Shallow resolve ty and const vars to their root vars, attempt 2 by jdonszelmann · Pull Request #158447 · rust-lang/rust

jdonszelmann · 2026-06-26T13:22:05Z

This is attempt 2. There is breakage, but how much? It may be worth it. @lcnr and I discovered today that this PR may have major perf impact on the new trait solver (in attempt 1 this wasn't tested in perf runs). In addition, fixing #158441 makes some tests 12x slower on the old solver, and this PR could mitigate that slowdown. The new solver already fixed this bug, hence we expect the new solver to become much faster with this PR.

Hence, we plan to do a crater and perf run to see just how bad it is.

rustbot · 2026-06-26T13:22:14Z

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

jdonszelmann · 2026-06-26T13:22:28Z

@bors try @rust-timer queue

…try> Shallow resolve ty and const vars to their root vars, attempt 2

rust-bors · 2026-06-26T15:29:32Z

☀️ Try build successful (CI)
Build commit: 8ac0915 (8ac0915e346f9a2e49ca3951b642c55bd7d1eaab)
Base parent: 40557f6 (40557f6225e337d68c8d4f086557ce54135f5dd9)

rust-timer · 2026-06-26T16:54:02Z

Finished benchmarking commit (8ac0915): 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
@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)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.1%]	19
Improvements ✅ (secondary)	-3.4%	[-7.5%, -0.2%]	38
All ❌✅ (primary)	-0.3%	[-0.5%, -0.1%]	19

Max RSS (memory usage)

Results (primary -0.8%, secondary 0.7%)

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)	2.3%	[2.0%, 2.8%]	3
Improvements ✅ (primary)	-0.8%	[-0.9%, -0.8%]	2
Improvements ✅ (secondary)	-4.1%	[-4.1%, -4.1%]	1
All ❌✅ (primary)	-0.8%	[-0.9%, -0.8%]	2

Cycles

Results (primary -2.3%, secondary -2.7%)

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)	5.0%	[1.5%, 10.5%]	3
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-3.8%	[-6.1%, -2.3%]	20
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Binary size

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

Bootstrap: 482.935s -> 488.862s (1.23%)
Artifact size: 392.98 MiB -> 395.55 MiB (0.65%)

lcnr · 2026-06-26T17:10:15Z

@craterbot check

craterbot · 2026-06-26T17:10:46Z

👌 Experiment pr-158447 created and queued.
🤖 Automatically detected try build 8ac0915
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-06-28T05:27:36Z

🚧 Experiment pr-158447 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-06-30T09:05:48Z

🎉 Experiment pr-158447 is completed!
📊 2 regressed and 1 fixed (997455 total)
📊 4979 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-158447/retry-regressed-list.txt ↩

theemathas · 2026-07-02T09:25:01Z

The two crater breakages are identical to #153816 and #153849. See #153869.

jdonszelmann · 2026-07-08T12:37:10Z

@bors try @rust-timer queue

rustbot · 2026-08-10T08:12:59Z

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.

lcnr · 2026-08-10T08:17:52Z

@bors r+ rollup=never

rust-bors · 2026-08-10T08:17:54Z

📌 Commit db8cf83 has been approved by lcnr

It is now in the queue for this repository.

jdonszelmann · 2026-08-10T08:51:52Z

@bors r-

rust-bors · 2026-08-10T08:51:56Z

This pull request was unapproved.

View changes since this unapproval

jdonszelmann · 2026-08-10T08:57:43Z

Apparently a test now has nicer output and better notes! awesome :)

jdonszelmann · 2026-08-10T08:58:55Z

@bors r=lcnr

rust-bors · 2026-08-10T08:58:58Z

📌 Commit 042faa5 has been approved by lcnr

It is now in the queue for this repository.

rust-bors · 2026-08-10T12:34:59Z

☀️ Test successful - CI
Approved by: lcnr
Duration: 3h 4m 50s
Pushing 7088e4b to main...

github-actions · 2026-08-10T12:38:24Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 8a2fbe3 (parent) -> 7088e4b (this PR)

Test differences

Show 6 test diffs

Stage 1

[ui (polonius)] tests/ui/coercion/fudge-inference/fudge-eager-resolve-breakage-1.rs: [missing] -> pass (J0)
[ui (polonius)] tests/ui/coercion/fudge-inference/fudge-eager-resolve-breakage-2.rs: [missing] -> pass (J0)
[ui] tests/ui/coercion/fudge-inference/fudge-eager-resolve-breakage-1.rs: [missing] -> pass (J2)
[ui] tests/ui/coercion/fudge-inference/fudge-eager-resolve-breakage-2.rs: [missing] -> pass (J2)

Stage 2

[ui] tests/ui/coercion/fudge-inference/fudge-eager-resolve-breakage-1.rs: [missing] -> pass (J1)
[ui] tests/ui/coercion/fudge-inference/fudge-eager-resolve-breakage-2.rs: [missing] -> pass (J1)

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 7088e4b63a9516ebfbfe2ab2d999cf01a528ac14 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-gnu-nopt: 1h 30m -> 2h 26m (+62.2%)
i686-gnu-2: 1h 8m -> 1h 37m (+43.5%)
dist-apple-various: 1h 22m -> 1h 53m (+37.7%)
x86_64-gnu-llvm-21-2: 1h 37m -> 1h 3m (-35.2%)
i686-gnu-nopt-1: 1h 36m -> 2h 9m (+34.0%)
dist-loongarch64-musl: 1h 49m -> 1h 15m (-30.8%)
dist-x86_64-solaris: 1h 19m -> 1h 43m (+29.8%)
dist-i686-linux: 1h 24m -> 1h 49m (+29.2%)
x86_64-gnu-distcheck: 1h 43m -> 2h 10m (+26.7%)
dist-x86_64-msvc: 1h 43m -> 2h 10m (+26.4%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2026-08-10T13:18:03Z

Finished benchmarking commit (7088e4b): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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)	-0.4%	[-0.5%, -0.2%]	11
Improvements ✅ (secondary)	-3.3%	[-7.6%, -0.5%]	43
All ❌✅ (primary)	-0.4%	[-0.5%, -0.2%]	11

Max RSS (memory usage)

Results (primary -2.4%, secondary -0.4%)

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%	[0.5%, 5.6%]	4
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-1.8%	[-6.7%, -0.4%]	13
All ❌✅ (primary)	-2.4%	[-2.4%, -2.4%]	1

Cycles

Results (primary -2.0%, secondary -2.2%)

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)	0.6%	[0.4%, 0.9%]	6
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-2.9%	[-6.7%, -0.4%]	25
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Binary size

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

Bootstrap: 454.914s -> 455.179s (0.06%)
Artifact size: 398.40 MiB -> 398.37 MiB (-0.01%)

Use `TyOrConstInferVar` in the next solver, fix #158441 This PR still has a couple percent improvement over main at time of writing (2026-08-10), as shown by the screenshot below. Rebased on #158447, should merge after since its technically required for correctness. Fixes #158441 <img width="1114" height="375" alt="image" src="https://github.com/user-attachments/assets/188a73d0-5987-48f3-923e-9883396bb1a3" /> > [!NOTE] > I've not used an LLM for any part of this PR, or any other PR I make. This includes any related work like research.

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jun 26, 2026

rustbot assigned lcnr Jun 26, 2026

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jun 26, 2026

jdonszelmann marked this pull request as ready for review June 26, 2026 13:22

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 26, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jun 26, 2026