Add a way to measure incremental rebuilds

[BenFrantzDale]

To me, the most important thing isn't how long a full build takes, but rather an incremental build. For example, over the course of the day, as I switch branches, rebase, bisect, etc. I'd love to be able to see stats representing that.

My mental model of ClangBuildAnalyzer is that --start puts a file in the build dir, and that --stop then searches the build dir for all .cpp.json files newer than the "start" file, and analyzes them. Likewise --all just looks at all of them.

To get what I want, I think I'd need to run a script every time I build that...

1. Searches the build dir for .cpp.json files and
2. copies them to an output folder as $(sha1sum foo.cpp.json).cpp.json.
   So for example, if I rebuilt foo.cpp three times, I would have three separate .cpp.json files, once for each build.
   Then I'd run CalngBuildAnalyzer on that output folder to find out where my time waiting for builds has actually gone over the course of the day.

Should that work? Is there interest in this?

[aras-p]

Not sure I understand the issue. Wouldn't this just work?

• ClangBuildAnalyzer --start
• do your incremental build
• ClangBuildAnalyzer --stop, and then --analyze

[BenFrantzDale]

Not sure I understand the issue. Wouldn't this just work?

• ClangBuildAnalyzer --start
• do your incremental build
• ClangBuildAnalyzer --stop, and then --analyze

Won’t that only give me stats for the most-recent build for each translation units?

[aras-p]

Oh, so you want a total sum of all the incremental builds, not only one of them. Hmm I guess copying files around like you outlined might work. Not sure if I see a need for a built-in feature like that though.

[BenFrantzDale]

Yeah. I suppose another way to address this would be to add a flag to clang like -ftime-trace=append so it keeps appending to the .cpp.json files. I don’t know if the file format supports it.

Should it work, though, if I write a script that scrapes my build dir for the json files and dumps them into one other directory of just json files named with their hash and then always run that script before every incremental rebuild and then run ClangBuildAnalyzer on that flat directory of .cpp.json files named by hash?