Resolver: (un)tracked borrows for `CmRefCell` made safe by unsafe speculative flag by LorrensP-2158466 · Pull Request #160510 · rust-lang/rust

LorrensP-2158466 · 2026-08-04T14:04:56Z

Implements the tracked/untracked borrowing of CmRefCell such that we do not mutate any state during speculative resolution. Made safe by an unsafe field that requires any borrows to be dropped before the flag can change.

r? @petrochenkov

petrochenkov · 2026-08-04T14:30:11Z

We already benchmarked this as a regression (due to returning CmRef from borrow and resolution), but we know that #160345 recovers most of the performance, so we can merge this separately.

LorrensP-2158466 · 2026-08-04T14:34:29Z

Unfortunately, we can't "tie" the borrow of the resolver to the CmRef because it conflicts to much. Sometimes we only require a borrow of a CmRefCell but still want to mutate the resolver it self in some way.

petrochenkov · 2026-08-04T14:41:45Z

Unfortunately, we can't "tie" the borrow of the resolver to the CmRef because it conflicts to much. Sometimes we only require a borrow of a CmRefCell but still want to mutate the resolver it self in some way.

Yeah, I expected it to be very inconvenient.

…which does tracked and untracked borrowing

LorrensP-2158466 · 2026-08-04T15:44:46Z

force-pushed to keep it at one commit, @rustbot ready.

petrochenkov · 2026-08-04T16:51:18Z

@bors r+

rust-bors · 2026-08-04T16:51:21Z

📌 Commit e0830fa has been approved by petrochenkov

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 10. This pull request will be tested once the tree is reopened.

Reason for tree closure: manually handling queue due to backlog

@petrochenkov

…ative-flag, r=petrochenkov Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag Implements the tracked/untracked borrowing of `CmRefCell` such that we do not mutate *any* state during speculative resolution. Made safe by an unsafe field that requires any borrows to be dropped before the flag can change. r? @petrochenkov

@petrochenkov

…ative-flag, r=petrochenkov Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag Implements the tracked/untracked borrowing of `CmRefCell` such that we do not mutate *any* state during speculative resolution. Made safe by an unsafe field that requires any borrows to be dropped before the flag can change. r? @petrochenkov

@petrochenkov

…ative-flag, r=petrochenkov Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag Implements the tracked/untracked borrowing of `CmRefCell` such that we do not mutate *any* state during speculative resolution. Made safe by an unsafe field that requires any borrows to be dropped before the flag can change. r? @petrochenkov

…uwer Rollup of 22 pull requests Successful merges: - #158147 (std: fix stack buffer overflow in Windows junction_point) - #159784 (Hint that memchr returns an in-bounds index) - #160130 (Select cache values to verify by key fingerprint, not value fingerprint) - #160343 (Rename `OutlivesPredicate` to `OutlivesClause`) - #160360 (Remove rustc_middle dependency on rustc_hir_pretty) - #160387 (rustc_codegen_ssa: Correctly apply the static `--jobs-backend` limit to backend parallelism) - #160422 (move mir-opt miri tests to CI logic) - #160444 (Avoid resolving path keywords outside `TypeNS`) - #160510 (Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag) - #155424 ([blocked] Link to proposed LLM policy in CONTRIBUTING and pull request template) - #158726 (std: move futex implementations into sys::sync::futex) - #159225 (Split IncrCompSession out of Session) - #159820 (Make the `rustc_unsafe_specialization_marker` attribute actually `unsafe`) - #160198 (Rework `smallest_range_containing` to handle duplicates) - #160362 (Split `SpannedTypeVisitor` into its own crate, `rustc_ty_walk`) - #160390 (autodiff: Handle slice-tailed DSTs in type trees) - #160420 (Suggest `cast_signed()` for overflowing signed integer literals) - #160520 (Add some tests for specialization) - #160522 (fix(bootstrap): Normalize the names of proc macro dependency crates) - #160531 (docs: fix typo in AllowExprMetavar comment) - #160538 (Update expect messages in tcp.rs doc examples to follow the style guide) - #160548 (bootstrap: Register `coverage-map` and `coverage-run` aliases via a separate step)

@petrochenkov

…ative-flag, r=petrochenkov Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag Implements the tracked/untracked borrowing of `CmRefCell` such that we do not mutate *any* state during speculative resolution. Made safe by an unsafe field that requires any borrows to be dropped before the flag can change. r? @petrochenkov

…uwer Rollup of 25 pull requests Successful merges: - #154585 (treat no_mangle_generic_items as hard error instead of lint warning) - #158147 (std: fix stack buffer overflow in Windows junction_point) - #160130 (Select cache values to verify by key fingerprint, not value fingerprint) - #160343 (Rename `OutlivesPredicate` to `OutlivesClause`) - #160360 (Remove rustc_middle dependency on rustc_hir_pretty) - #160387 (rustc_codegen_ssa: Correctly apply the static `--jobs-backend` limit to backend parallelism) - #160422 (move mir-opt miri tests to CI logic) - #160444 (Avoid resolving path keywords outside `TypeNS`) - #160510 (Resolver: (un)tracked borrows for `CmRefCell` made safe my unsafe speculative flag) - #155424 ([blocked] Link to proposed LLM policy in CONTRIBUTING and pull request template) - #158726 (std: move futex implementations into sys::sync::futex) - #158762 (Emit thumb code on VEX V5) - #159225 (Split IncrCompSession out of Session) - #159820 (Make the `rustc_unsafe_specialization_marker` attribute actually `unsafe`) - #160198 (Rework `smallest_range_containing` to handle duplicates) - #160362 (Split `SpannedTypeVisitor` into its own crate, `rustc_ty_walk`) - #160390 (autodiff: Handle slice-tailed DSTs in type trees) - #160420 (Suggest `cast_signed()` for overflowing signed integer literals) - #160516 (Add regression test for HRTB projection in closure) - #160520 (Add some tests for specialization) - #160522 (fix(bootstrap): Normalize the names of proc macro dependency crates) - #160523 (Add regression test for opaque type) - #160531 (docs: fix typo in AllowExprMetavar comment) - #160538 (Update expect messages in tcp.rs doc examples to follow the style guide) - #160548 (bootstrap: Register `coverage-map` and `coverage-run` aliases via a separate step)

…uwer Rollup of 25 pull requests Successful merges: - #158147 (std: fix stack buffer overflow in Windows junction_point) - #160130 (Select cache values to verify by key fingerprint, not value fingerprint) - #160343 (Rename `OutlivesPredicate` to `OutlivesClause`) - #160360 (Remove rustc_middle dependency on rustc_hir_pretty) - #160387 (rustc_codegen_ssa: Correctly apply the static `--jobs-backend` limit to backend parallelism) - #160422 (move mir-opt miri tests to CI logic) - #160444 (Avoid resolving path keywords outside `TypeNS`) - #160510 (Resolver: (un)tracked borrows for `CmRefCell` made safe by unsafe speculative flag) - #155424 ([blocked] Link to proposed LLM policy in CONTRIBUTING and pull request template) - #158726 (std: move futex implementations into sys::sync::futex) - #158762 (Emit thumb code on VEX V5) - #159225 (Split IncrCompSession out of Session) - #159820 (Make the `rustc_unsafe_specialization_marker` attribute actually `unsafe`) - #160198 (Rework `smallest_range_containing` to handle duplicates) - #160362 (Split `SpannedTypeVisitor` into its own crate, `rustc_ty_walk`) - #160390 (autodiff: Handle slice-tailed DSTs in type trees) - #160420 (Suggest `cast_signed()` for overflowing signed integer literals) - #160501 (Add bootstrap CLI snapshot test for testing miri) - #160516 (Add regression test for HRTB projection in closure) - #160520 (Add some tests for specialization) - #160522 (fix(bootstrap): Normalize the names of proc macro dependency crates) - #160523 (Add regression test for opaque type) - #160531 (docs: fix typo in AllowExprMetavar comment) - #160538 (Update expect messages in tcp.rs doc examples to follow the style guide) - #160548 (bootstrap: Register `coverage-map` and `coverage-run` aliases via a separate step)

@petrochenkov

Rollup merge of #160510 - LorrensP-2158466:res-unsafe-speculative-flag, r=petrochenkov Resolver: (un)tracked borrows for `CmRefCell` made safe by unsafe speculative flag Implements the tracked/untracked borrowing of `CmRefCell` such that we do not mutate *any* state during speculative resolution. Made safe by an unsafe field that requires any borrows to be dropped before the flag can change. r? @petrochenkov

JonathanBrouwer · 2026-08-06T20:15:02Z

@rust-timer build 26842a9

JonathanBrouwer · 2026-08-07T08:00:40Z

^ All PRs in the rollup are getting this identical regression, this is most likely a false positive

Kobzol · 2026-08-07T09:52:16Z

This benchmark result will be most likely broken for a few new NLL benchmarks, you can ignore that.

rust-timer · 2026-08-07T10:24:30Z

Finished benchmarking commit (26842a9): comparison URL.

Overall result: ❌✅ regressions and improvements - BENCHMARK(S) FAILED

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

❗ ❗ ❗ ❗ ❗
Warning ⚠️: The following benchmark(s) failed to build:

serde-1.0.219-nll
ripgrep-14.1.1-nll
Job failure
clap_derive-4.5.32-nll

❗ ❗ ❗ ❗ ❗

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)	1.0%	[0.1%, 2.6%]	28
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.6%, -0.2%]	10
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 1.4%, secondary 20.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.4%	[1.0%, 1.9%]	6
Regressions ❌ (secondary)	21.9%	[1.0%, 31.1%]	15
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	1.4%	[1.0%, 1.9%]	6

Cycles

Results (secondary 13.0%)

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)	17.8%	[4.9%, 31.8%]	14
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-9.4%	[-14.5%, -3.5%]	3
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, secondary 0.0%)

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%]	25
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	25

Bootstrap: 454.551s -> 457.088s (0.56%)
Artifact size: 399.93 MiB -> 399.06 MiB (-0.22%)

Kobzol · 2026-08-07T11:09:21Z

@rustbot label: +perf-regression-triaged

Changes in rustc-perf.

rustbot assigned petrochenkov Aug 4, 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 4, 2026

petrochenkov reviewed Aug 4, 2026

View reviewed changes

Comment thread compiler/rustc_resolve/src/imports.rs

Comment thread compiler/rustc_resolve/src/lib.rs Outdated

Comment thread compiler/rustc_resolve/src/lib.rs Outdated

Comment thread compiler/rustc_resolve/src/lib.rs Outdated

Comment thread compiler/rustc_resolve/src/lib.rs Outdated

petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 4, 2026

implement unsafe speculative flag to be used by CmRefCell::borrow, …

e0830fa

…which does tracked and untracked borrowing

LorrensP-2158466 force-pushed the res-unsafe-speculative-flag branch from 17802e1 to e0830fa Compare August 4, 2026 15:44

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 4, 2026

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 5, 2026

Rollup of 11 pull requests #160547

Closed

jhpratt mentioned this pull request Aug 5, 2026

Rollup of 16 pull requests #160549

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JonathanBrouwer mentioned this pull request Aug 5, 2026

Rollup of 22 pull requests #160554

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JonathanBrouwer mentioned this pull request Aug 5, 2026

Rollup of 25 pull requests #160557

Closed

LorrensP-2158466 changed the title ~~Resolver: (un)tracked borrows for CmRefCell made safe my unsafe speculative flag~~ Resolver: (un)tracked borrows for CmRefCell made safe by unsafe speculative flag Aug 5, 2026

JonathanBrouwer mentioned this pull request Aug 5, 2026

Rollup of 25 pull requests #160559

Merged

rust-bors Bot merged commit 82c5ef1 into rust-lang:main Aug 5, 2026
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rustbot added this to the 1.99.0 milestone Aug 5, 2026

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rustbot added the perf-regression Performance regression. label Aug 7, 2026

rustbot added the perf-regression-triaged The performance regression has been triaged. label Aug 7, 2026

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rust-timer commented Aug 7, 2026

Overall result: ❌✅ regressions and improvements - BENCHMARK(S) FAILED

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