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

[Sander de Smalen via llvm-commits]

================
@@ -23624,6 +23624,90 @@ 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_alias_lane_mask:
+
+'``llvm.experimental.get.alias.lane.mask.*``' Intrinsics
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic.
+
+::
+
+      declare <4 x i1> @llvm.experimental.get.alias.lane.mask.v4i1.i64.i64(i64 %ptrA, i64 %ptrB, i64 immarg %elementSize, i1 immarg %writeAfterRead)
+      declare <8 x i1> @llvm.experimental.get.alias.lane.mask.v8i1.i64.i64(i64 %ptrA, i64 %ptrB, i64 immarg %elementSize, i1 immarg %writeAfterRead)
+      declare <16 x i1> @llvm.experimental.get.alias.lane.mask.v16i1.i64.i32(i64 %ptrA, i64 %ptrB, i32 immarg %elementSize, i1 immarg %writeAfterRead)
+      declare <vscale x 16 x i1> @llvm.experimental.get.alias.lane.mask.nxv16i1.i64.i32(i64 %ptrA, i64 %ptrB, i32 immarg %elementSize, i1 immarg %writeAfterRead)
+
+
+Overview:
+"""""""""
+
+Create a mask representing lanes that do or 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:
+""""""""""
+
+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.alias.lane.mask.*``' intrinsics are semantically
+equivalent to:
+
+::
+
+      %diff = (%ptrB - %ptrA) / %elementSize
+      %m[i] = (icmp ult i, %diff) || (%diff <= 0)
----------------
sdesmalen-arm wrote:

Could you add that this holds for `i = 0 to VF-1` ? (is that right?)

For some example `ptrA = 0, ptrB = 15`, and a VF = 16, this results in a mask `<1, 1, ..., 1, 0>`, which is the inverse of what the name `get.alias.lane.mask` suggests. It shows which lanes _don't_ alias. Should the behaviour be inverted or should the intrinsic be renamed?

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