[5.9🍒] Fix a performance issue when answering "is this tuple Copyable"? #65709
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
If we don't split up the tuple into individual constraints, we end up spending more time querying whether a tuple is Copyable in `lookupConformance`, because it will naively check the types of all elements of the tuple recursively with `lookupConformance`. This is inefficient because if we know some of the elements of the tuple are fixed types, we don't need to keep checking those again. For example, if we have `($T, Int, $U)`, and then try a binding for `$T`, we might ask again if the whole tuple conforms. Leading to `lookupConformance` to check whether `Int` (and all other elements of the tuple) conforms to Copyable, when we either already know that, or can't answer it yet because it's still a type variable. By splitting up a Copyable constraint on a tuple into invidivual constraints on each of its type elements, we can avoid this redundant work by `lookupConformance`. While today we could short-cut this even further to say that _all_ tuples are Copyable, since we emit an error if a noncopyable type appears in one, that won't be true in the near future. This is the nicer solution we'll want to keep around long-term. After discussing this with Pavel, we don't think there's a good way to add a regression test for this, because the performance issue primarily comes up in specific example programs that aren't amenable to scale tests. resolves rdar://107536402 (cherry picked from commit ce04b84)
|
@swift-ci please test |
tbkka
approved these changes
May 5, 2023
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Outdated suggestions cannot be applied.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.
• Description: This PR fixes a performance regression in a RegexBuilder test that triggered this workaround. The regression was caused by the addition of the
Copyableconstraint on generic type parameters, manifesting as a "expression too complex" error message.• Risk: Low. It's very unlikely for this change to cause regressions in typechecking other programs, based on how the solver operates.
• Original PR: #65673
• Reviewed By: @xedin
• Testing: compiler performance testing showed no regression in performance. Also manually tested different builds of the compiler to see that this patch makes the error go away. See original PR for rationale about why this is sufficient.
• Resolves: rdar://107536402