cleanup and cache proof tree building

[lcnr]

There's some cruft left over from when we had deep proof trees. We never encounter overflow when evaluating proof trees. Even if the recursion limit is 0, we still only hit the overflow limit when evaluating nested goals of the root. The root goal simply inherits the root_depth of the SearchGraph.

Split evaluate_root_goal_for_proof_tree from the rest of the trait solver. This enables us to simplify the implementation of evaluate_goal_raw and the ProofTreeBuilder as we no longer need to manually track the state of the builder and can instead use separate types for that. It does require making a few internal methods into associated functions taking a delegate and a span instead of the EvalCtxt itself.

I've also split SearchGraph::evaluate_goal and SearchGraph::evaluate_root_goal_for_proof_tree for the same reason. Both functions don't actually share too much code, so by splitting them each version gets significantly easier to read.

Add a query evaluate_root_goal_for_proof_tree_raw to cache proof tree building. This requires arena allocating inspect::Probe. I've added a new type alias I::ProbeRef for this. We may need to adapt this for rust-analyzer? It would definitely be easy to remove the Copy bound here 🤔

[lcnr]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 7f35a84 (7f35a84b7d91434e46c83ca284931b8a93251b56, parent: b41634205b549a62cfa55363d1e00c4143d30033)

[rust-timer]

Finished benchmarking commit (7f35a84): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.4%	[0.0%, 0.6%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.2%	[-5.8%, -0.8%]	14
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.5%, secondary 1.2%)

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

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	3.5%	[0.9%, 10.5%]	6
Improvements ✅ (primary)	-1.2%	[-1.6%, -0.6%]	3
Improvements ✅ (secondary)	-3.4%	[-4.6%, -2.5%]	3
All ❌✅ (primary)	-0.5%	[-1.6%, 1.5%]	4

Cycles

Results (primary 2.7%, secondary -2.8%)

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

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.7%, 2.8%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-3.7%, -1.4%]	13
All ❌✅ (primary)	2.7%	[2.7%, 2.8%]	2

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 468.353s -> 465.542s (-0.60%)
Artifact size: 390.65 MiB -> 390.62 MiB (-0.01%)

[rustbot]

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

[compiler-errors]

@bors r+ rollup=never

[bors]

📌 Commit 0edb22c has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 0edb22c with merge a2c8b0b...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing a2c8b0b to master...

[github-actions]

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 f6df223 (parent) -> a2c8b0b (this PR)

Test differences

Show 2 test diffs

2 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard a2c8b0b92c14b02f0b3f96a0d5296f1090dc286b --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

1. aarch64-apple: 5368.0s -> 6870.7s (28.0%)
2. x86_64-gnu-llvm-19: 2434.2s -> 2938.5s (20.7%)
3. x86_64-rust-for-linux: 2609.8s -> 3045.6s (16.7%)
4. dist-aarch64-apple: 6143.6s -> 7088.5s (15.4%)
5. x86_64-gnu-llvm-20-1: 3254.3s -> 3710.5s (14.0%)
6. x86_64-gnu-tools: 3386.3s -> 3788.5s (11.9%)
7. aarch64-gnu-llvm-19-1: 3309.0s -> 3697.8s (11.8%)
8. x86_64-gnu-debug: 7409.2s -> 8230.8s (11.1%)
9. pr-check-2: 2188.9s -> 2427.4s (10.9%)
10. x86_64-gnu-miri: 4418.9s -> 4838.2s (9.5%)

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]

Finished benchmarking commit (a2c8b0b): 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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-5.7%, -0.1%]	15
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -1.5%, secondary 3.1%)

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%	[1.3%, 9.6%]	14
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.5%	[-1.5%, -1.5%]	1

Cycles

Results (primary 2.1%, secondary -2.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-3.8%, -1.4%]	10
All ❌✅ (primary)	2.1%	[2.1%, 2.1%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 467.107s -> 465.026s (-0.45%)
Artifact size: 388.34 MiB -> 388.33 MiB (-0.00%)