[docs] Clarify SIL level TBAA rules. #2147
Merged
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
|
I took a quick look. LGTM. |
| non-class-instance heap objects. | ||
| * Two values of the same class type ``$C`` may alias. Two values of | ||
| related class type ``$B`` and ``$D``, where there is a subclass | ||
| relationship between ``$B`` and ``$D``, may alias. Two values of of |
|
The previous version of this pull request was a little muddled (I had copied it in from an old document, and upon rereading I don't think it was clarifying much). I rewrote the language last night to reflect my current understanding. Hopefully it's clear now. Please review. |
|
@atrick Are these changes still relevant? |
|
This can finally be updated now that we have a formal notion of binding memory to a type. I just need a little more time to rewrite the language accordingly. |
This documentation now reflects the optimizer's reality. I'm still working on formalizing language level rules for strict aliasing. Those will be introduced in a separate doc file. There some language about alias-introducing operations. This concept existed in the old documentation but was never really implemented. This all makes sense now that we have a formal model for binding memory to a type along with specific variants of pointer_to_address that either enforce strict aliasing or permit type punning. The detailed explanation of TBAA should probably be moved into a separate optimizer document, but there isn't a good place for it yet.
|
I'm resurrecting this old documentation PR now that practice is catching up with theory. |
phausler
pushed a commit
to phausler/swift
that referenced
this pull request
Aug 8, 2016
This documentation now reflects the optimizer's reality. I'm still working on formalizing language level rules for strict aliasing. Those will be introduced in a separate doc file. There some language about alias-introducing operations. This concept existed in the old documentation but was never really implemented. This all makes sense now that we have a formal model for binding memory to a type along with specific variants of pointer_to_address that either enforce strict aliasing or permit type punning. The detailed explanation of TBAA should probably be moved into a separate optimizer document, but there isn't a good place for it yet.
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.
This was reviewed a while back by @jckarter. I'm just getting around to cleaning up the docs.