From 566bd197bcd97f8522c84a400877f7697de7c0ac Mon Sep 17 00:00:00 2001
From: Michel Schanen <mschanen@anl.gov>
Date: Tue, 9 Sep 2025 15:50:31 +0000
Subject: [PATCH] oneAPI-aware MPI

---
 Project.toml     |  4 ++++
 ext/OneAPIExt.jl | 27 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 ext/OneAPIExt.jl

diff --git a/Project.toml b/Project.toml
index 7e3d66252..ac4123773 100644
--- a/Project.toml
+++ b/Project.toml
@@ -34,15 +34,19 @@ Requires = "~0.5, 1.0"
 Serialization = "1"
 Sockets = "1"
 julia = "1.6"
+oneAPI = "2.1"
 
 [extensions]
 AMDGPUExt = "AMDGPU"
 CUDAExt = "CUDA"
+OneAPIExt = "oneAPI"
 
 [extras]
 AMDGPU = "21141c5a-9bdb-4563-92ae-f87d6854732e"
 CUDA = "052768ef-5323-5732-b1bb-66c8b64840ba"
+oneAPI = "8f75cd03-7ff8-4ecb-9b8f-daf728133b1b"
 
 [weakdeps]
 AMDGPU = "21141c5a-9bdb-4563-92ae-f87d6854732e"
 CUDA = "052768ef-5323-5732-b1bb-66c8b64840ba"
+oneAPI = "8f75cd03-7ff8-4ecb-9b8f-daf728133b1b"
diff --git a/ext/OneAPIExt.jl b/ext/OneAPIExt.jl
new file mode 100644
index 000000000..6891aaf43
--- /dev/null
+++ b/ext/OneAPIExt.jl
@@ -0,0 +1,27 @@
+module OneAPIExt
+
+import MPI
+isdefined(Base, :get_extension) ? (import oneAPI) : (import ..oneAPI)
+import MPI: MPIPtr, Buffer, Datatype
+
+function Base.cconvert(::Type{MPIPtr}, A::oneAPI.oneArray{T}) where T
+    A
+end
+
+function Base.unsafe_convert(::Type{MPIPtr}, X::oneAPI.oneArray{T}) where T
+    reinterpret(MPIPtr, Base.unsafe_convert(oneAPI.ZePtr{T}, X))
+end
+
+# only need to define this for strided arrays: all others can be handled by generic machinery
+function Base.unsafe_convert(::Type{MPIPtr}, V::SubArray{T,N,P,I,true}) where {T,N,P<:oneAPI.oneArray,I}
+    X = parent(V)
+    pX = Base.unsafe_convert(oneAPI.ZePtr{T}, X)
+    pV = pX + ((V.offset1 + V.stride1) - first(LinearIndices(X)))*sizeof(T)
+    return reinterpret(MPIPtr, pV)
+end
+
+function Buffer(arr::oneAPI.oneArray)
+    Buffer(arr, Cint(length(arr)), Datatype(eltype(arr)))
+end
+
+end # OneAPIExt