Add CPU backend testing support via KernelAbstractions

- Extended test/utils.jl to support CPU backend with KernelAbstractions.CPU() when GROUP=CPU
- Added GPUArraysCore dependency to enable testing without actual GPU hardware
- Created comprehensive CI workflow that tests CPU backend across multiple platforms
- Updated Downgrade CI to use CPU backend for compatibility testing
- Enables testing DiffEqGPU.jl algorithms on systems without GPU hardware

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: claude

.github/workflows/CI.yml

@@ -0,0 +1,79 @@
+name: CI
+on:
+  pull_request:
+    branches:
+      - master
+    paths-ignore:
+      - 'docs/**'
+  push:
+    branches:
+      - master
+    paths-ignore:
+      - 'docs/**'
+  workflow_dispatch:
+
+jobs:
+  test:
+    name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }} - ${{ matrix.group }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        version:
+          - '1.10'
+          - '1.11'
+        os:
+          - ubuntu-latest
+          - windows-latest
+          - macOS-latest
+        arch:
+          - x64
+        group:
+          - CPU
+        include:
+          # Test CUDA on Ubuntu
+          - version: '1.10'
+            os: ubuntu-latest
+            arch: x64
+            group: CUDA
+          # Test AMDGPU on Ubuntu
+          - version: '1.10'
+            os: ubuntu-latest
+            arch: x64
+            group: AMDGPU
+          # Test oneAPI on Ubuntu
+          - version: '1.10'
+            os: ubuntu-latest
+            arch: x64
+            group: oneAPI
+          # Test Metal on macOS
+          - version: '1.10'
+            os: macOS-latest
+            arch: x64
+            group: Metal
+    steps:
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v2
+        with:
+          version: ${{ matrix.version }}
+          arch: ${{ matrix.arch }}
+      - uses: julia-actions/cache@v2
+      - name: Install GPU dependencies
+        if: matrix.group == 'CUDA'
+        run: |
+          # Install CUDA toolkit for testing
+          sudo apt-get update
+          sudo apt-get install -y nvidia-cuda-toolkit
+        shell: bash
+      - uses: julia-actions/julia-buildpkg@v1
+      - uses: julia-actions/julia-runtest@v1
+        env:
+          GROUP: ${{ matrix.group }}
+      - uses: julia-actions/julia-processcoverage@v1
+        if: matrix.group == 'CPU'
+      - uses: codecov/codecov-action@v4
+        if: matrix.group == 'CPU'
+        with:
+          files: lcov.info
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: false

.github/workflows/Downgrade.yml

@@ -17,6 +17,7 @@ jobs:
       matrix:
         downgrade_mode: ['alldeps']
         julia-version: ['1.10']
+        group: ['CPU']
     steps:
       - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v2
@@ -28,4 +29,6 @@ jobs:
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
         with:
-          ALLOW_RERESOLVE: false
+          ALLOW_RERESOLVE: false
+        env:
+          GROUP: ${{ matrix.group }}

Project.toml

@@ -10,6 +10,7 @@ DiffEqBase = "2b5f629d-d688-5b77-993f-72d75c75574e"
 Distributed = "8ba89e20-285c-5b6f-9357-94700520ee1b"
 DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+GPUArraysCore = "46192b85-c4d5-4398-a991-12ede77f4527"
 KernelAbstractions = "63c18a36-062a-441e-b654-da1e3ab1ce7c"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 LinearSolve = "7ed4a6bd-45f5-4d41-b270-4a48e9bafcae"
@@ -44,6 +45,7 @@ ChainRulesCore = "1"
 DiffEqBase = "6.122"
 DocStringExtensions = "0.8, 0.9"
 ForwardDiff = "0.10, 1"
+GPUArraysCore = "0.1, 0.2"
 KernelAbstractions = "0.9"
 LinearSolve = "1.15, 2, 3"
 Metal = "0.5, 1"
@@ -62,5 +64,10 @@ oneAPI = "1.2, 2"
 [extras]
 AMDGPU = "21141c5a-9bdb-4563-92ae-f87d6854732e"
 CUDA = "052768ef-5323-5732-b1bb-66c8b64840ba"
+GPUArraysCore = "46192b85-c4d5-4398-a991-12ede77f4527"
 Metal = "dde4c033-4e86-420c-a63e-0dd931031962"
 oneAPI = "8f75cd03-7ff8-4ecb-9b8f-daf728133b1b"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[targets]
+test = ["AMDGPU", "CUDA", "GPUArraysCore", "Metal", "oneAPI", "Test"]

test/utils.jl

@@ -11,6 +11,9 @@ elseif GROUP == "oneAPI"
 elseif GROUP == "Metal"
     using Metal
     Metal.MetalBackend()
+elseif GROUP == "CPU"
+    using KernelAbstractions
+    KernelAbstractions.CPU()
 end
 
 import GPUArraysCore