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[perf experiment] remove niche from SyntaxContext - #164803

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To test whether this causes the unexpected improvement in #164425

We could also test each of those newtypes separately, but I don't think it's super important, I just want to test the hypothesis.

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 23, 2026
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@bors try

@rust-timer queue benchmarks=ctfe-stress-5,deep-vector,issue-58319,large-workspace,libc-0.2.172,tt-muncher priority=-11

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@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 23, 2026
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rust-bors Bot pushed a commit that referenced this pull request Oct 23, 2026
[perf experiment] remove niche from SyntaxContext
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☀️ Try build successful (CI)
Build commit: 1473cc4 (1473cc45f7125ef8463d90a8e27dbed8e9f4a2fa)
Base parent: a0326ca (a0326caa8961d2900534b29e10a57afcdcf65135)

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Finished benchmarking commit (1473cc4): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

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

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (secondary -2.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
-2.1% [-2.1%, -2.1%] 1
All ❌✅ (primary) - - 0

Cycles

This perf run didn't have relevant results for this metric.

Binary size

Results (primary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
-0.1% [-0.1%, -0.0%] 4
Improvements ✅
(secondary)
- - 0
All ❌✅ (primary) -0.1% [-0.1%, -0.0%] 4

Bootstrap: missing data
Artifact size: 406.42 MiB -> 406.45 MiB (0.01%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 23, 2026
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ok, let's try to remove the niche completely (newtype_index has some smaller niche by default)

@bors try

@rust-timer queue benchmarks=ctfe-stress-5,deep-vector,issue-58319,large-workspace,libc-0.2.172,tt-muncher priority=-11

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rust-bors Bot pushed a commit that referenced this pull request Oct 24, 2026
[perf experiment] remove niche from SyntaxContext
@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 24, 2026
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The job test-x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)
[WARNING] line 38: Delta is 0 for "x", maybe try to use `compare-elements-position` instead?

======== tests/rustdoc-gui/sidebar-resize-setting.goml ========

[ERROR] line 30
    at `tests/rustdoc-gui/utils.goml` line 52
    at `tests/rustdoc-gui/utils.goml` line 42: Error: The following CSS properties still don't match: [expected `block` for key `display`, found `none`]: for command `wait-for-css: ("#settings", {"display": "block"})`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/index.html>


<= doc-ui tests done: 151 succeeded, 1 failed, 0 filtered out

Error: ()

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☀️ Try build successful (CI)
Build commit: 4612f1e (4612f1e19cb049bb70062c2f9feb003716649046)
Base parent: 34228cf (34228cf7f5bdd08d320dedf008b8995dd3e743e2)

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Finished benchmarking commit (4612f1e): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
-0.1% [-0.3%, -0.1%] 3
All ❌✅ (primary) - - 0

Max RSS (memory usage)

Results (secondary 1.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
4.1% [4.1%, 4.1%] 1
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
-2.1% [-2.1%, -2.1%] 1
All ❌✅ (primary) - - 0

Cycles

This perf run didn't have relevant results for this metric.

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: missing data
Artifact size: 406.20 MiB -> 406.16 MiB (-0.01%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 24, 2026

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4 participants