Fix non-deterministic encoding of syntax contexts by aerooneqq · Pull Request #161450 · rust-lang/rust

aerooneqq · 2026-08-21T10:20:19Z

View all comments

Reiteration of #157409. Explanation can be found in comment for encoding_indices and in the issue.

Fixes #129094. Blocked by #161353.

r? @petrochenkov

No llms used.

petrochenkov · 2026-09-03T12:23:21Z

@bors try @rust-timer queue

…ing, r=<try> Fix non-deterministic encoding of syntax contexts

rust-bors · 2026-09-03T13:23:29Z

☀️ Try build successful (CI)
Build commit: 7e01adf (7e01adfdd3209974b2d32d2eb35d4173deaa540b)
Base parent: 4fcf397 (4fcf39725a9c99bd495d8c73af83628a256ff9a9)

rust-timer · 2026-09-03T14:14:37Z

Finished benchmarking commit (7e01adf): comparison URL.

Overall result: ❌ regressions - please read:

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.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.6%	[0.1%, 1.9%]	72
Regressions ❌ (secondary)	0.6%	[0.1%, 1.7%]	50
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.1%, 1.9%]	72

Max RSS (memory usage)

Results (primary 1.0%, secondary -1.6%)

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

	mean	range	count
Regressions ❌ (primary)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	3.7%	[2.6%, 4.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.7%	[-4.6%, -1.4%]	5
All ❌✅ (primary)	1.0%	[1.0%, 1.0%]	1

Cycles

Results (primary -0.2%, secondary 4.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	4.5%	[4.5%, 4.5%]	1
Improvements ✅ (primary)	-2.7%	[-2.7%, -2.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-2.7%, 2.3%]	2

Binary size

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

Bootstrap: 476.065s -> 474.462s (-0.34%)
Artifact size: 401.18 MiB -> 401.32 MiB (0.03%)

rust-bors · 2026-09-08T10:34:43Z

☀️ Try build successful (CI)
Build commit: e742195 (e74219583a992b4baebf5794a9a39804c61b478a)
Base parent: a3e94c2 (a3e94c2ff51d6fa9929cf637fd85df3975119801)

rust-timer · 2026-09-08T12:39:58Z

Finished benchmarking commit (e742195): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

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.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.2%	[0.2%, 0.2%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.3%, -0.2%]	3
Improvements ✅ (secondary)	-0.5%	[-0.8%, -0.4%]	6
All ❌✅ (primary)	-0.1%	[-0.3%, 0.2%]	5

Max RSS (memory usage)

Results (primary 0.8%, secondary -1.5%)

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

	mean	range	count
Regressions ❌ (primary)	1.7%	[0.4%, 4.4%]	4
Regressions ❌ (secondary)	5.2%	[5.2%, 5.2%]	1
Improvements ✅ (primary)	-1.0%	[-1.5%, -0.5%]	2
Improvements ✅ (secondary)	-3.2%	[-3.9%, -2.0%]	4
All ❌✅ (primary)	0.8%	[-1.5%, 4.4%]	6

Cycles

Results (primary 0.4%, secondary 4.0%)

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

	mean	range	count
Regressions ❌ (primary)	1.2%	[0.4%, 2.5%]	3
Regressions ❌ (secondary)	4.0%	[4.0%, 4.0%]	1
Improvements ✅ (primary)	-0.7%	[-1.0%, -0.5%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-1.0%, 2.5%]	5

Binary size

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

Bootstrap: 479.129s -> 477.217s (-0.40%)
Artifact size: 403.56 MiB -> 403.69 MiB (0.03%)

@petrochenkov

…nkov Refactor `HygieneEncodeContext` Some refactorings around `HygieneEncodeContext` with minor perf improvements, the most notable thing is that `Lock`s were removed. First part for rust-lang#161450. r? @petrochenkov

@petrochenkov

…nkov Refactor `HygieneEncodeContext` Some refactorings around `HygieneEncodeContext` with minor perf improvements, the most notable thing is that `Lock`s were removed. First part for rust-lang#161450. r? @petrochenkov

@petrochenkov

…nkov Refactor `HygieneEncodeContext` Some refactorings around `HygieneEncodeContext` with minor perf improvements, the most notable thing is that `Lock`s were removed. First part for rust-lang#161450. r? @petrochenkov

@petrochenkov

Refactor `HygieneEncodeContext` Some refactorings around `HygieneEncodeContext` with minor perf improvements, the most notable thing is that `Lock`s were removed. First part for #161450. r? @petrochenkov

@petrochenkov

…nkov Refactor `HygieneEncodeContext` Some refactorings around `HygieneEncodeContext` with minor perf improvements, the most notable thing is that `Lock`s were removed. First part for rust-lang#161450. r? @petrochenkov

@petrochenkov

Rollup merge of #162520 - aerooneqq:hygiene-perf, r=petrochenkov Refactor `HygieneEncodeContext` Some refactorings around `HygieneEncodeContext` with minor perf improvements, the most notable thing is that `Lock`s were removed. First part for #161450. r? @petrochenkov

rustbot · 2026-09-11T15:07:51Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

aerooneqq · 2026-09-11T15:21:45Z

@rustbot ready

petrochenkov · 2026-09-13T12:09:36Z

@bors try @rust-timer queue

…ing, r=<try> Fix non-deterministic encoding of syntax contexts

rust-bors · 2026-09-13T13:12:58Z

☀️ Try build successful (CI)
Build commit: 39a7792 (39a77924d69cd79ad293cefa28ac22d76ff9fa69)
Base parent: 98fd715 (98fd715edd3a0a5aa8f2041d7e20a3143b0fc0d3)

rust-timer · 2026-09-13T13:57:27Z

Finished benchmarking commit (39a7792): comparison URL.

Overall result: ❌ regressions - please read:

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.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.3%	[0.1%, 0.5%]	29
Regressions ❌ (secondary)	0.3%	[0.1%, 0.5%]	18
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.1%, 0.5%]	29

Max RSS (memory usage)

Results (primary -0.6%, 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
Regressions ❌ (secondary)	3.5%	[3.0%, 4.2%]	3
Improvements ✅ (primary)	-0.6%	[-0.7%, -0.5%]	2
Improvements ✅ (secondary)	-4.7%	[-8.2%, -2.7%]	3
All ❌✅ (primary)	-0.6%	[-0.7%, -0.5%]	2

Cycles

Results (secondary -5.1%)

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)	3.1%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-9.2%	[-15.3%, -3.1%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, secondary 0.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	26
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	26

Bootstrap: 492.1s -> 494.686s (0.53%)
Artifact size: 406.87 MiB -> 406.94 MiB (0.02%)

petrochenkov · 2026-09-13T14:18:27Z


            drop(mut_hctxt);

+            all_ctxt_data.sort_by_key(|(idx, _)| *idx);


Is sorting actually necessary here?
It seems like new not yet encoded contexts may already go in the sorted order.

View changes since the review

petrochenkov · 2026-09-13T14:20:25Z

+    /// however, the order of encoding is deterministic, so we can remap allocated
+    /// syntax context ids into encoding indices and use them, thus outputting
+    /// same metadata.
+    encoding_indices: FxHashMap<SyntaxContext, u32>,


We can try benchmarking IndexVec here, it's less memory efficient, but the lookup should be faster.

View changes since the review

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 21, 2026

rustbot assigned petrochenkov Aug 21, 2026

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Aug 21, 2026