Bound the recursion depth of heuristic size_stmt in RTLgen#519
Merged
xavierleroy merged 1 commit intomasterfrom Aug 22, 2024
Merged
Bound the recursion depth of heuristic size_stmt in RTLgen#519xavierleroy merged 1 commit intomasterfrom
size_stmt in RTLgen#519xavierleroy merged 1 commit intomasterfrom
Conversation
Limit recursive calls on if-then-else statements to avoid quadratic behaviors. Also: put a fixed upper limit on the return value of size_stmt, since large values of the size are meaningless and make the `more_likely` criterion unstable.
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
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
The
more_likelyheuristic used in the RTLgen pass takes time O(n) where n is the size of the function and is called m times, where m = O(n) is the number of if-then-else statements in the function. This can result in O(n^2) behavior.This PR avoids this problem by limiting the depth of recursive calls on if-then-else statements. It also puts a fixed upper limit on the return value of
size_stmt, since comparing the sizes of two large statements is meaningless. (The interesting case performance-wise is when one of the statements is small.)