[owned-phiweb-elimination] Add an "ApplySite" like wrapper for OwnershipIntroducingValues and add utilities for finding them. #30265
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
…h non-forwarding owned values at a higher level. This is a similar concept to "rc-identity" that we talk about in the low level ARC optimizer. The main idea is that all owned values in a program can be partitioned into two different kinds of values: 1. Introducer values that exist independently of any other local values in the function. It is a point of truth from which the owned objects lifetime extends from and is in a certain sense an initialization (in a category theoretic sense) in the lifetime of the underlying object that we are manipulating. 2. Forwarding values do not represent an object lifetime that is "truly" independent of any other value locally: its liveness comes from passing on liveness from some introducer or some other forwarding value. The reason why I am adding this new construct is that I am beginning to implement a new form of ARC optimization that enables us to convert @owned SIL phi arguments to @guaranteed phi arguments. As part of that, I need to have a way to in a systematic way finding the underlying incoming values (using the logic used to determine forwarding in the ownership verifier). This is the first part of that effort, defining the ontology we are going to work with. Keep in mind this is just a seed ontology, if I missed any "owned introducers" (I am sure I did), feel free to add them.
…lueIntroducers(). These enable robust walking up the def-use ossa graph to find the value that introduces an independent underlying owned value, looking through forwarding insts.
|
This isn't used anywhere now. But I am going to use it in a forthcoming commit that implements the actual mechanism here. |
|
@swift-ci smoke test and merge |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
An OwnershipIntroducingValue is a value with owned ownership that is not a result of forwarding ownership from some other value. It is similar to the notion of "rc identity" that we talk about in the low level ARC optimizer.
I am adding this support so given a specific value, we can walk up the def-use graph and find all of the ownership introducing values (what one would call in the low level ARC optimizer an "rc identity set"). As an example, consider the following SIL:
In this case, the set of ownership introducing values for
%3would be (%0, %1).In order to implement phi elimination, I need to be able to ascertain all of the owned value introducers for a specific incoming value so I can see if I can convert all of the LiveRanges associated with the incoming value could be converted to guaranteed if we could flip the phi argument.