Deal with guard contradictions caused by peeling.#2094
Merged
vext01 merged 1 commit intoykjit:masterfrom Feb 21, 2026
Merged
Conversation
When we peel we can discover that the loop isn't control-flow stable on the second iteration. If we fail to realise that, we can then optimise things incorrectly. This commit deals with that. The approach this commit takes is that, as soon as a contradiction is discovered, we abandon the peel entirely. This isn't the only thing we could do: we could (as jitc_yk used to) terminate the peel early, knowing that the final guard will always fail. I'm not sure this is worth it: the peel could end up creating extra sidetraces, and that will probably nullify whatever benefit we get from optimising the partially peeled iteration. We can revisit this later if we think it's worth it. This fixes a openresty test case, and also found a contradiction (an obvious one in retrospect!) in the unit tests.
ltratt
force-pushed
the
guard_contradictions
branch
from
d2acc39 to
cccfd4a
Compare
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
2 participants
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
When we peel we can discover that the loop isn't control-flow stable on the second iteration. If we fail to realise that, we can then optimise things incorrectly. This commit deals with that.
The approach this commit takes is that, as soon as a contradiction is discovered, we abandon the peel entirely. This isn't the only thing we could do: we could (as jitc_yk used to) terminate the peel early, knowing that the final guard will always fail. I'm not sure this is worth it: the peel could end up creating extra sidetraces, and that will probably nullify whatever benefit we get from optimising the partially peeled iteration. We can revisit this later if we think it's worth it.
This fixes a openresty test case, and also found a contradiction (an obvious one in retrospect!) in the unit tests.