More register allocator improvements #1620
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
In the recent-ish rewrite of the register allocator, I didn't make use of `can_be_same_as_input: true` to keep things simple. This commit makes use of this to allow the register allocator to sometimes avoid allocating an extra register. This helps reduce overall register pressure.
This additional code is pointless in most cases and -- particularly if we hit the `swap` case -- can be quite slow. Right now, this entire loop is somewhat suboptimal, in the sense that it doesn't guarantee to find the minimal set of register moves. We can definitely do better, but it's more work than I want to think about right now.
Sometimes we have values in registers that we're going to need in the future, but they're in registers that we need to use *right now*. Previously, we spilled them immediately. This commit tries, when possible, to move those values to another register. There is more we could do to optimise this, but this still tends to reduce the number of spills and unspills, so it's already a win.
github-merge-queue
bot
removed this pull request from the merge queue due to failed status checks
We could previously accidentally spill the "dummy" value for `None`, leading to crashes. While I'm here, tidy up and clarify the specification of `None` to make it clearer when it can be used.
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Outdated suggestions cannot be applied.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.
This PR optimises the register allocator, more often moving values than spilling them.