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

[Alex Bradbury via llvm-commits]

================
@@ -15230,6 +15230,62 @@ 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_memset_pattern:
+
+'``llvm.memset_pattern``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This is an overloaded intrinsic. You can use ``llvm.memset_pattern`` on
+any integer bit width that is an integral number of bytes and for different
+address spaces. Not all targets support all bit widths however.
+
+::
+
+      declare void @llvm.memset_pattern.p0.i64.i128(ptr <dest>, i128 <val>,
+                                                    i64 <len>, i1 <isvolatile>)
+
+Overview:
+"""""""""
+
+The '``llvm.memset_pattern.*``' intrinsics fill a block of memory with
----------------
asb wrote:

The intrinsic is indeed named `llvm.memset_pattern`, so these do match the implementation in the current PR:

```
def int_memset_pattern
    : Intrinsic<[],
      [llvm_anyptr_ty, llvm_anyint_ty, llvm_anyint_ty, llvm_i1_ty],
      [IntrWriteMem, IntrArgMemOnly, IntrWillReturn, IntrNoFree, IntrNoCallback,
       NoCapture<ArgIndex<0>>, WriteOnly<ArgIndex<0>>,
       ImmArg<ArgIndex<3>>], "llvm.memset_pattern">;
```

Did you want to advocate for instead calling it `llvm.memset.pattern`?

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