64(ptr <dest>, i128 <val>,
+                                                                 i64 <count>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.experimental.memset.pattern.*``' intrinsics fill a block of memory
+with a particular value. This may be expanded to an inline loop, a sequence of
+stores, or a libcall depending on what is available for the target and the
+expected performance and code size impact.
+
+Arguments:
+""""""""""
+
+The first argument is a pointer to the destination to fill, the second
+is the value with which to fill it, the third argument is an integer
+argument specifying the number of times to fill the value, and the fourth is a
+boolean indicating a volatile access.
+
+The :ref:`align <attr_align>` parameter attribute can be provided
+for the first argument.
+
+If the ``isvolatile`` parameter is ``true``, the
+``llvm.experimental.memset.pattern`` call is a :ref:`volatile operation
+<volatile>`. The detailed access behavior is not very cleanly specified and it
+is unwise to depend on it.
+
+Semantics:
+""""""""""
+
+The '``llvm.experimental.memset.pattern*``' intrinsic fills memory starting at
+the destination location with the given pattern ``<count>`` times,
+incrementing by the allocation size of the type each time. The stores follows
----------------
nikic wrote:

```suggestion
incrementing by the allocation size of the type each time. The stores follow
```

https://github.com/llvm/llvm-project/pull/97583