Merge pull request #28447 from Anemptyship:optimize/slice-layer

optimize(dnn): optimize Slice layer for strided inputs #28447 ## Description This PR optimizes the `SliceLayer` implementation for strided inputs (where `step > 1`). The original implementation used a recursive element-wise copy (`getSliceRecursive`) for any strided slice, which was extremely inefficient. This PR introduces: 1. **Parallelization**: Uses `cv::parallel_for_` to parallelize the outermost dimension of the slice operation. 2. **Memcpy Optimization**: Automatically detects "pseudo-contiguous" blocks in strided slices (e.g., slicing an outer dimension but keeping inner dimensions intact) and uses `std::memcpy` instead of scalar loops. 3. **Refactoring**: Replaces the recursive function with a dedicated `ParallelSlice` loop body. ## Impact Significant performance improvement for strided slice operations (common in detection heads, strided sampling, etc.). **Benchmark Results:** | Test Case | Before (ms) | After (ms) | Speedup | | :--- | :--- | :--- | :--- | | **Strided Axis 0** `[::2, ...]` | 1.10 | **0.02** | **~55x** | | **Strided Axis 2** `[..., ::2]` | 1.10 | **0.06** | **~18x** | | **Contiguous** (Baseline) | 0.10 | 0.10 | 1.0x (Unchanged) | ### Pull Request Readiness Checklist See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request - [x] I agree to contribute to the project under Apache 2 License. - [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV - [x] The PR is proposed to the proper branch - [x] There is a reference to the original bug report and related work - [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable Patch to opencv_extra has the same branch name. - [ ] The feature is well documented and sample code can be built with the project CMake
2026-07-29 23:33:05 +04:00 · 2026-02-07 19:17:23 +09:00
parent 371b802103
commit ca0d47c8e6
3 changed files with 417 additions and 158 deletions
@@ -0,0 +1,93 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+
+#include "perf_precomp.hpp"
+
+namespace opencv_test {
+
+struct Layer_Slice : public TestBaseWithParam<tuple<Backend, Target>>
+{
+    void test_slice(const std::vector<int>& input_shape, int axis, int begin, int end, int step = 1)
+    {
+        int backendId = get<0>(GetParam());
+        int targetId = get<1>(GetParam());
+
+        Mat data(input_shape, CV_32FC1);
+        randu(data, 0.f, 1.f);
+
+        Net net;
+        LayerParams lp;
+        lp.type = "Slice";
+        lp.name = "testLayer";
+        lp.set("axis", axis);
+
+        std::vector<int> begins(input_shape.size(), 0);
+        std::vector<int> ends = input_shape;
+        std::vector<int> steps(input_shape.size(), 1);
+
+        begins[axis] = begin;
+        ends[axis] = end;
+        steps[axis] = step;
+
+        lp.set("begin", DictValue::arrayInt(&begins[0], begins.size()));
+        lp.set("end", DictValue::arrayInt(&ends[0], ends.size()));
+        if (step != 1) {
+            lp.set("steps", DictValue::arrayInt(&steps[0], steps.size()));
+        }
+
+        int id = net.addLayerToPrev(lp.name, lp.type, lp);
+        net.connect(0, 0, id, 0);
+
+        net.setInputsNames({"data"});
+
+        // warmup
+        {
+            net.setInput(data, "data");
+            net.setPreferableBackend(backendId);
+            net.setPreferableTarget(targetId);
+            Mat out = net.forward();
+        }
+
+        TEST_CYCLE()
+        {
+            Mat res = net.forward();
+        }
+
+        SANITY_CHECK_NOTHING();
+    }
+};
+
+PERF_TEST_P_(Layer_Slice, Slice_Contiguous_Axis0)
+{
+    test_slice({64, 128, 128}, 0, 10, 54);
+}
+
+PERF_TEST_P_(Layer_Slice, Slice_Contiguous_Axis2)
+{
+    test_slice({64, 128, 128}, 2, 10, 118);
+}
+
+PERF_TEST_P_(Layer_Slice, Slice_Small_Middle)
+{
+    test_slice({32, 64, 32}, 1, 20, 40);
+}
+
+PERF_TEST_P_(Layer_Slice, Slice_Strided_Axis0_Step2)
+{
+    // Strided slice on outer axis.
+    // [64, 128, 128] -> [0:64:2, ...]
+    test_slice({64, 128, 128}, 0, 0, 64, 2);
+}
+
+PERF_TEST_P_(Layer_Slice, Slice_Strided_Axis2_Step2)
+{
+    // Strided slice on inner axis.
+    // [64, 128, 128] -> [..., 0:128:2]
+    test_slice({64, 128, 128}, 2, 0, 128, 2);
+}
+
+
+INSTANTIATE_TEST_CASE_P(/**/, Layer_Slice, dnnBackendsAndTargets(false, false, true, false, false, false, false, false));
+
+} // namespace opencv_test