Optimize `rustc_lexer` #91393

Julian-Wollersberger · 2021-11-30T16:11:24Z

The cursor.first() method in rustc_lexer now calls the chars.next() method instead of chars.nth_char(0).

This allows LLVM to optimize the code better. The biggest win is that eat_while() is now fully inlined and generates better assembly. This improves the lexer's performance by 35% in a micro-benchmark I made (Lexing all 18MB of code in the compiler directory). But lexing is only a small part of the overall compilation time, so I don't know how significant it is.

Big thanks to criterion and cargo asm.

rust-highfive · 2021-11-30T16:11:27Z

r? @petrochenkov

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compiler/rustc_lexer/src/lib.rs

the8472 · 2021-11-30T17:09:24Z

@bors try @rust-timer queue

rust-timer · 2021-11-30T17:09:26Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

bors · 2021-11-30T17:09:35Z

⌛ Trying commit 89bc19127c3cd88ad0ecae2957206172993729fe with merge f5bcd39ff4304330b2f8d73eced51275ccac2db6...

bors · 2021-11-30T18:26:39Z

☀️ Try build successful - checks-actions
Build commit: f5bcd39ff4304330b2f8d73eced51275ccac2db6 (f5bcd39ff4304330b2f8d73eced51275ccac2db6)

rust-timer · 2021-11-30T18:26:41Z

Queued f5bcd39ff4304330b2f8d73eced51275ccac2db6 with parent 1c02878, future comparison URL.

rust-timer · 2021-11-30T20:35:02Z

Finished benchmarking commit (f5bcd39ff4304330b2f8d73eced51275ccac2db6): comparison url.

Summary: This change led to moderate relevant improvements 🎉 in compiler performance.

Moderate improvement in instruction counts (up to -0.9% on incr-unchanged builds of coercions)

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR led to changes in compiler perf.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf -perf-regression

compiler/rustc_lexer/src/cursor.rs

Julian-Wollersberger · 2021-11-30T22:02:17Z

Perf says it's a 0.3% to 0.9% improvement, without any regressions. That's actually better than I expected :-)

compiler/rustc_lexer/src/cursor.rs

compiler/rustc_lexer/src/lib.rs

compiler/rustc_lexer/src/cursor.rs

and optimize the iterator returned by `tokenize(). This improves lexer performance by 35%

petrochenkov · 2021-12-02T02:57:25Z

@bors r+

bors · 2021-12-02T02:57:27Z

📌 Commit 1f147a2 has been approved by petrochenkov

wooster0 · 2021-12-02T17:14:31Z

compiler/rustc_lexer/src/cursor.rs

+
+    /// Eats symbols while predicate returns true or until the end of file is reached.
+    pub(crate) fn eat_while(&mut self, mut predicate: impl FnMut(char) -> bool) {
+        // It was tried making optimized version of this for eg. line comments, but


Suggested change

// It was tried making optimized version of this for eg. line comments, but

// There was an attempt to make an optimized version of this for e.g. line comments, but

That would have worked to.
But sorry, I saw this to late.

bors · 2021-12-03T13:20:19Z

⌛ Testing commit 1f147a2 with merge 2a9e083...

bors · 2021-12-03T16:25:54Z

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 2a9e083 to master...

rust-timer · 2021-12-03T17:56:44Z

Finished benchmarking commit (2a9e083): comparison url.

Summary: This change led to moderate relevant improvements 🎉 in compiler performance.

Moderate improvement in instruction counts (up to -1.0% on incr-unchanged builds of coercions)

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

rust-highfive assigned petrochenkov Nov 30, 2021

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 30, 2021

Mark-Simulacrum reviewed Nov 30, 2021

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wooster0 reviewed Nov 30, 2021

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petrochenkov reviewed Dec 1, 2021

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petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 1, 2021

bjorn3 reviewed Dec 1, 2021

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Replace nth_char(0) with next() in cursor.first()

1f147a2

and optimize the iterator returned by `tokenize(). This improves lexer performance by 35%

Julian-Wollersberger force-pushed the lexer_optimization branch from 89bc191 to 1f147a2 Compare December 1, 2021 18:15

apiraino added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Dec 1, 2021

Julian-Wollersberger requested a review from petrochenkov December 1, 2021 22:32

petrochenkov added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 2, 2021

petrochenkov approved these changes Dec 2, 2021

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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 Dec 2, 2021

wooster0 reviewed Dec 2, 2021

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bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 3, 2021

bors merged commit 2a9e083 into rust-lang:master Dec 3, 2021

rustbot added this to the 1.59.0 milestone Dec 3, 2021

	// It was tried making optimized version of this for eg. line comments, but
	// There was an attempt to make an optimized version of this for e.g. line comments, but

Optimize rustc_lexer #91393

Optimize rustc_lexer #91393

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Optimize `rustc_lexer` #91393

Optimize `rustc_lexer` #91393