[llvm-dev] RFC] Shrink-wrapping improvement

[Jimmy Zhongduo Lin via llvm-dev]

Hi Francis,

Thanks for getting back to me. Could you please provide more details about the problems you encounter with those tools and what improvements required to improve compact unwinding format? Most of my experience is in the mid end, but it is still surprising to me that an improved shrink wrap will break that many tools, considering the fact that gcc has a good shrink wrapping pass and shrink-wrap-separate pass.

Also, if possible, would you be able to share some performance numbers you get back then by improving shrink-wrap?

Thanks,
Jimmy

-----Original Message-----
From: Francis Visoiu Mistrih [mailto:francisvm at yahoo.com] 
Sent: Thursday, May 14, 2020 7:30 PM
To: Jimmy Zhongduo Lin <jimmy.zhongduo.lin at huawei.com>
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] RFC] Shrink-wrapping improvement

Hi Jimmy,

> On May 13, 2020, at 2:25 PM, Jimmy Zhongduo Lin via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
>  
> Sorry for bringing back such an old thread. I am interested in the latest status of the shrink wrapping pass in LLVM. I have found some active work back in 2017 from Francis Visoiu Mistrih and Kit Barton from the following links. However, it seems that all the work suddenly stops and the improvement for the existing shrink wrapping did not make it into the trunk. Is this work abandoned?

Thanks for bringing this back.

On my side, the last time I was working on this was more on the integration on the Darwin platforms. Most of these improvements break a lot of assumptions that lots of tools use (debuggers, profilers, crash reporters, unwinders, etc.). At least for Darwin, the gains we can get from such tools is a lot higher than the performance we get from improving shrink-wrapping. So first, we would need to come up with a solution to support such code out there (for example, improving the compact unwinding format), and then we can put more work into extending shrink-wrapping.

Having said that, I can probably help with discussions and reviewing patches!

Hope that helps,

— 
Francis

>  
> https://lists.llvm.org/pipermail/llvm-dev/2017-August/116131.html
> http://lists.llvm.org/pipermail/llvm-dev/2017-May/112687.html
> https://reviews.llvm.org/D41765
>  
> Thanks,
> Jimmy
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