compute_trait_goal structural equality fast path

[lcnr]

Fixes the hang in rayon and rust-lang/trait-system-refactor-initiative#210.

This changes means we now have a far stronger reliance on structural identity making rust-lang/trait-system-refactor-initiative#127 a significantly larger problem. However, I've come to believe that fast paths based on structural equality are just too desirable. Solves that issue by uniquifying root goals only during HIR typeck. Fixes github.com/rust-lang/trait-system-refactor-initiative/issues/27

Fixes #139409.

r? @compiler-errors

[rustbot]

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

[lcnr]

@ors2 try @rust-timer queue

[lcnr]

TODO: this incorrect marks param_env candidates as global :<

[lcnr]

TODO: I don't fully get why this one compiles now 🤔

[lcnr]

we've got the proof tree

• T: Trait
  • via env: AliasRelate(T::Assoc, T) no solution
    • NormalizesTo(T::Assoc)
      • compute proven_via for T: Trait
        • via AliasRelate(T::Assoc, T) unproductive cycle
        • via impl -> T

we currently never try to actually normalize T::Assoc outside of applying the param env candidate. Doing this has the following proof tree

• NormalizesTo(T::Assoc)
  • compute proven_via for T: Trait
    • via AliasRelate(T::Assoc, T) err
      • NormalizesTo(T::Assoc) unproductive cycle no solution
    • via impl -> T
• cycle rerun (provisional result: normalizes-to T)
  • compute proven_via for T: Trait
    • via AliasRelate(T::Assoc, T) ok
      • NormalizesTo(T::Assoc) cycle provisional result T
  • alias is rigid
• cycle rerun (provisional result: normalizes-to T::Assoc)
  • compute proven_via for T: Trait
    • via AliasRelate(T::Assoc, T) err
      • NormalizesTo(T::Assoc) cycle provisional result T::Assoc
  • via impl -> T
• ...fail to reach fixpoint

This should start failing again with #140558 and changes it's behavior as this PR simply causes checking whether the <T as Trait>::Assoc: Trait to use the fast path instead of normalizing the self type

[lcnr]

@bors2 try

[rust-bors]

⌛ Trying commit 8c737ce with merge 2f05b1f…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 2f05b1f (2f05b1f742a5c897ad5434184c44474f4107be5e, parent: 67819923ac8ea353aaa775303f4c3aacbf41d010)

[rust-timer]

Finished benchmarking commit (2f05b1f): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-5.5%, -0.3%]	8
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -3.9%)

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%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.9%	[-11.4%, -3.1%]	3
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -2.2%, secondary -3.3%)

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)	1.7%	[1.7%, 1.7%]	1
Improvements ✅ (primary)	-2.2%	[-2.2%, -2.2%]	1
Improvements ✅ (secondary)	-4.3%	[-5.7%, -2.4%]	5
All ❌✅ (primary)	-2.2%	[-2.2%, -2.2%]	1

Binary size

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

Bootstrap: 465.321s -> 462.652s (-0.57%)
Artifact size: 374.50 MiB -> 374.44 MiB (-0.02%)