Improve caching by introducing TypingMode::ErasedNotCoherence

[jdonszelmann]

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r? @lcnr

This introduces TypingMode::ErasedNotCoherence. Most typing modes contain a list of opaque types, which are quite often unused during canonicalization. With this change, any time we try canonicalization, we replace whichever typing mode we're currently in with ErasedNotcoherence, attempt to canonicalize, and if that fails retry in the original typing mode. If erased mode succeeds, this is beneficial because that way the opaque types don't end up in the cache key, allowing more cache reuse.

This seems to have a small (0.5%) slowdown on most programs, but a dramatic (>60%) speedup in specific cases like the rustc-perf wg-grammar benchmark. Some more improvements are expected with "eager normalization", which is work that's under way right now.

[jdonszelmann]

@bors try

[jdonszelmann]

@bors try parent=14196dbfa3eb7c30195251eac092b1b86c8a2d84

[jdonszelmann]

@rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: db1df07 (db1df07682e37be559858ab003b949a2c17b5b3b, parent: 14196dbfa3eb7c30195251eac092b1b86c8a2d84)

[rust-timer]

Finished benchmarking commit (db1df07): 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
@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)	0.8%	[0.2%, 1.8%]	11
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.6%	[-1.0%, -0.2%]	2
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.9%, secondary 1.7%)

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

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	1.7%	[1.0%, 2.6%]	7
Improvements ✅ (primary)	-2.8%	[-2.8%, -2.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.9%	[-2.8%, 1.1%]	2

Cycles

Results (primary -2.4%, secondary 28.5%)

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)	28.5%	[28.5%, 28.5%]	1
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.4%	[-2.4%, -2.4%]	1

Binary size

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

Bootstrap: 491.114s -> 492.029s (0.19%)
Artifact size: 394.23 MiB -> 394.80 MiB (0.14%)

[rustbot]

changes to the core type system

cc @lcnr

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred to the core trait solver

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

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

[rust-timer]

This pull request is already queued and waiting for a try build to finish.

[rust-bors]

⌛ Trying commit cf2f7aa with merge 92f830b…

To cancel the try build, run the command @bors try cancel.

Workflow: https://github.com/rust-lang/rust/actions/runs/25374278223

[jdonszelmann]

actually, there's no need, perf will run on the big CI @bors try cancel
was curious how this PR would do with the new benchmarks in the perf suite

[rust-bors]

Try build cancelled. Cancelled workflows:

• https://github.com/rust-lang/rust/actions/runs/25374278223

[rustbot]

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.

[jdonszelmann]

@bors p=1 rollup=never (has been quite bitrotty, also perf)

[jdonszelmann]

@bors r=lcnr

[rust-bors]

📌 Commit 36b6eeb has been approved by lcnr

It is now in the queue for this repository.

[JonathanBrouwer]

@bors p=6
Scheduling this before the next rollup