[llvm] [Intrinsics][AArch64] Add intrinsic to mask off aliasing vector lanes (PR #117007)

[Sander de Smalen via llvm-commits]

================
@@ -23624,6 +23624,92 @@ Examples:
       %active.lane.mask = call <4 x i1> @llvm.get.active.lane.mask.v4i1.i64(i64 %elem0, i64 429)
       %wide.masked.load = call <4 x i32> @llvm.masked.load.v4i32.p0v4i32(<4 x i32>* %3, i32 4, <4 x i1> %active.lane.mask, <4 x i32> poison)
 
+.. _int_experimental_get_noalias_lane_mask:
+
+'``llvm.experimental.get.noalias.lane.mask.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic.
+
+::
+
+      declare <4 x i1> @llvm.experimental.get.noalias.lane.mask.v4i1(ptr %ptrA, ptr %ptrB, i64 immarg %elementSize, i1 immarg %writeAfterRead)
+      declare <8 x i1> @llvm.experimental.get.noalias.lane.mask.v8i1(ptr %ptrA, ptr %ptrB, i64 immarg %elementSize, i1 immarg %writeAfterRead)
+      declare <16 x i1> @llvm.experimental.get.noalias.lane.mask.v16i1(ptr %ptrA, ptr %ptrB, i64 immarg %elementSize, i1 immarg %writeAfterRead)
+      declare <vscale x 16 x i1> @llvm.experimental.get.noalias.lane.mask.nxv16i1(ptr %ptrA, ptr %ptrB, i64 immarg %elementSize, i1 immarg %writeAfterRead)
+
+
+Overview:
+"""""""""
+
+Create a mask enabling lanes that do not overlap between two pointers
+across one vector loop iteration.
+
+
+Arguments:
+""""""""""
+
+The first two arguments have the same scalar integer type.
+The final two are immediates and the result is a vector with the i1 element type.
+
+Semantics:
+""""""""""
+
+``%elementSize`` is the size of the accessed elements in bytes.
+The intrinsic will return poison if ``%ptrA`` and ``%ptrB`` are within
+VF * ``%elementSize`` of each other and ``%ptrA`` + VF * ``%elementSize`` wraps.
+In other cases when ``%writeAfterRead`` is true, the
+'``llvm.experimental.get.noalias.lane.mask.*``' intrinsics are semantically
+equivalent to:
+
+::
+
+      %diff = (%ptrB - %ptrA) / %elementSize
+      %m[i] = (icmp ult i, %diff) || (%diff <= 0)
+
+When the return value is not poison and ``%writeAfterRead`` is false, the
+'``llvm.experimental.get.noalias.lane.mask.*``' intrinsics are semantically
+equivalent to:
+
+::
+
+      %diff = abs(%ptrB - %ptrA) / %elementSize
+      %m[i] = (icmp ult i, %diff) || (%diff == 0)
----------------
sdesmalen-arm wrote:

```|| %diff == 0```
^^ Ironically this says that if the accesses **fully alias**, the **noalias** intrinsic returns all true.

https://github.com/llvm/llvm-project/pull/117007