Integrated: 8303078: Reduce allocations when pretty printing JCTree during compilation
Christoph Dreis
duke at openjdk.org
Thu Feb 23 15:29:28 UTC 2023
On Mon, 20 Feb 2023 14:54:18 GMT, Christoph Dreis <duke at openjdk.org> wrote:
> Hi,
>
> I've been recently optimizing a few project pipelines and always noticed that their compilation step is somewhat "expensive". Zooming into the issue always revealed Lombok to be a larger contributor. Unfortunately, I can't get rid of Lombok in this customer project (before you ask).
>
> Apparently, Lombok is printing the respective `JCTree` here and there to check for type matches. I can't imagine this to be super efficient, but that's how it is at the moment.
> <img width="948" alt="image" src="https://user-images.githubusercontent.com/6304496/220134737-bd9b508c-a908-448b-b0d1-e960db28b24a.png">
>
> Anyhow, regardless of the Lombok inefficiencies I think there are some optimization opportunities in the JDK itself.
>
> 1. Overall, `Pretty.visitSelect` accounts for 8-10% of the total allocations in this project. And among those there are StringBuilder allocations coming from the following:
>
>
> public void visitSelect(JCFieldAccess tree) {
> try {
> printExpr(tree.selected, TreeInfo.postfixPrec);
> // StringBuilder allocations hiding in here.
> print("." + tree.name);
> } catch (IOException e) {
> throw new UncheckedIOException(e);
> }
> }
>
>
> This PR splits the `print` calls into two separate ones to avoid this String concatenation.
>
> ...
> printExpr(tree.selected, TreeInfo.postfixPrec);
> print('.');
> print(tree.name);
> ...
>
>
> Secondly, the `print` method takes an `Object` which seems like a good fit for another (private?) variant of it that only takes a `char`. By this we would probably avoid any eventual boxing and avoid any conversion with `Convert.escapeUnicode(s.toString())` that seems superfluous for chars like `.`, ` `, or any braces like `(`, `{` etc.
>
> This is currently a draft PR as long as the scope is not clarified. It currently only includes the necessary changes that would optimize the particular use-case. But there are more cases where e.g. the new `char` variant could be used and/or any String concatenation could be split into separate `print` calls.
>
> Let me know what you think and if I should include the other cases as well. If you think this is worthwhile, I'd appreciate if this is is sponsored. (Including creating an issue as I can't do this myself apparently. I will of course squash everything together with the proper issue ID once available.)
>
> I've contributed before, so the CLA should be signed.
>
> Cheers,
> Christoph
This pull request has now been integrated.
Changeset: 58ca711a
Author: Christoph Dreis <christoph.dreis at freenet.de>
Committer: Jonathan Gibbons <jjg at openjdk.org>
URL: https://git.openjdk.org/jdk/commit/58ca711a9751ce38ef13e8e3ba78221f87de700f
Stats: 241 lines in 2 files changed: 44 ins; 1 del; 196 mod
8303078: Reduce allocations when pretty printing JCTree during compilation
Reviewed-by: jjg, vromero
-------------
PR: https://git.openjdk.org/jdk/pull/12667
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