[perf] rustdoc: Avoid re-HIR-ty-lowering tys & const args where possible by fmease · Pull Request #163217 · rust-lang/rust

fmease · 2026-09-23T14:01:00Z

_{(No LLM was or will be used by me during the entire creation process of this PR)}

fmease · 2026-09-23T14:01:11Z

rustdoc: Avoid re-HIR-ty-lowering tys & const args where possible

rust-bors · 2026-09-23T15:00:55Z

☀️ Try build successful (CI)
Build commit: bcb47ea (bcb47ead48b72b7a7467bb2a80cc83101b1aa48d)
Base parent: 9a9d194 (9a9d1946d1e119676b7a6a8a26a264061e61027d)

rust-timer · 2026-09-23T15:45:31Z

Finished benchmarking commit (bcb47ea): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@bors rollup=never rustc-perf
@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)	-1.9%	[-3.8%, -0.2%]	6
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.9%	[-3.8%, -0.2%]	6

Max RSS (memory usage)

Results (primary -2.4%, secondary -0.9%)

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

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	0.9%	[0.9%, 0.9%]	1
Improvements ✅ (primary)	-4.1%	[-4.9%, -3.3%]	2
Improvements ✅ (secondary)	-2.7%	[-2.7%, -2.7%]	1
All ❌✅ (primary)	-2.4%	[-4.9%, 1.1%]	3

Cycles

Results (primary -3.1%, secondary -7.6%)

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)	3.0%	[2.6%, 3.6%]	3
Improvements ✅ (primary)	-3.1%	[-4.5%, -1.7%]	2
Improvements ✅ (secondary)	-13.9%	[-25.6%, -4.6%]	5
All ❌✅ (primary)	-3.1%	[-4.5%, -1.7%]	2

Binary size

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

Bootstrap: 489.957s -> 487.674s (-0.47%)
Artifact size: 407.04 MiB -> 406.34 MiB (-0.17%)

fmease · 2026-09-24T07:35:09Z

The main improvement most likely comes from the change described in #162916 (comment) in PR #162916. Since that PR also makes that change (it forcibly falls out of major refactorings), I'll wait it to get merged & then re-perf this PR.

fmease · 2026-11-03T12:23:33Z

@bors try @rust-timer queue

rustdoc: Avoid re-HIR-ty-lowering tys & const args where possible

rust-bors · 2026-11-03T13:27:11Z

☀️ Try build successful (CI)
Build commit: 2403a0b (2403a0b9762650608bb90255a733d1245bf4128d)
Base parent: 6a98084 (6a98084e4a21b04504c034dfc640e35e32ab9854)

rust-timer · 2026-11-03T14:52:40Z

Finished benchmarking commit (2403a0b): 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.

@bors rollup=iffy rustc-perf
@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)	-2.3%	[-2.4%, -2.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.4%, -2.3%]	2

Max RSS (memory usage)

Results (primary -1.6%, secondary -2.3%)

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)	-1.6%	[-1.8%, -1.4%]	2
Improvements ✅ (secondary)	-2.3%	[-3.0%, -1.3%]	3
All ❌✅ (primary)	-1.6%	[-1.8%, -1.4%]	2

Cycles

Results (primary 3.4%)

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

	mean	range	count
Regressions ❌ (primary)	3.4%	[2.8%, 4.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.4%	[2.8%, 4.0%]	2

Binary size

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

Bootstrap: 482.475s -> 482.94s (0.10%)
Artifact size: 406.38 MiB -> 406.39 MiB (0.00%)

rustbot · 2026-11-03T14:58:23Z

r? @GuillaumeGomez

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Owners of files modified in this PR: rustdoc
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GuillaumeGomez · 2026-11-03T15:00:39Z

Nice improvement considering the small amount of code updated. Looking forward for the next improvements!

@bors r+

rust-bors · 2026-11-03T15:00:43Z

📌 Commit 9294c4b has been approved by GuillaumeGomez

It is now in the queue for this repository.

…uwer Rollup of 7 pull requests Successful merges: - #165416 (fix unsoundness when compiling `[diverging_const; 0]`) - #163217 ([perf] rustdoc: Avoid re-HIR-ty-lowering tys & const args where possible) - #165371 (Don't use `llvm_type` as the type of `static`s.) - #165354 (Remove `AbiAlign`) - #165357 (rustdoc: Fix invalid clean of paths when they end with `self`) - #165401 (Add codegen test for step_by(1) loop vectorization) - #165408 (LLVMRustWriteOutputFile: Check the result of runCodeGenPipeline)

Rollup merge of #163217 - fmease:rustdoc-less-re-lowering, r=GuillaumeGomez [perf] rustdoc: Avoid re-HIR-ty-lowering tys & const args where possible <sub>(No LLM was or will be used by me during the entire creation process of this PR)</sub>

…uwer Rollup of 7 pull requests Successful merges: - rust-lang/rust#165416 (fix unsoundness when compiling `[diverging_const; 0]`) - rust-lang/rust#163217 ([perf] rustdoc: Avoid re-HIR-ty-lowering tys & const args where possible) - rust-lang/rust#165371 (Don't use `llvm_type` as the type of `static`s.) - rust-lang/rust#165354 (Remove `AbiAlign`) - rust-lang/rust#165357 (rustdoc: Fix invalid clean of paths when they end with `self`) - rust-lang/rust#165401 (Add codegen test for step_by(1) loop vectorization) - rust-lang/rust#165408 (LLVMRustWriteOutputFile: Check the result of runCodeGenPipeline)

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