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

[Fedor Sergeev via llvm-dev]

git-commit-after-all solution has one serious issue - it has a hardcoded 
git handling which
makes it look problematic from many angles (picking a proper git,
selecting exact way of storing information, creating repository, 
replacing the file etc etc).

Just dumping information in a way that allows easy subsequent machine 
processing
seems to be a more flexible, less cluttered and overall clean solution 
that allows to avoid
making any of "user interface" decisions mentioned above.

We need to understand why git-commit-after-all works faster than 
print-after-all.
I dont believe in magic... yet :)

And, btw, thanks for both the idea and the patch.

regards,
   Fedor.

On 03/16/2018 12:03 AM, Alexandre Isoard wrote:
> If this is faster than -print-after-all we may actually consider 
> pushing that in the code base then? (after diligent code review of 
> course)
>
> Note that it uses the same printing method as -print-after-all:
> - create a pass of the same pass kind as the pass we just ran
> - use Module::print(raw_ostream) to print (except -print-after-all 
> only print the concerned part and into stdout)
>
> If there is improvement to be done to print-after-all it might also 
> improve git-commit-after-all. (unless that only improve speed when 
> printing constructs smaller than module)
>
> In any case, it is, to me, much more usable (and extensible) than 
> -print-after-all. But requires git to be in PATH (I'm curious if that 
> works on Windows).
>
> On Thu, Mar 15, 2018 at 1:35 PM, Daniel Sanders 
> <daniel_l_sanders at apple.com <mailto:daniel_l_sanders at apple.com>> wrote:
>
>     Does https://reviews.llvm.org/D44132
>     <https://reviews.llvm.org/D44132> help at all?
>
>
>>     On 15 Mar 2018, at 09:16, Philip Reames via llvm-dev
>>     <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>
>>     The most likely answer is that the printer used by
>>     print-after-all is slow.  I know there were some changes made
>>     around passing in some form of state cache (metadata related?)
>>     and that running printers without doing so work, but are dog
>>     slow.  I suspect the print-after-all support was never updated. 
>>     Look at what we do for the normal IR emission "-S" and see if
>>     print-after-all is out of sync.
>>
>>     Philip
>>
>>
>>     On 03/15/2018 08:45 AM, Alexandre Isoard via llvm-dev wrote:
>>>     Huh. Great! 😁
>>>
>>>     I don't believe my poor excuse from earlier (else we should map
>>>     all pipes into files!), but I'm curious why we spend less time
>>>     in system mode when going through file than pipe. Maybe
>>>     /dev/null is not as efficient as we might think? I can't believe
>>>     I'm saying that...
>>>
>>>     On Thu, Mar 15, 2018, 08:25 Fedor Sergeev
>>>     <fedor.sergeev at azul.com <mailto:fedor.sergeev at azul.com>> wrote:
>>>
>>>         Well, git by itself is so focused on performance, so its not
>>>         surprising
>>>         to me that even using git add/git commit does not cause
>>>         performance penalties.
>>>
>>>
>>>     Sure, but still, I write more stuff (entire module) into a
>>>     slower destination (file). Even ignoring git execution time it's
>>>     counter intuitive.
>>>
>>>     The only difference is that while I write more, it overwrite
>>>     itself continuously, instead of being a long linear steam. I was
>>>     thinking of mmap the file instead of going through our
>>>     raw_stream, but maybe that's unnecessary then...
>>>
>>>
>>>
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>
>
>
>
> -- 
> *Alexandre Isoard*

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