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Speed up Parser::expected_tokens
#133793
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Speed up Parser::expected_tokens
#133793
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@bors try @rust-timer queue |
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…, r=<try> Speed up `Parser::expected_tokens` r? `@ghost`
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☀️ Try build successful - checks-actions |
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Finished benchmarking commit (4e6952e): comparison URL. Overall result: ✅ improvements - no action neededBenchmarking 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 Instruction countThis 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.
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.
CyclesResults (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.
Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 767.333s -> 766.554s (-0.10%) |
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Some changes occurred in src/tools/rustfmt cc @rust-lang/rustfmt |
Best reviewed one commit at a time. Let's re-run perf just to be sure: @bors try @rust-timer queue |
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…, 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`
/// We really want to keep the number of variants to 128 or fewer, sot that | ||
/// `TokenTypeSet` can be implemented with a `u128`. |
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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 :)
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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.
// This assertion will detect if this method and the type definition get out of sync. | ||
assert_eq!(token_type as u32, val); | ||
token_type |
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Can't the function just be the as
cast with a <=104
check?
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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.
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Should we have a static assertion that all of them roundtrip? I'm always concerned about a careless future reformat breaking the bidirectional mapping.
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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?
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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.
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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);
}
};
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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.
I'll finish reviewing tomorrow |
☀️ Try build successful - checks-actions |
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Finished benchmarking commit (26060e6): comparison URL. Overall result: ✅ improvements - no action neededBenchmarking 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 Instruction countThis 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.
Max RSS (memory usage)Results (primary -0.9%, secondary 0.8%)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.
CyclesResults (primary 1.4%, secondary 2.4%)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.
Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 767.635s -> 770.294s (0.35%) |
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I updated, adding a new commit that uses |
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☔ The latest upstream changes (presumably #134039) made this pull request unmergeable. Please resolve the merge conflicts. |
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I rebased. @estebank, are you happy with the updated final commit? |
☔ The latest upstream changes (presumably #129514) 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.
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I rebased again. |
The constant pushing/clearing of
Parser::expected_tokens
during parsing is slow. This PR speeds it up greatly.r? @estebank