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

[Alexandre Isoard via llvm-dev]

Maybe. I can't compute the diff/patch for git though, it will have to do it
itself. Would that still work?

I am not sure I will have time to work on improving that.
For those who want to try it out I put it there:
https://reviews.llvm.org/D44244

And yes, this uses all possible forms of ugly. :-)

On Wed, Mar 7, 2018, 18:14 Jeremy Lakeman <Jeremy.Lakeman at gmail.com> wrote:

> 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
>>>
>>
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>>
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