Work-in-process

Code Rewriter for OpenCV Universal Intrinsic

The API of OpenCV Universal Intrinsic is introduced some compatibility-breaking changes, in order to support variable-length backends including RVV. Most code blocks written using Universal Intrinsic will need to be rewritten. However, there are more than 400 code blocks that need to be rewritten, distributed in about 50 different files. This will be a horrible work if done by manually, so we decided to develop an automatic rewriter.

We are going to create a clang-tidy plugin to match and fix the Universal Intrinsic API that needs to be rewritten.

Example

void vadd(float *a, float *b, float *c, size_t n) {
-   for (size_t i = 0; i < n; i +=  v_float32::nlanes) {
+   for (size_t i = 0; i < n; i +=  Vtraits<v_float32>::vlanes()) {
            v_float32 va = v_load(a + i);
            v_float32 vb = v_load(b + i);
-           v_float32 vc = va + vb;
+           v_float32 vc = v_add(va, vb);
            v_store(c, vc);
    }
}

Capability

Code usage	Match and Fix	Checks
v_type::nlanes	√	opencv-dev-intrin-nlanes
v_type::nlanes (constant)	only as array size	opencv-dev-intrin-nlanes
overloaded operator	√	opencv-dev-intrin-operator
v_type::lane_type	√	opencv-dev-intrin-lanetype
get0()	√	opencv-dev-intrin-get0
v_extract_n	√	opencv-dev-intrin-nlanes
v_broadcast_element	√	opencv-dev-intrin-nlanes
...

Usage

Need to compile OpenCV (with -DCMAKE_EXPORT_COMPILE_COMMANDS=ON) and LLVM (enable clang and clang-tools-extra) firstly,

and then:

# build
mkdir build && cd build
cmake .. -G Ninja -DClang_DIR=<LLVM build directory>/lib/cmake/clang
ninja

# run
<LLVM build directory>/bin/clang-tidy --load ./build/libocv_intrinsic_tidy.so opencv-dev-intrin-'--checks=-*,opencv-dev-intrin-*' -p <OpenCV build directory> ../examples/nlanes.cpp

# run and rewrite
<LLVM build directory>/bin/clang-tidy --load ./build/libocv_intrinsic_tidy.so opencv-dev-intrin-'--checks=-*,opencv-dev-intrin-*' -p <OpenCV build directory> ../examples/nlanes.cpp -fix