dawn-cmake/tools/src/cmd/turbo-cov

turbo-cov

About

turbo-cov can be used by the ./tools/run cts run-cts tool, when passing the --coverage flag. turbo-cov is substantially faster at processing coverage data than using the standard LLVM tools.

Requirements

To build turbo-cov, you will need to set the CMake define the CMake flag LLVM_SOURCE_DIR to the /llvm subdirectory of a LLVM checkout. turbo-cov requires LLVM 9+.

Details

Clang provides two tools for processing coverage data:

• llvm-profdata indexes the raw .profraw coverage profile file and emits a .profdata file.
• llvm-cov further processes the .profdata file into something human readable or machine parsable.

llvm-cov provides many options, including emitting an pretty HTML file, but is remarkably slow at producing easily machine-parsable data. Fortunately the core of llvm-cov is a few hundreds of lines of code, as it relies on LLVM libraries to do the heavy lifting.

turbo-cov is a a simple llvm-cov replacement, which efficiently converts a .profdata into a simple binary stream which can be consumed by the tools/src/cov package.

File structure

turbo-cov is a trivial binary stream, which takes the tightly-packed form:

struct Root {
    uint32_t num_files;
    File file[num_files];
};
struct File {
    uint32_t name_length
    uint8_t  name_data[name_length];
    uint32_t num_segments;
    Segment  segments[num_segments];
};
struct Segment {
    // The line where this segment begins.
    uint32_t line;
    // The column where this segment begins.
    uint32_t column;
    // The execution count, or zero if no count was recorded.
    uint32_t count;
    // When 0, the segment was uninstrumented or skipped.
    uint8_t  hasCount;
}