Speed up `Parser::expected_tokens` #133793

nnethercote · 2024-12-03T09:21:43Z

The constant pushing/clearing of Parser::expected_tokens during parsing is slow. This PR speeds it up greatly.

r? @estebank

nnethercote · 2024-12-03T09:21:55Z

@bors try @rust-timer queue

…, r=<try> Speed up `Parser::expected_tokens` r? `@ghost`

bors · 2024-12-03T09:23:07Z

⌛ Trying commit 0133601 with merge 4e6952e...

bors · 2024-12-03T11:07:22Z

☀️ Try build successful - checks-actions
Build commit: 4e6952e (4e6952e2fa4367d9a5ef87505fa18f0dd3fedcc4)

rust-timer · 2024-12-03T13:34:53Z

Finished benchmarking commit (4e6952e): comparison URL.

Overall result: ✅ improvements - no action needed

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 may lead to changes in compiler perf.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-2.4%, -0.2%]	211
Improvements ✅ (secondary)	-0.8%	[-2.6%, -0.1%]	101
All ❌✅ (primary)	-0.9%	[-2.4%, -0.2%]	211

Max RSS (memory usage)

Results (primary -1.2%, secondary 1.6%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	2.9%	[0.9%, 5.4%]	3
Improvements ✅ (primary)	-2.1%	[-2.3%, -1.8%]	2
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	-1.2%	[-2.3%, 0.5%]	3

Cycles

Results (primary -1.5%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.5%	[-1.5%, -1.5%]	2

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 767.333s -> 766.554s (-0.10%)
Artifact size: 332.08 MiB -> 332.14 MiB (0.02%)

rustbot · 2024-12-04T05:40:54Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

nnethercote · 2024-12-04T05:42:51Z

Best reviewed one commit at a time.

Let's re-run perf just to be sure: @bors try @rust-timer queue

…, r=<try> Speed up `Parser::expected_tokens` The constant pushing/clearing of `Parser::expected_tokens` during parsing is slow. This PR speeds it up greatly. r? `@estebank`

bors · 2024-12-04T06:13:47Z

⌛ Trying commit f5482df with merge 26060e6...

compiler/rustc_parse/src/parser/diagnostics.rs

estebank · 2024-12-04T06:18:06Z

compiler/rustc_parse/src/parser/token_type.rs

+/// We really want to keep the number of variants to 128 or fewer, sot that
+/// `TokenTypeSet` can be implemented with a `u128`.


On the one hand, we should be able to do so. On the other, I can see this becoming a point of contention with t-lang in the medium future if we push back on a feature for this reason :)

The 17 asm symbols would be a good place to cut things down if necessary. I'm a bit annoyed that they are even in there; so many of them for such a rare use case.

estebank · 2024-12-04T06:21:28Z

compiler/rustc_parse/src/parser/token_type.rs

+        // This assertion will detect if this method and the type definition get out of sync.
+        assert_eq!(token_type as u32, val);
+        token_type


Can't the function just be the as cast with a <=104 check?

No. You can convert a C-style enum to an integer with as, but you can't convert in the other direction, e.g. as per this StackOverflow answer. There are proc macros to do it, but that answer pointed out an alternative that is suitable here: transmute is fine so long as the enum is repr(uN) for some value of N. So I will do that with repr(u8), which will cut over 100 lines of code, yay.

Should we have a static assertion that all of them roundtrip? I'm always concerned about a careless future reformat breaking the bidirectional mapping.

I'd be happy for extra protection, but I'm having trouble imagining what such a static assertion would look like. Can you explain more?

Alternatively, I can go back to an explicit match. The StackOverflow answer mentioned this style:

match v { x if x == MyEnum::A as i32 => Ok(MyEnum::A), x if x == MyEnum::B as i32 => Ok(MyEnum::B), x if x == MyEnum::C as i32 => Ok(MyEnum::C), _ => Err(()), }

It requires a line for every variant, but avoids having to write a number on each line.

I'd be happy for extra protection, but I'm having trouble imagining what such a static assertion would look like. Can you explain more?

I'd forgotten that the range operation doesn't work today in const, but I was picturing something like:

const __CHECK: () = const { for i in 0..2 { assert_eq!(E::to_i32(&E::from_i32(i)), i); } };

I've gone with the guard-based version, using a macro to avoid excessive boilerplate. It doesn't rely on unsafe, and also doesn't rely on matching up the right integer with the right variant.

compiler/rustc_parse/src/parser/token_type.rs

estebank · 2024-12-04T06:29:15Z

I'll finish reviewing tomorrow

bors · 2024-12-04T07:56:59Z

☀️ Try build successful - checks-actions
Build commit: 26060e6 (26060e63f06a4dcd55fc0757eb5b0bdc8136ed3b)

bors · 2024-12-09T01:00:25Z

☔ The latest upstream changes (presumably #134039) made this pull request unmergeable. Please resolve the merge conflicts.

nnethercote · 2024-12-09T09:11:09Z

I rebased.

@estebank, are you happy with the updated final commit?

bors · 2024-12-10T02:56:48Z

☔ The latest upstream changes (presumably #129514) made this pull request unmergeable. Please resolve the merge conflicts.

nnethercote · 2024-12-10T04:07:11Z

I rebased again.

nnethercote · 2024-12-17T23:29:36Z

I rebased a third time.

bors · 2024-12-18T06:24:01Z

☔ The latest upstream changes (presumably #134243) made this pull request unmergeable. Please resolve the merge conflicts.

nnethercote · 2024-12-18T09:35:55Z

I rebased a fourth time.

bors · 2024-12-18T20:00:32Z

☔ The latest upstream changes (presumably #134470) made this pull request unmergeable. Please resolve the merge conflicts.

Because the `Token` type is similar to but different to the `TokenType` type, and the difference is important, so we want to avoid confusion.

The most significant is `check_keyword`: it now only pushes to `expected_token_types` if the keyword check fails, which matches how all the other `check` methods work. The remainder are just tweaks to make these methods more consistent with each other.

This is a naming convention used in a handful of spots in the parser for delimiters. It confused me when I first saw it a long time ago, and I've never liked it. A web search says "Bra-ket notation" exists in linear algebra but the terminology has zero prior use in a programming context, as far as I can tell. This commit changes it to `open`/`close`, which is consistent with the rest of the compiler.

The parser pushes a `TokenType` to `Parser::expected_token_types` on every call to the various `check`/`eat` methods, and clears it on every call to `bump`. Some of those `TokenType` values are full tokens that require cloning and dropping. This is a *lot* of work for something that is only used in error messages and it accounts for a significant fraction of parsing execution time. This commit overhauls `TokenType` so that `Parser::expected_token_types` can be implemented as a bitset. This requires changing `TokenType` to a C-style parameterless enum, and adding `TokenTypeSet` which uses a `u128` for the bits. (The new `TokenType` has 105 variants.) The new types `ExpTokenPair` and `ExpKeywordPair` are now arguments to the `check`/`eat` methods. This is for maximum speed. The elements in the pairs are always statically known; e.g. a `token::BinOp(token::Star)` is always paired with a `TokenType::Star`. So we now compute `TokenType`s in advance and pass them in to `check`/`eat` rather than the current approach of constructing them on insertion into `expected_token_types`. Values of these pair types can be produced by the new `exp!` macro, which is used at every `check`/`eat` call site. The macro is for convenience, allowing any pair to be generated from a single identifier. The ident/keyword filtering in `expected_one_of_not_found` is no longer necessary. It was there to account for some sloppiness in `TokenKind`/`TokenType` comparisons. The existing `TokenType` is moved to a new file `token_type.rs`, and all its new infrastructure is added to that file. There is more boilerplate code than I would like, but I can't see how to make it shorter.

Currently it relies on having the right integer for every variant, and if you add a variant you need to adjust the integers for all subsequent variants, which is a pain. This commit introduces a match guard formulation that takes advantage of the enum-to-integer conversion to avoid specifying the integer for each variant. And it does this via a macro to avoid lots of boilerplate.

nnethercote · 2024-12-18T20:47:11Z

r? @spastorino

Santiago, initial review was done by Esteban two weeks ago, who we haven't heard from since. There was some back-and-forth about the TokenType::from_u32 function, and the final commit puts it into what I think is good shape. Individual commit logs have explanations of what changes are made, and I'm happy to answer questions. Thanks!

spastorino · 2024-12-18T21:20:56Z

r=me with CI green

nnethercote · 2024-12-18T22:47:55Z

CI is green.

@bors r=spastorino

bors · 2024-12-18T22:47:57Z

📌 Commit 5ecae1b has been approved by spastorino

It is now in the queue for this repository.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 3, 2024

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bors added a commit to rust-lang-ci/rust that referenced this pull request Dec 3, 2024

Auto merge of rust-lang#133793 - nnethercote:speed-up-expected_tokens…

4e6952e

…, r=<try> Speed up `Parser::expected_tokens` r? `@ghost`

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 3, 2024

nnethercote force-pushed the speed-up-expected_tokens branch from 0133601 to f5482df Compare December 4, 2024 05:40

nnethercote marked this pull request as ready for review December 4, 2024 05:40

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nnethercote force-pushed the speed-up-expected_tokens branch 3 times, most recently from a9b457b to 4fef25f Compare December 6, 2024 03:59

nnethercote force-pushed the speed-up-expected_tokens branch from 4fef25f to f2df88c Compare December 9, 2024 09:10

nnethercote force-pushed the speed-up-expected_tokens branch from f2df88c to d124dcd Compare December 10, 2024 04:06

nnethercote mentioned this pull request Dec 11, 2024

Remove NtVis and NtTy #133436

Open

nnethercote force-pushed the speed-up-expected_tokens branch from d124dcd to 0bb4d43 Compare December 17, 2024 23:21

nnethercote force-pushed the speed-up-expected_tokens branch from 0bb4d43 to c9abbdf Compare December 18, 2024 09:35

nnethercote added 5 commits December 19, 2024 07:36

Rename Parser::expected_tokens as Parser::expected_token_types.

c1b79e0

Because the `Token` type is similar to but different to the `TokenType` type, and the difference is important, so we want to avoid confusion.

nnethercote force-pushed the speed-up-expected_tokens branch from c9abbdf to 5ecae1b Compare December 18, 2024 20:44

rustbot assigned spastorino and unassigned estebank Dec 18, 2024

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 18, 2024

		/// We really want to keep the number of variants to 128 or fewer, sot that
		/// `TokenTypeSet` can be implemented with a `u128`.

Speed up Parser::expected_tokens #133793

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Speed up Parser::expected_tokens #133793

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Overall result: ✅ improvements - no action needed

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Speed up `Parser::expected_tokens` #133793

Speed up `Parser::expected_tokens` #133793

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