Inline Windows OsStrExt::encode_wide

[nvzqz]

User crates currently produce much more code than necessary because the optimizer fails to make assumptions about this method.

[rust-highfive]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with r? rust-lang/libs-api @rustbot label +T-libs-api -T-libs to request review from a libs-api team reviewer. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

• Stabilizing library features
• Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
• Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
• Changing public documentation in ways that create new stability guarantees
• Changing observable runtime behavior of library APIs

[rust-highfive]

r? @joshtriplett

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[nvzqz]

friendly reminder @joshtriplett

[JohnTitor]

Do you have any result that shows this inlining is helpful e.g. generated assembly?

[thomcc]

Inlining iterator constructors does tend to be beneficial, as it's required to constant fold anything having to do with the iterator, and allows propagation of checks (for example, if a length check exists prior to construction of the iterator, the compiler only knows that continues to hold if the construction of the iterator is inlined). They also tend to be small, as this one looks to be.

As a non-generic stdlib function, I wouldn't expect this to get inlined without this, and it doesn't https://rust.godbolt.org/z/4xf8d1T6h. So I think this is fine, and am going to accept it.

@bors r+

[bors]

📌 Commit 246a80c has been approved by thomcc

It is now in the queue for this repository.

[bors]

⌛ Testing commit 246a80c with merge 7d1f57a...

[bors]

☀️ Test successful - checks-actions
Approved by: thomcc
Pushing 7d1f57a to master...

[rust-timer]

Finished benchmarking commit (7d1f57a): comparison url.

Instruction count

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 😿 relevant regressions found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	1.6%	1.8%	6
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	N/A	N/A	0

Max RSS (memory usage)

Results

• Primary benchmarks: 🎉 relevant improvement found
• Secondary benchmarks: 🎉 relevant improvement found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	-2.9%	-2.9%	1
Improvements 🎉 (secondary)	-3.8%	-3.8%	1
All 😿🎉 (primary)	-2.9%	-2.9%	1

Cycles

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	2.9%	2.9%	1
Regressions 😿 (secondary)	4.5%	6.7%	2
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-3.8%	-4.5%	2
All 😿🎉 (primary)	2.9%	2.9%	1

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

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³