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improve format impl for literals#97480

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bors merged 2 commits intorust-lang:masterfrom
conradludgate:faster-format-literals
May 30, 2022
Merged

improve format impl for literals#97480
bors merged 2 commits intorust-lang:masterfrom
conradludgate:faster-format-literals

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@conradludgate conradludgate commented May 28, 2022

The basic idea of this change can be seen here https://godbolt.org/z/MT37cWoe1.

Updates the format impl to have a fast path for string literals and the default path for regular format args.

This change will allow format!("string literal") to be used interchangably with "string literal".to_owned().

This would be relevant in the case of f!"string literal" being legal (rust-lang/rfcs#3267) in which case it would be the easiest way to create owned strings from literals, while also being just as efficient as any other impl

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rust-highfive commented May 28, 2022

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

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rust-highfive commented May 28, 2022

r? @joshtriplett

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

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 28, 2022
Noratrieb
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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 28, 2022
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joshtriplett commented May 28, 2022

@bors r+ rollup=never

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bors commented May 28, 2022

📌 Commit 738d100438d9b099fed604cfa3b1eae47a191a43 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 28, 2022
klensy
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thomcc
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@conradludgate conradludgate force-pushed the faster-format-literals branch from 738d100 to 2869092 Compare May 28, 2022 19:18
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conradludgate commented May 29, 2022

How does one re-request a review 😅

@conradludgate conradludgate force-pushed the faster-format-literals branch from 2869092 to 5dd0fe3 Compare May 29, 2022 19:54
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Dylan-DPC commented May 30, 2022

@bors r=joshtriplett

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bors commented May 30, 2022

📌 Commit 5dd0fe3 has been approved by joshtriplett

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bors commented May 30, 2022

⌛ Testing commit 5dd0fe3 with merge 4a8d2e3...

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bors commented May 30, 2022

☀️ Test successful - checks-actions
Approved by: joshtriplett
Pushing 4a8d2e3 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label May 30, 2022
@bors bors merged commit 4a8d2e3 into rust-lang:master May 30, 2022
@rustbot rustbot added this to the 1.63.0 milestone May 30, 2022
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rust-timer commented May 30, 2022

Finished benchmarking commit (4a8d2e3): comparison url.

Instruction count

  • Primary benchmarks: 😿 relevant regressions found
  • Secondary benchmarks: 🎉 relevant improvement found
mean1 max count2
Regressions 😿
(primary)		 0.4% 0.5% 4
Regressions 😿
(secondary)		 N/A N/A 0
Improvements 🎉
(primary)		 N/A N/A 0
Improvements 🎉
(secondary)		 -1.5% -1.5% 1
All 😿🎉 (primary) 0.4% 0.5% 4

Max RSS (memory usage)

Results
  • Primary benchmarks: 😿 relevant regressions found
  • Secondary benchmarks: 🎉 relevant improvements found
mean1 max count2
Regressions 😿
(primary)		 2.3% 5.7% 4
Regressions 😿
(secondary)		 N/A N/A 0
Improvements 🎉
(primary)		 N/A N/A 0
Improvements 🎉
(secondary)		 -4.6% -4.8% 2
All 😿🎉 (primary) 2.3% 5.7% 4

Cycles

Results
  • Primary benchmarks: no relevant changes found
  • Secondary benchmarks: mixed results
mean1 max count2
Regressions 😿
(primary)		 N/A N/A 0
Regressions 😿
(secondary)		 2.2% 2.2% 1
Improvements 🎉
(primary)		 N/A N/A 0
Improvements 🎉
(secondary)		 -3.0% -3.0% 1
All 😿🎉 (primary) N/A N/A 0

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

Footnotes

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

  2. number of relevant changes ↩ ↩2 ↩3

@rustbot rustbot added the perf-regression Performance regression. label May 30, 2022
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pnkfelix commented Jun 1, 2022

Visiting for weekly rustc-perf performance triage.

  • This is adding a fast-path so that format!("literal") will compile into the same code as "literal".to_owned().
  • The primary regression is solely contained to bitmaps.
  • Its possible that the regression to bitmaps is due to format!("literal") being totally unused in that code; all instances of format! there take an additional argument.
    So its possible that the extra code to check about whether to use the fast-path is slowing things down there.
  • But I personally don't believe that explanation here: Unless I'm misunderstanding the code, there is some amount of macro-expansion into multiple instances of format!, but
    most of the expanded code is going to be dominated by all the impl blocks, not the relatively few format! instances. (Unless I massively misunderstand how the macros and/or codegen and/or inlining end up linking up here.)
  • So: I don't believe the best hypothesis I have for what is happening here.
  • But I also do not think the regression here is large enough to warrant further investigation.
  • Marking as triaged.

@rustbot label: perf-regression-triaged

@rustbot rustbot added the perf-regression-triaged The performance regression has been triaged. label Jun 1, 2022
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