Fix unsound contract equality fast check #1703
Merged
Conversation
This file contains 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
For performance reason, the contract equality checker performs a quick pointer check to see if the two terms to compare are physically equal. In this case, it used to return `true` directly, eschewing more costly recursive checks. However, this is unsound, because the same term (physically) might be in two different environments, and have two different values. This is typically the case with function application: when evaluating `f 1` and `f 2`, both terms will physically point to the body of `f`, but in a different environment. Thus, we also need to ensure that environment are equals as well in this quick check. This commit adds a fast `ptr_eq` check to the environment as well, and now checks that both terms and their respective environments are pairwise physically equals. Passing by, this commits also fix unrelated clippy warning, after the udpate to clippy 1.73.
jneem
approved these changes
Oct 29, 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Outdated suggestions cannot be applied.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.
Closes #1700.
For performance reason, the contract equality checker performs a quick pointer check to see if the two terms to compare are physically equal. In this case, it used to return
truedirectly, eschewing more costly recursive checks.However, this is unsound, because the same term (physically) might be in two different environments, and thus evaluate in fine to two different values. This is typically the case with function application: when evaluating
f 1andf 2, both terms will physically point to the body off, but in a different environment. Thus, we also need to ensure that environment are equals as well in this fast check.This commit adds a fast
ptr_eqcheck to the environment, and now checks that both terms and their respective environments are pairwise physically equals.Passing by, this commits also fix unrelated clippy warning, after the udpate to clippy 1.73.