compiler: use Tarjan's SCC algorithm to detect loops for defer #5082
+379
−45
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
Member
Author
|
I think I see what is going on here. I seem to have missed it since i ran mostly the non-device tests when developing this. The map seems to have been hiding the assignment with a nil block before. |
The compiler needs to know whether a defer is in a loop to determine whether to allocate stack or heap memory. Previously, this performed a DFS of the CFG every time a defer was found. This resulted in time complexity jointly proportional to the number of defers and the number of blocks in the function. Now, the compiler will instead use Tarjan's strongly connected components algorithm to find cycles in linear time. The search is performed lazily, so this has minimal performance impact on functions without defers. In order to implement Tarjan's SCC algorithm, additional state needed to be attached to the blocks. I chose to merge all of the per-block state into a single slice to simplify memory management.
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Outdated suggestions cannot be applied.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 compiler needs to know whether a defer is in a loop to determine whether to allocate stack or heap memory. Previously, this performed a DFS of the CFG every time a defer was found. This resulted in time complexity jointly proportional to the number of defers and the number of blocks in the function.
Now, the compiler will instead use Tarjan's strongly connected components algorithm to find cycles in linear time. The search is performed lazily, so this has minimal performance impact on functions without defers.
In order to implement Tarjan's SCC algorithm, additional state needed to be attached to the blocks. I chose to merge all of the per-block state into a single slice to simplify memory management.