Cache results of Cmts.preserve #1766
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
|
MaxRSS does not change too much when formatting |
emillon
force-pushed
the
issue1750
branch
2 times, most recently
from
aa60006 to
c3268d6
Compare
gpetiot
approved these changes
Aug 6, 2021
gpetiot
reviewed
Aug 6, 2021
lib/Fmt_ast.ml
Outdated
| type c = | ||
| { conf: Conf.t | ||
| ; debug: bool | ||
| ; source: Source.t | ||
| ; cmts: Cmts.t | ||
| ; fmt_code: Conf.t -> string -> (Fmt.t, unit) Result.t } | ||
| ; fmt_code: Conf.t -> string -> (Fmt.t, unit) Result.t | ||
| ; layout_cache: Layout_cache.t } |
There was a problem hiding this comment.
I'm not sure it's worth to add this field to the type c, as we don't need to pass it to every function, it's only used by Cmts.preserve, why not add it to Cmts.t and directly modify the implementation of Cmts.preserve?
There was a problem hiding this comment.
I did so because it's not really related to comment handling, but yes we can do that.
The `preserve` function returns a string with the layout of a part of the AST. It is used in several places to determine if a subpart has a break for example. This can be a problem when these constructions are nested, since laying out the external construction requires laying out the internal ones first, and this creates quadratic behavior. This is solved by caching the results of these intermediate layouts. This cache is unbounded so there are bad corner cases. At worst, each cached point is associated to the result string which could mean quadratic memory consumption. Some ways to fix this: - use a LRU cache like the one from `core_kernel` - store only a summary rather than the full string (length, number of lines, max indent) In addition to ocaml-ppx#1750, a similar case can be triggered using nested cases. It seems that `expression_width` would be affected but I have not been able to reproduce that using that code path. Closes ocaml-ppx#1750
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.
The
preservefunction returns a string with the layout of a part of the AST. It is used in several places to determine if a subpart has a break for example.This can be a problem when these constructions are nested, since laying out the external construction requires laying out the internal ones first, and this creates quadratic behavior.
This is solved by caching the results of these intermediate layouts. This cache is unbounded so there are bad corner cases. At worst, each cached point is associated to the result string which could mean quadratic memory consumption.
Some ways to fix this:
core_kernelIn addition to #1750, a similar case can be triggered using nested cases. It seems that
expression_widthwould be affected but I have not been able to reproduce that using that code path, so this part stays not cached.Closes #1750