Rewrite Windows compat_fn macro

[ChrisDenton]

This allows using most delay loaded functions before the init code initializes them. It also only preloads a select few functions, rather than all functions.

This is optimized for the common case where a function is used after already being loaded (or failed to load). The only change in codegen at the call site is to use an atomic load instead of a plain load, which should have negligible or no impact.

I've split the old compat_fn macro in two so as not to mix two different use cases. If/when Windows 7 support is dropped compat_fn_optional can be removed entirely.

r? rust-lang/libs

[rustbot]

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 @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. 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.

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[ChrisDenton]

Hm, I'm not sure who best to review this. The diff for compat.rs isn't particularly helpful so it might be best reviewed as a new thing. Maybe...

r? @Mark-Simulacrum

But feel very free to re-roll.

[Mark-Simulacrum]

r=me with some squashing

@bors rollup=iffy

[ChrisDenton]

@bors r=Mark-Simulacrum

[bors]

📌 Commit 698d4a8 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

⌛ Testing commit 698d4a8 with merge 9f9b76c027709b96b04ceadc2c19588248755cb3...

[bors]

💥 Test timed out

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

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

[ChrisDenton]

@bors retry dist-aarch64-apple spurious timeout

[bors]

⌛ Testing commit 698d4a8 with merge 76822a2...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 76822a2 to master...

[rust-highfive]

📣 Toolstate changed by #99553!

Tested on commit 76822a2.
Direct link to PR: #99553

💔 miri on windows: test-pass → test-fail (cc @oli-obk @RalfJung).

[rust-timer]

Finished benchmarking commit (76822a2): comparison url.

Instruction count

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

Max RSS (memory usage)

Results

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	3.1%	3.1%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.4%	-3.0%	2
All 😿🎉 (primary)	N/A	N/A	0

Cycles

Results

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

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	3.2%	3.2%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	N/A	N/A	0

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

2. number of relevant changes ↩ ↩²