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Add unicode fast path to is_printable #97526

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Merged
merged 1 commit into from
May 31, 2022

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Noratrieb
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@Noratrieb Noratrieb commented May 29, 2022

Before, it would enter the full expensive check even for normal ascii characters. Now, it skips the check for the ascii characters in 32..127. This range was checked manually from the current behavior.

I ran the tracing test suite in miri, and it was really slow. I looked at a profile, and miri spent most of the time in core::char::methods::escape_debug_ext, where half of that was dominated by core::unicode::printable::is_printable. So I optimized it here.

The tracing profile:
The tracing profile

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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.

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@rustbot rustbot added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label May 29, 2022
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r? @joshtriplett

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 29, 2022
@Noratrieb Noratrieb force-pushed the unicode-is-printable-fastpath branch from 4d16044 to 4b97628 Compare May 29, 2022 18:20
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Noratrieb commented May 29, 2022

I've added a new benchmark and ran it and an existing one locally, the results are promising. (write_str_macro_debug writes a single unicode character, and write_str_macro_debug_ascii writes several ascii characters to a String.)

It appears to be slightly slower for non-ascii, and a lot faster for ascii.

-- unicode-is-printable-fastpath run 1
test fmt::write_str_macro_debug                                    ... bench:     472,941 ns/iter (+/- 10,715)
test fmt::write_str_macro_debug_ascii                              ... bench:     213,816 ns/iter (+/- 17,440)

-- master run 1
test fmt::write_str_macro_debug                                    ... bench:     470,989 ns/iter (+/- 30,310)
test fmt::write_str_macro_debug_ascii                              ... bench:     352,146 ns/iter (+/- 18,440)

-- unicode-is-printable-fastpath run 2
test fmt::write_str_macro_debug                                    ... bench:     473,699 ns/iter (+/- 20,190)
test fmt::write_str_macro_debug_ascii                              ... bench:     213,746 ns/iter (+/- 11,796)

-- master run 2
test fmt::write_str_macro_debug                                    ... bench:     470,464 ns/iter (+/- 16,985)
test fmt::write_str_macro_debug_ascii                              ... bench:     348,037 ns/iter (+/- 14,689)

@Noratrieb Noratrieb force-pushed the unicode-is-printable-fastpath branch 2 times, most recently from d638586 to 1edac2d Compare May 31, 2022 06:39
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Since the conditional is needed anyway, would it be worth returning false in the < 32 case, to include that in the fast path?

Before, it would enter the full expensive check even for normal ascii
characters. Now, it skips the check for the ascii characters in
`32..127`. This range was checked manually from the current behavior.
@Noratrieb Noratrieb force-pushed the unicode-is-printable-fastpath branch from 1edac2d to 3358a41 Compare May 31, 2022 08:51
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Huh, I changed this locally but forgot to commit it.

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joshtriplett commented May 31, 2022

@bors r+ rollup=never

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bors commented May 31, 2022

📌 Commit 3358a41 has been approved by joshtriplett

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 31, 2022
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@bors rollup=never

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bors commented May 31, 2022

⌛ Testing commit 3358a41 with merge dcbd5f5...

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bors commented May 31, 2022

☀️ Test successful - checks-actions
Approved by: joshtriplett
Pushing dcbd5f5 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label May 31, 2022
@bors bors merged commit dcbd5f5 into rust-lang:master May 31, 2022
@rustbot rustbot added this to the 1.63.0 milestone May 31, 2022
@Noratrieb Noratrieb deleted the unicode-is-printable-fastpath branch May 31, 2022 12:19
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Finished benchmarking commit (dcbd5f5): comparison url.

Instruction count

  • Primary benchmarks: no relevant changes found
  • Secondary benchmarks: 🎉 relevant improvements found
mean1 max count2
Regressions 😿
(primary)
N/A N/A 0
Regressions 😿
(secondary)
N/A N/A 0
Improvements 🎉
(primary)
N/A N/A 0
Improvements 🎉
(secondary)
-0.1% -0.1% 2
All 😿🎉 (primary) N/A N/A 0

Max RSS (memory usage)

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

Cycles

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

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. number of relevant changes

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