Add fast path to `escape_string_symbol` by Kobzol · Pull Request #160453 · rust-lang/rust

Kobzol · 2026-08-03T17:14:09Z

Discussed in #159916. So far used the manual escaping variant.

CC @matthieu-m

r? the8472

Co-Authored-By: Matthieu M <matthieum.147192@gmail.com>

Kobzol · 2026-08-03T17:14:49Z

@bors try @rust-timer queue

Add fast path to `escape_string_symbol`

the8472 · 2026-08-03T17:24:28Z

Do you want it merged now and the std improvement later or do you want to wait on my PR?

Kobzol · 2026-08-03T17:26:08Z

I don't really care either way, though it would be nice to see the perf. changes separately, so I wouldn't merge both in one PR. So maybe this one first, and then your PR + switch the function back to escape_default, and ideally perf. should stay neutral.

the8472

Ok, LGTM.

r=me once perf results are back and as expected

View changes since this review

rust-bors · 2026-08-03T19:21:19Z

☀️ Try build successful (CI)
Build commit: 67829a9 (67829a9875f34c2eb6ef188686f3d7b8876dd3db)
Base parent: 7c329d6 (7c329d6c76e11ca40c5673818ab0439c1be8962c)

rust-timer · 2026-08-03T22:51:58Z

Finished benchmarking commit (67829a9): 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)	-	-	0
Improvements ✅ (secondary)	-19.2%	[-34.8%, -4.4%]	14
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.8%, secondary -2.0%)

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

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.6%, 1.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-3.8%, -1.1%]	2
Improvements ✅ (secondary)	-2.0%	[-5.5%, -0.4%]	4
All ❌✅ (primary)	-0.8%	[-3.8%, 1.0%]	4

Cycles

Results (primary -0.3%, 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)	1.0%	[0.5%, 1.8%]	3
Regressions ❌ (secondary)	0.7%	[0.4%, 1.5%]	5
Improvements ✅ (primary)	-1.0%	[-2.3%, -0.4%]	6
Improvements ✅ (secondary)	-4.4%	[-15.4%, -0.7%]	7
All ❌✅ (primary)	-0.3%	[-2.3%, 1.8%]	9

Binary size

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

Bootstrap: 491.018s -> 490.024s (-0.20%)
Artifact size: 390.29 MiB -> 391.07 MiB (0.20%)

Kobzol · 2026-08-04T05:11:36Z

@bors r=the8472

rust-bors · 2026-08-04T05:11:38Z

📌 Commit 9605762 has been approved by the8472

It is now in the queue for this repository.

Kobzol · 2026-08-04T11:00:56Z

Marking as rollup=iffy, because this only affects one benchmark, and we have a lot of rollup=never PRs in the queue.

@bors rollup=iffy

…uwer Rollup of 10 perf-sensitive pull requests Successful merges: - #157281 (perf: skip irrelevant foreign impls when building the specialization graph) - #159403 (Next steps for FnDef binder changes (instantiate most FnDef binders)) - #159763 (Optimize crate resolution for large workspace) - #160033 (Speed up `EverInitializedPlaces`) - #160268 (perf: store the fulfillment engine inline in ObligationCtxt) - #160317 (perf: Cache already-checked types in the privacy visitor) - #160399 (interpret: skip deref-projection validity checks when they are not needed) - #160451 (Deduplicate target and host filesearch) - #160453 (Add fast path to `escape_string_symbol`) - #160454 (Add offload guard flags to typeck to prevent perf regressions)

@matthieu-m

Rollup merge of #160453 - Kobzol:include-blob-opt, r=the8472 Add fast path to `escape_string_symbol` Discussed in #159916. So far used the manual escaping variant. CC @matthieu-m r? the8472

nnethercote · 2026-08-04T21:25:16Z

+        }
+    }
+
+    // Fast-path: if we don't need escaping, just return the original symbol


I swear I did this exact optimization somewhere else a long time ago.

JonathanBrouwer · 2026-08-05T06:41:27Z

Verifying that actual perf results after merge match expected results
@rust-timer build 5f46ebd

…uwer Rollup of 10 perf-sensitive pull requests Successful merges: - rust-lang/rust#157281 (perf: skip irrelevant foreign impls when building the specialization graph) - rust-lang/rust#159403 (Next steps for FnDef binder changes (instantiate most FnDef binders)) - rust-lang/rust#159763 (Optimize crate resolution for large workspace) - rust-lang/rust#160033 (Speed up `EverInitializedPlaces`) - rust-lang/rust#160268 (perf: store the fulfillment engine inline in ObligationCtxt) - rust-lang/rust#160317 (perf: Cache already-checked types in the privacy visitor) - rust-lang/rust#160399 (interpret: skip deref-projection validity checks when they are not needed) - rust-lang/rust#160451 (Deduplicate target and host filesearch) - rust-lang/rust#160453 (Add fast path to `escape_string_symbol`) - rust-lang/rust#160454 (Add offload guard flags to typeck to prevent perf regressions)

rust-timer · 2026-08-05T13:51:34Z

Finished benchmarking commit (5f46ebd): 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)	-	-	0
Improvements ✅ (secondary)	-19.2%	[-34.8%, -4.4%]	14
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.4%, secondary 0.6%)

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

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.6%, 1.1%]	6
Regressions ❌ (secondary)	0.6%	[0.4%, 1.1%]	16
Improvements ✅ (primary)	-0.7%	[-1.0%, -0.5%]	2
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.4%]	1
All ❌✅ (primary)	0.4%	[-1.0%, 1.1%]	8

Cycles

Results (primary 1.1%, secondary -4.8%)

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

	mean	range	count
Regressions ❌ (primary)	1.4%	[0.6%, 2.2%]	5
Regressions ❌ (secondary)	1.2%	[0.4%, 2.8%]	6
Improvements ✅ (primary)	-0.5%	[-0.5%, -0.5%]	1
Improvements ✅ (secondary)	-8.3%	[-20.8%, -0.4%]	10
All ❌✅ (primary)	1.1%	[-0.5%, 2.2%]	6

Binary size

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

Bootstrap: 489.577s -> 488.242s (-0.27%)
Artifact size: 390.24 MiB -> 390.27 MiB (0.01%)

Add fast path to escape_string_symbol

9605762

Co-Authored-By: Matthieu M <matthieum.147192@gmail.com>

rustbot assigned the8472 Aug 3, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 3, 2026

Kobzol mentioned this pull request Aug 3, 2026

Optimize str.escape_default().to_string() #159916

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 3, 2026

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rust-bors Bot pushed a commit that referenced this pull request Aug 3, 2026

Auto merge of #160453 - Kobzol:include-blob-opt, r=<try>

67829a9

Add fast path to `escape_string_symbol`

the8472 approved these changes Aug 3, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 3, 2026

ZuseZ4 mentioned this pull request Aug 4, 2026

Add offload guard flags to typeck to prevent perf regressions #160454

Merged

rust-bors Bot 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 Aug 4, 2026

JonathanBrouwer mentioned this pull request Aug 4, 2026

Rollup of 10 perf-sensitive pull requests #160506

Merged

rust-bors Bot merged commit 7636221 into rust-lang:main Aug 4, 2026
14 checks passed

rustbot added this to the 1.99.0 milestone Aug 4, 2026

Kobzol deleted the include-blob-opt branch August 4, 2026 16:39

nnethercote reviewed Aug 4, 2026

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rust-timer commented Aug 3, 2026

Overall result: ✅ improvements - no action needed

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Overall result: ✅ improvements - no action needed

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