[llvm-dev] Status of new pass manager work

Chandler Carruth via llvm-dev llvm-dev at lists.llvm.org
Thu May 5 13:24:53 PDT 2016

On Thu, May 5, 2016 at 12:12 PM Sean Silva <chisophugis at gmail.com> wrote:

> On Thu, May 5, 2016 at 1:29 AM, Chandler Carruth via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>> Greetings folks,
>> I just wanted to post a brief update on the status of the new pass
>> manager. Philip asked me to do this at last month's social and Life
>> intervened, but he's still got a great point, so I wanted to get it out
>> there with one day to spare before he nagged me again. =D
>> I'll keep it very brief and high level. If folks have questions about
>> anything, happy to dig into it.
>> - The core framework is there. It works, and we even have CGSCC passes
>> using both Module and Function analyses with caching and everything. Yay!
>> We also have initial loop pass infrastructure thanks to Justin! Yay!
>> - The biggest missing piece of infrastructure IMO is communicating
>> invalidation information between two parts of the pass manager itself when
>> they are operating over the results of an analysis. Both the loop passes
>> and the CGSCC passes really need this. I'm currently working on this and
>> hope to finish the first cut at CGSCC stuff for this in a few days.
>> - The second biggest missing piece is a good system for managing sets of
>> related analyses for the purpose of invalidation. Justin and I have
>> discussed using designated enums that form sets, but there hasn't been a
>> lot of concrete progress here.
> Can we maybe just have a function for each "set"? e.g. you just call
> `preserveAllCFGPasses(PA)`.
> We can maybe stamp out `preserveAllCFGPasses` and any others from the .def
> file to make sure there is a single point of truth.

My preference would be to keep the participation in a set local to the
analysis implementation.

> -- Sean Silva
>> - Most of the rest is porting passes. Lots of folks have started to help
>> here which is great, but there is still likely room for help on this front.
>> Much of this is independent of the missing infrastructure fortunately. Some
>> good examples are GVN, SROA, and the LoopInfo passes. Fair warning, CGSCC
>> passes are *much* harder to port than others and interact with some of the
>> missing infrastructure. Other passes are much easier IMO.
>> There may be more that I'm missing, but hopefully this helps people have
>> an idea of where things are.
>> -Chandler
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