Status of new pass manager work

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.

  • 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

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.

-- Sean Silva

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

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.

Do you envision a generic set mechanism or just a couple hardcoded sets?

-- Sean Silva

Honestly haven’t spent enough time looking at it to be terribly specific. This was just some ideas tossed around with Justin I’m afraid.

If this is an area you want to work on, try some things out and propose it?

Thank you for the update and for all the work on this! Having the new pass manager in place will enable a lot of powerful follow on work. This type of major rearchitecting is often a thankless job, but it's very necessary. I am really looking forward to this being done and on by default.

Philip

I may try my hand at getting a simple `preserveAllCFGAnalyses(PA)` in place
so that we at least can represent that semantic where it is needed instead
of leaving FIXME comments.

I'll leave it to you and Justin to come up with the right design, since you
guys have it all in your heads; I'm fairly clueless about this stuff.
Whatever you guys ultimately settle on you should be able to migrate to it
with a simple NFC search and replace of the `preserveAllCFGAnalyses(PA)`
calls.

-- Sean Silva