[llvm] [Code Coverage] Add a tool to check test coverage of a patch (PR #71841)

[Shivam Gupta via llvm-commits]

xgupta wrote:

I realize that it is not working for unit tests. 

So wrote a separate function to run them but their profraw file is not generating at the right place/path, and has a name of default.profraw which overrides on every run of other unit tests.

And unlike unit tests of clang, llvm unit tests are not showing up with `build/bin/llvm-lit --show-tests llvm/test` which is another thing to investigate.  

But I think it should be review and commit this version and then proceed for unit tests coverage in the next step.

```
def run_modified_unit_tests(build_dir, patch_path, tests):
    """Read the patch file, identify modified and added unit test cases, and
    then execute each of these test cases."""

    try:
        # Get the list of modified and added test cases from the patch
        with open(patch_path, "r") as patch_file:
            patch_diff = patch_file.read()

        modified_tests = []

        custom_print()
        # Use regular expressions to find modified test cases with ".ll|.c|.cpp" extension
        for match in re.finditer(
            r"^\+\+\+ [ab]/(.*\.(ll|mir|mlir|fir|c|cpp|f90|s|test))$",
            patch_diff,
            re.MULTILINE,
        ):
            test_file = match.group(1)
            # Get the current working directory
            cwd = os.getcwd()

            # Build the full file path dynamically by going two steps back from cwd
            full_test_file = os.path.join(
                os.path.dirname(cwd), "llvm-project", test_file
            )

            # Extract the first three directories from the test_file path
            first_three_dirs = os.path.join(*test_file.split(os.path.sep)[:3])

            matching_test_paths = [
                test_path for test_path in tests if first_three_dirs in test_path
            ]
            if matching_test_paths:
                custom_print()
                custom_print("Unit test file in the patch:", test_file)
                custom_print("Full unit test file path:", full_test_file)
                custom_print("Matching unit test in tests:", matching_test_paths[0])

                # Capture the first matching test path
                modified_test_path = os.path.dirname(
                    os.path.dirname(matching_test_paths[0])
                )

                # Extract the file name (excluding the extension) from test_file
                file_name = os.path.splitext(os.path.basename(test_file))[0]

                # Extract the last directory name (excluding the extension) from test_file
                last_directory = os.path.splitext(
                    os.path.basename(os.path.dirname(test_file))
                )[0]

                # Add "Tests" to the last_directory
                last_directory_with_tests = f"{last_directory}Tests"

                cwd = os.getcwd()
                os.chdir(build_dir)
                subprocess.check_call(["ninja", last_directory_with_tests])
                os.chdir(cwd)

                # Check if the file name is starts with +++
                if match.group(0).startswith("+++"):
                    modified_tests.append(full_test_file)

                    # Run each modified test case
                    custom_print("")
                    custom_print("Running modified test cases:")
                    subprocess.check_call(
                        [modified_test_path, f"--gtest_filter={file_name}*"]
                    )
                    custom_print("Test case executed:", full_test_file)

        if not modified_tests:
            custom_print("No modified unit tests found in the patch.")
            return

    except subprocess.CalledProcessError as e:
        custom_print("Error while running modified tests:", e)
        sys.exit(1)

    except Exception as ex:
        custom_print("Error:", ex)
        sys.exit(1)

```




https://github.com/llvm/llvm-project/pull/71841