Optimize core::char::CaseMappingIter

[Jules-Bertholet]

Godbolt says this saves a few instructions…

@rustbot label T-libs A-layout C-optimization

[rustbot]

r? @Nilstrieb

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[Noratrieb]

The changes seem fine, but this CaseMappingIter seems pretty complex for doing a simple operation. What's the performance of just using an array::IntoIter and stopping when that one sees a \0?
I did a bit of digging on the origin of this type and it seems to have been around forever (addaa5b).

[Jules-Bertholet]

@Nilstrieb That is a much better approach, adopted.

@rustbot -S-waiting-on-author S-waiting-on-review

[Noratrieb]

Thanks!
@bors r+

[bors]

📌 Commit 2f1ab2c has been approved by Nilstrieb

It is now in the queue for this repository.

[scottmcm]

Unsure: are these something that people would commonly keep in a struct? Because while I do like the array::IntoIter phrasing of this, it means that iter will be 2×usize bigger than it used to be.

Feels like probably not, more likely something they'd just use directly and toss away, rather than use partially and keep around, but figured I'd mention it just in case.

(I wish we had an ArraySize<N> type that could be smaller for small N.)

[bors]

⌛ Testing commit 2f1ab2c with merge d5d479e...

[bors]

💔 Test failed - checks-actions

[rust-log-analyzer]

The job x86_64-msvc-ext failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

-- Configuring done (37.1s)
-- Generating done (2.6s)
-- Build files have been written to: C:/a/rust/rust/build/x86_64-pc-windows-msvc/llvm/build
running: "cmake" "--build" "." "--target" "install" "--config" "Release" "--" "-j" "8"
ninja: error: build.ninja:3780: multiple outputs aren't (yet?) supported by depslog; bring this up on the mailing list if it affects you
thread 'main' panicked at C:\Users\runneradmin\.cargo\registry\src\index.crates.io-6f17d22bba15001f\cmake-0.1.48\src\lib.rs:975:5:

command did not execute successfully, got: exit code: 1

[Jules-Bertholet]

Is this just a spurious failure? https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/ninja.20build.20failing

[Noratrieb]

@bors retry #122671 (comment)

[bors]

⌛ Testing commit 2f1ab2c with merge 1c19595...

[bors]

☀️ Test successful - checks-actions
Approved by: Nilstrieb
Pushing 1c19595 to master...

[rust-timer]

Finished benchmarking commit (1c19595): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.2%, 0.2%]	1
Regressions ❌ (secondary)	1.6%	[1.6%, 1.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.2%, 0.2%]	1

Max RSS (memory usage)

Results

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)	3.9%	[3.9%, 3.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.9%	[3.9%, 3.9%]	1

Cycles

Results

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)	2.2%	[2.2%, 2.3%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results

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)	0.2%	[0.0%, 0.4%]	8
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.0%, 0.4%]	8

Bootstrap: 667.865s -> 668.406s (0.08%)
Artifact size: 315.66 MiB -> 315.93 MiB (0.09%)