stdlib: remove a wrong internal check for COW array mutation #34639
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
Don't complain if the empty array buffer singleton is set to mutable. This can happen if reserveCapacity is called with a 0-capacity for an empty array. In this case the resulting array is still the empty array singleton. For the compiler, it's safe to treat the empty array singleton as "mutable", because there is never anything written to an array with zero capacity: all mutating array operations do any form of capacity/size > 0 check in addition to the uniqueness check. Unfortunately the empty array singleton sometimes needs such special handling with is not obvious (not to say hacky). This wrong check only fired in very specific optimization scenarios, where the inliner and the COW optimizations must play together in a certain way. I could not find an isolated test case for this problem. rdar://problem/71107908
Contributor
Author
|
@swift-ci test |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
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Outdated suggestions cannot be applied.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.
Don't complain if the empty array buffer singleton is set to mutable.
This can happen if reserveCapacity is called with a 0-capacity for an empty array.
In this case the resulting array is still the empty array singleton.
For the compiler, it's safe to treat the empty array singleton as "mutable", because there is never anything written to an array with zero capacity:
all mutating array operations do any form of capacity/size > 0 check in addition to the uniqueness check.
Unfortunately the empty array singleton sometimes needs such special handling with is not obvious (not to say hacky).
This wrong check only fired in very specific optimization scenarios, where the inliner and the COW optimizations must play together in a certain way.
I could not find an isolated test case for this problem.
rdar://problem/71107908