[llvm-dev] Commit module to Git after each Pass

[Jeremy Lakeman via llvm-dev]

Could you format the output so that it is compatible with git fast-import?
https://www.git-scm.com/docs/git-fast-import

On Thu, Mar 8, 2018 at 2:34 AM, Alexandre Isoard via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Today it is entirely in llvm. It is even more costly than -print-after-all
> as it:
>   - print to file
>   - print the entire module (after each basic block, for basic block
> passes, it will still print the entire module where only one basic block
> changed)
>   - call git 2 times (add then commit) and wait for them to finish (I even
> save all the empty commits)
>
> The reason I print the entire module is so that git is able to
> show/compress the change properly. Then a simple git log --patch show the
> change of each pass.
>
> Ideally, the -debug output of each pass would be piped as the git commit
> message, and the passes name+options would be the commit title. But I
> didn't have time to do that.
>
> My goal was not particularly to be efficient but to be thorough so as to
> preserve the maximum of behavioral information of each pass while not
> affecting their order and behavior.
>
> You are right, there could be major speed improvement gained by doing so
> as external processing. For instance, the output would be in the format
> that git patch takes as input. Could this be a GSoC?
>
> Today I use git filter-branch + opt as a post processing tool to generate
> the reg.dot files of the region info. In any way, the feature is a breath
> of fresh air in our development here. That's why I wanted to share. It will
> quickly become my reflex to debug with it... probably because I am at ease
> with git though.
>
> On Wed, Mar 7, 2018, 06:19 Alex Bradbury <asb at asbradbury.org> wrote:
>
>> On 6 March 2018 at 18:43, Alexandre Isoard via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > Hello,
>> >
>> > I had a stupid idea recently that turned out not so stupid after all. I
>> > wanted to be able to "see" an entire pass pipeline in action to find
>> > unnecessary transformations and/or missed opportunities and generally
>> > improve the debug-ability of LLVM.
>> >
>> > So as the title suggest, I implemented an equivalent of
>> "-print-after-all"
>> > but instead of printing into stdout I dump into a file that get commit
>> into
>> > a temporary git. There are some quirks with it but it's working and is
>> > actually awesome. For example, at first sight, I see multiple time
>> lcssa and
>> > instcombine cancelling each other's work.
>> >
>> > Of course, that has a big impact on compile time when enabled, but
>> that's
>> > still practical (git being quite good at its job) when debugging.
>> >
>> > There are improvement I can make, but would you guys be interested in
>> such
>> > feature?
>>
>> Hi Alexandre. I can definitely see how it could be useful to track
>> changes through git commits, and take advantage of your favourite repo
>> history viewer to see changes. How much of your current implementation
>> is handled via modifications to LLVM vs an external helper script? For
>> instance, I might imagine trying to achieve something similar through
>> a script that parses the output of -print-after-all in order to create
>> the desired files+commits.
>>
>> Best,
>>
>> Alex
>>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180308/61b26c06/attachment.html>