Don't compile regex at every function call. #76818

hbina · 2020-09-17T02:58:15Z

Use SyncOnceCell to only compile it once.
I believe this still adds some kind of locking mechanism?

Related issue: #76817

rust-highfive · 2020-09-17T02:58:18Z

r? @ecstatic-morse

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Use `SyncOnceCell` to only compile it once. I believe this still adds some kind of locking mechanism?

ecstatic-morse · 2020-09-17T03:39:41Z

compiler/rustc_mir/src/dataflow/framework/graphviz.rs

+        static RE: SyncOnceCell<regex::Regex> = SyncOnceCell::new();
+        RE.get_or_init(|| Regex::new($re).unwrap())


It seems like this should use SyncLazy instead. @matklad is using Lazy preferable to OnceCell when possible?

Depends on code-style I guess. My preference would be to use OnceCell here, rather than lazy. I generally like to use the smallest tool for the job, and, as we are not really going to use Lazy's deref in any notable capacity here, OnceCell seems preferable.

But I also can see "don't overthink this and use just Lazy" line of thought there :-)

ecstatic-morse · 2020-09-17T03:41:26Z

compiler/rustc_mir/src/dataflow/framework/graphviz.rs

@@ -570,6 +571,13 @@ where
    }
 }

+macro_rules! regex {


I quite like this. I think it would be a good addition to the regex crate (behind a feature for now). WDYT @hbina?

I have opened an issue here rust-lang/regex#709
I am still new to this so I haven't open a PR yet.

ecstatic-morse · 2020-09-17T04:05:52Z

Here's a fun thought experiment and the reason I didn't do this earlier. The normal advice for Regex::new is to run it ahead of time and not in a tight loop. However, unlike most calls to Regex::new, this code is rarely executed. So rarely executed that I believe only a single Rust user (me) has ever done it, and I expect to continue to be able to count that number on one hand for the next few years.

While you may care that graphviz diagrams print efficiently on my machine, the vast majority of Rust users don't. In fact, they care so little that what we should probably be optimizing this code for binary size and not runtime efficiency. So while your code is indeed faster, is it smaller? The answer is probably no, although certainly not enough to matter. If anything, your time would actually be better spent making this code slower. For example, I've used argument position impl trait for io::Write when a trait object would do, and the entry point to the graphviz module should probably be #[cold]. Perhaps there's other things I'm missing?

Anyways, if you found any of that compelling feel free to work on it and I'm happy to review. Obviously, code size improvements are very marginal, and we could just merge this (modulo the switch to Lazy).

hbina · 2020-09-17T22:27:16Z

I don't think I have enough expertise to be able to make the analysis nor the call. I would like to run the tests if you could point me to the ways but this is definitely not something I am used to do.

ecstatic-morse · 2020-09-17T22:41:38Z

No worries. I'll open an issue if I get stuck waiting for something to compile. Let's just merge this as-is. If we get some clarity on the Lazy vs OnceCell issue while this is in the queue it can be updated.

@bors r+ rollup

bors · 2020-09-17T22:41:40Z

📌 Commit f4a7149 has been approved by ecstatic-morse

…me, r=ecstatic-morse Don't compile regex at every function call. Use `SyncOnceCell` to only compile it once. I believe this still adds some kind of locking mechanism? Related issue: rust-lang#76817

Rollup of 15 pull requests Successful merges: - rust-lang#76722 (Test and fix Send and Sync traits of BTreeMap artefacts) - rust-lang#76766 (Extract some intrinsics out of rustc_codegen_llvm) - rust-lang#76800 (Don't generate bootstrap usage unless it's needed) - rust-lang#76809 (simplfy condition in ItemLowerer::with_trait_impl_ref()) - rust-lang#76815 (Fix wording in mir doc) - rust-lang#76818 (Don't compile regex at every function call.) - rust-lang#76821 (Remove redundant nightly features) - rust-lang#76823 (black_box: silence unused_mut warning when building with cfg(miri)) - rust-lang#76825 (use `array_windows` instead of `windows` in the compiler) - rust-lang#76827 (fix array_windows docs) - rust-lang#76828 (use strip_prefix over starts_with and manual slicing based on pattern length (clippy::manual_strip)) - rust-lang#76840 (Move to intra doc links in core/src/future) - rust-lang#76845 (Use intra docs links in core::{ascii, option, str, pattern, hash::map}) - rust-lang#76853 (Use intra-doc links in library/core/src/task/wake.rs) - rust-lang#76871 (support panic=abort in Miri) Failed merges: r? `@ghost`

rust-highfive assigned ecstatic-morse Sep 17, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 17, 2020

Don't compile regex at every function call.

f4a7149

Use `SyncOnceCell` to only compile it once. I believe this still adds some kind of locking mechanism?

hbina force-pushed the dont_compile_regex_all_the_time branch from be14ecb to f4a7149 Compare September 17, 2020 03:04

ecstatic-morse reviewed Sep 17, 2020

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 17, 2020

rust-lang deleted a comment from bors Sep 17, 2020

RalfJung mentioned this pull request Sep 19, 2020

Rollup of 15 pull requests #76937

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Dylan-DPC-zz mentioned this pull request Sep 19, 2020

Rollup of 17 pull requests #76944

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Rollup of 18 pull requests #76945

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Rollup of 18 pull requests #76946

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Rollup of 12 pull requests #76951

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RalfJung mentioned this pull request Sep 20, 2020

Rollup of 15 pull requests #76957

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RalfJung mentioned this pull request Sep 20, 2020

Rollup of 15 pull requests #76964

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bors merged commit 3268e33 into rust-lang:master Sep 20, 2020

rustbot added this to the 1.48.0 milestone Sep 20, 2020

hbina deleted the dont_compile_regex_all_the_time branch September 20, 2020 20:15

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Don't compile regex at every function call. #76818

Don't compile regex at every function call. #76818

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bors commented Sep 17, 2020

		static RE: SyncOnceCell<regex::Regex> = SyncOnceCell::new();
		RE.get_or_init(\|\| Regex::new($re).unwrap())

Don't compile regex at every function call. #76818

Don't compile regex at every function call. #76818

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