clang(-ftime-trace)优化C/C++工程编译时长

1 编译/安装ClangBuildAnalyzer

clang参数-ftime-trace需要与ClangBuildAnalyzer工具一起工作，输出每个文件的编译时长统计，首先下载ClangBuildAnalyzer：

git clone https://github.com/aras-p/ClangBuildAnalyzer.git
or
git clone https://gitee.com/wangwenchaonj/ClangBuildAnalyzer.git

编译ClangBuildAnalyzer：

cd ClangBuildAnalyzer
make -f projects/make/Makefile

将ClangBuildAnalyzer添加到系统路径：

cd build
cp ClangBuildAnalyzer /usr/local/bin/

[e-mail]:/home/~# ClangBuildAnalyzer
USAGE: one of
  ClangBuildAnalyzer --start <artifactsdir>
  ClangBuildAnalyzer --stop <artifactsdir> <filename>
  ClangBuildAnalyzer --analyze <filename>

2 待优化工程参数设置

设置clang编译器：

export CC=/usr/local/bin/clang
export CXX=/usr/local/bin/clang++

设置clang编译器-ftime-trace参数：

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -ftime-trace")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -ftime-trace")

3 编译

对ClangBuildAnalyzer源码进行编译：

mkdir build
ClangBuildAnalyzer --start ./build
make -f projects/make/Makefile
ClangBuildAnalyzer --stop ./build/ ClangBuildAnalyzer.data
ClangBuildAnalyzer --analyze ClangBuildAnalyzer.data
ls
chmod -R 777 *

4 Chrome://tracing查看编译时长统计数据

chrome://tracing只支持单个源文件的编译统计的导入，通过python脚本将所有源文件的编译统计汇总，用speedscope或chrome://tracing查看即可该工程的编译统计情况。

#!/usr/bin/env python3
"""Combine JSON from multiple -ftime-traces into one.

Run with (e.g.): python combine_traces.py foo.json bar.json.
"""

 
import json
import sys
 

if __name__ == '__main__':
    start_time = 0
    combined_data = []
    for filename in sys.argv[1:]:
        with open(filename, 'r') as f:
            file_time = None
            for event in json.load(f)['traceEvents']:
                # Skip metadata events
                # Skip total events
                # Filter out shorter events to reduce data size
                if event['ph'] == 'M' or \
                    event['name'].startswith('Total') or \
                    event['dur'] < 5000:
                    continue

                if event['name'] == 'ExecuteCompiler':
                    # Find how long this compilation takes
                    file_time = event['dur']
                    # Set the file name in ExecuteCompiler
                    event['args']['detail'] = filename
 
                # Offset start time to make compiles sequential
                event['ts'] += start_time
                # Add data to combined
                combined_data.append(event)

            # Increase the start time for the next file
            # Add 1 to avoid issues with simultaneous events
            start_time += file_time + 1

    with open('combined.json', 'w') as f:
        json.dump({'traceEvents': sorted(combined_data, key=lambda k: k['ts'])}, f)

5 参考链接

https://github.com/aras-p/ClangBuildAnalyzer/tree/v1.2.0
https://www.snsystems.com/technology/tech-blog/clang-time-trace-feature
https://aras-p.info/blog/2019/01/16/time-trace-timeline-flame-chart-profiler-for-Clang/
https://firmwaresecurity.com/2019/11/01/clang-build-analyzer-clang-build-analysis-tool/
https://aras-p.info/blog/2019/09/28/Clang-Build-Analyzer/
https://aras-p.info/blog/2019/01/12/Investigating-compile-times-and-Clang-ftime-report/
https://github.com/jlfwong/speedscope