Fix Linear3D Indexing if Iteration Space Rank < 3

The Linear3D launch config setup did not pad its work_items lambda with ones if the iteration space rank was less than three. This MR fixes and tests this behavior.

src/pystencils/codegen/gpu_indexing.py

@@ -267,6 +267,11 @@ class GpuIndexing:
                 f" for a {rank}-dimensional kernel."
             )
 
+        work_items_expr += tuple(
+            self._ast_factory.parse_index(1)
+            for _ in range(3 - rank)
+        )
+        
         num_work_items = cast(
             _Dim3Lambda,
             tuple(self._kernel_factory.create_lambda(wit) for wit in work_items_expr),

tests/kernelcreation/test_gpu.py

@@ -31,7 +31,7 @@ except ImportError:
 @pytest.mark.parametrize("indexing_scheme", ["linear3d", "blockwise4d"])
 @pytest.mark.parametrize("omit_range_check", [False, True])
 @pytest.mark.parametrize("manual_grid", [False, True])
-def test_indexing_options(
+def test_indexing_options_3d(
     indexing_scheme: str, omit_range_check: bool, manual_grid: bool
 ):
     src, dst = fields("src, dst: [3D]")
@@ -76,6 +76,52 @@ def test_indexing_options(
     cp.testing.assert_allclose(dst_arr, expected)
 
 
+@pytest.mark.parametrize("indexing_scheme", ["linear3d", "blockwise4d"])
+@pytest.mark.parametrize("omit_range_check", [False, True])
+@pytest.mark.parametrize("manual_grid", [False, True])
+def test_indexing_options_2d(
+    indexing_scheme: str, omit_range_check: bool, manual_grid: bool
+):
+    src, dst = fields("src, dst: [2D]")
+    asm = Assignment(
+        dst.center(),
+        src[-1, 0]
+        + src[1, 0]
+        + src[0, -1]
+        + src[0, 1]
+    )
+
+    cfg = CreateKernelConfig(target=Target.CUDA)
+    cfg.gpu.indexing_scheme = indexing_scheme
+    cfg.gpu.omit_range_check = omit_range_check
+    cfg.gpu.manual_launch_grid = manual_grid
+
+    ast = create_kernel(asm, cfg)
+    kernel = ast.compile()
+
+    src_arr = cp.ones((18, 42))
+    dst_arr = cp.zeros_like(src_arr)
+
+    if manual_grid:
+        match indexing_scheme:
+            case "linear3d":
+                kernel.launch_config.block_size = (10, 8, 1)
+                kernel.launch_config.grid_size = (4, 2, 1)
+            case "blockwise4d":
+                kernel.launch_config.block_size = (40, 1, 1)
+                kernel.launch_config.grid_size = (16, 1, 1)
+
+    elif indexing_scheme == "linear3d":
+        kernel.launch_config.block_size = (10, 8, 1)
+
+    kernel(src=src_arr, dst=dst_arr)
+
+    expected = cp.zeros_like(src_arr)
+    expected[1:-1, 1:-1].fill(4.0)
+
+    cp.testing.assert_allclose(dst_arr, expected)
+
+
 def test_invalid_indexing_schemes():
     src, dst = fields("src, dst: [4D]")
     asm = Assignment(src.center(0), dst.center(0))