gh-113603: Compiler no longer tries to maintain the no-empty-block invariant#113636
Merged
Conversation
iritkatriel
changed the title
…e-113054.ySwovr.rst
markshannon
approved these changes
Jan 3, 2024
markshannon
left a comment
markshannon
left a comment
Member
There was a problem hiding this comment.
Looks good. I like bug fixes that delete code.
kulikjak
pushed a commit
to kulikjak/cpython
that referenced
this pull request
Jan 22, 2024
aisk
pushed a commit
to aisk/cpython
that referenced
this pull request
Feb 11, 2024
Glyphack
pushed a commit
to Glyphack/cpython
that referenced
this pull request
Sep 2, 2024
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
In 3.12 I added some assertions that the invariants we try to maintain in the compiler are true: no empty blocks, no redundant NOPs, no redundant jumps.
The fuzzer has been managing to trip these assertions with code that (after optimization) ends up with many empty blocks (#113054 is a recent example). The problems arise when there are things like a redundant NOP, which (once removed) leaves us with an empty block, which (once removed) exposes a redundant jump.
The no-empty-blocks assertion is not actually important - an empty block doesn't spawn any code so it doesn't matter. It simplifies the compiler if we don't bother to maintain this invariant, and just handle empty blocks as we go along.