Optimize pattern matching

[nnethercote]

These commits speed up the match-stress-enum benchmark, which is very artificial, but the changes are simple enough that it's probably worth doing.

r? @Nadrieril

[rust-highfive]

r? @wesleywiser

(rust-highfive has picked a reviewer for you, use r? to override)

[nnethercote]

r? @Nadrieril

[nnethercote]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit f432a6447dba5e33ce3e6b759d8734f84a4fffb4 with merge 1235f8bc80de02dd823a68d66eb2c97f9f50d473...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1235f8bc80de02dd823a68d66eb2c97f9f50d473 (1235f8bc80de02dd823a68d66eb2c97f9f50d473)

[rust-timer]

Queued 1235f8bc80de02dd823a68d66eb2c97f9f50d473 with parent 8b09ba6, future comparison URL.

[est31]

@nnethercote congrats to your new job! It's extremely good news for the Rust project to see that you are back 🎉 .

[rust-timer]

Finished benchmarking commit (1235f8bc80de02dd823a68d66eb2c97f9f50d473): comparison url.

Summary: This change led to very large relevant mixed results 🤷 in compiler performance.

• Very large improvement in instruction counts (up to -22.3% on full builds of match-stress-enum)
• Very large regression in instruction counts (up to 6.2% on incr-unchanged builds of inflate)

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

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 led to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

[nnethercote]

For instruction counts it's a big win on match-stress-enum and a moderate win on unicode_normalization. I think the inflate opt incr-unchanged regression is noise, I couldn't replicate it locally and this change is a small optimization to pattern matching in the front-end, with no functional change, so if there was any regression for inflate it would affect most or all of the builds and runs.

For cycles and wall-time the wins are smaller but still present.

[nnethercote]

After discussion with @Nadrieril, we decided the second commit isn't useful for real code, it's too targeted towards the highly artificial match-stress-enum. (See rust-lang/rustc-perf#792 for more about that benchmark).

[nnethercote]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 580d357 with merge b103b623e78e73e1b16c11e3abed576ec7075c1b...

[bors]

☀️ Try build successful - checks-actions
Build commit: b103b623e78e73e1b16c11e3abed576ec7075c1b (b103b623e78e73e1b16c11e3abed576ec7075c1b)

[rust-timer]

Queued b103b623e78e73e1b16c11e3abed576ec7075c1b with parent 68ca579, future comparison URL.

[rust-timer]

Finished benchmarking commit (b103b623e78e73e1b16c11e3abed576ec7075c1b): comparison url.

Summary: This change led to very large relevant mixed results 🤷 in compiler performance.

• Very large improvement in instruction counts (up to -5.3% on full builds of match-stress-enum)
• Moderate regression in instruction counts (up to 0.5% on full builds of deeply-nested-async)

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

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 led to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

[Nadrieril]

Wow big improvements for such a small change :D

@bors r+

[bors]

📌 Commit 580d357 has been approved by Nadrieril

[bors]

⌛ Testing commit 580d357 with merge 936238a...

[bors]

☀️ Test successful - checks-actions
Approved by: Nadrieril
Pushing 936238a to master...

[rust-timer]

Finished benchmarking commit (936238a): comparison url.

Summary: This change led to very large relevant mixed results 🤷 in compiler performance.

• Very large improvement in instruction counts (up to -5.3% on full builds of match-stress-enum)
• Large regression in instruction counts (up to 4.0% on incr-unchanged builds of deep-vector)

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

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression