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alias-relate: add fast reject optimization #124852

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lcnr wants to merge 1 commit into rust-lang:master from lcnr:search-graph-uwu

+170 −4

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lcnr commented May 7, 2024 •

edited

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may be necessary to compile rayon rust-lang/trait-system-refactor-initiative#109

I don't like this PR too much and ideally we'd find a more principled way to avoid the exponential blowup(s) in rayon. Keeping this open for now but don't intend to merge this until we're more certain that it is required.

r? @compiler-errors

rustbot assigned compiler-errors

rustbot added S-waiting-on-review T-compiler WG-trait-system-refactor labels

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rustbot commented May 7, 2024

Some changes occurred to the core trait solver

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

Contributor Author

lcnr commented May 7, 2024

this unfortunately does not fix the hang in rayon. closing while we're trying other approaches

lcnr closed this

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compiler/rustc_trait_selection/src/solve/alias_relate.rs Outdated Show resolved Hide resolved

Contributor Author

lcnr commented May 12, 2024

if there's (): Trait<Assoc = TAIT> and TAIT is then defined to a placeholder, we can inject it into the env this way, even if it should error later. not yetsure whether and how we should handle this

rust-cloud-vms bot force-pushed the search-graph-uwu branch from 5908e13 to 97b546f Compare

May 13, 2024 14:11

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bors commented May 20, 2024

☔ The latest upstream changes (presumably #125324) made this pull request unmergeable. Please resolve the merge conflicts.

rust-cloud-vms bot force-pushed the search-graph-uwu branch from 97b546f to ea50666 Compare

May 21, 2024 20:09

compiler-errors reviewed

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compiler/rustc_trait_selection/src/solve/alias_relate.rs Outdated Show resolved Hide resolved

rust-cloud-vms bot force-pushed the search-graph-uwu branch from ea50666 to ac9bcd8 Compare

May 24, 2024 19:27

compiler-errors reviewed

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compiler/rustc_trait_selection/src/solve/alias_relate.rs Outdated

+                          return false;
+                      }
+                      let mut referenced_placeholders =

Member

compiler-errors May 25, 2024

Why IgnoreAliases::Yes?

Member

compiler-errors May 25, 2024

Feels like this fast reject could be quickly side-stepped w/ something like Mirror<!A> alias-relate Mirror<!B>

Member

compiler-errors May 25, 2024

Update: It occurred to me last night while I was sleeping that we ignore aliases here b/c e.g. Alias<!A> could normalize to sth not mentioning !A.

compiler/rustc_trait_selection/src/solve/alias_relate.rs Outdated

+                      let mut referenced_placeholders =
+                          self.collect_placeholders_in_term(rigid_term, IgnoreAliases::Yes);
+                      for clause in param_env.caller_bounds() {

Member

compiler-errors May 25, 2024

Would be nice to explain in detail what this is searching for. Specifically, we disqualify any of our rigid term's placeholders if they show up in projection goals, since that may assist in normalizing.

e.g. if we have

rigid = W<!A>
alias = Alias<!B>
param-env = [Alias<!B> normalizes-to W<!A>, ...]

then we exclude !A from our rigid placeholder list, right?

I think this may also be worth mentioning that this doesn't really care about how the placeholders show up in the term of the projection predicate, since this is really just a quick heuristic.

compiler/rustc_trait_selection/src/solve/alias_relate.rs Outdated

+                          }
+                      }
+                      if referenced_placeholders.is_empty() {

Member

compiler-errors May 25, 2024

Probably a somewhat redundant note, but maybe just say "empty set is a subset of everything, so no need to compute placeholders of alias"

compiler/rustc_trait_selection/src/solve/alias_relate.rs Outdated

+                      }
+                      let alias_placeholders = self.collect_placeholders_in_term(alias, IgnoreAliases::No);
+                      // If the rigid term references a placeholder not mentioned by the alias,

Member

compiler-errors May 25, 2024

Suggested change

      
                    // If the rigid term references a placeholder not mentioned by the alias,
          
                    // If the rigid term references a placeholder not mentioned by the alias, and isn't potentially reachable by a projection-predicate,

or something, to explain the way that the projection predicate search above influences this search

Member

compiler-errors commented May 25, 2024

My only outstanding question was answered by myself. I think the only tweaks I want are more thorough comments bc this code is subtle.

r=me afterwards

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compiler-errors commented Jun 4, 2024

@rustbot author

rustbot added S-waiting-on-author and removed S-waiting-on-review labels

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bors commented Jun 18, 2024

☔ The latest upstream changes (presumably #126614) made this pull request unmergeable. Please resolve the merge conflicts.

Member

JohnCSimon commented Sep 3, 2024

@lcnr
ping from triage - can you post your status on this PR? This PR has not received an update in a few months.

alex-semenyuk added S-waiting-on-author and removed S-waiting-on-author labels

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rayon hangs rust-lang/trait-system-refactor-initiative#109

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lcnr force-pushed the search-graph-uwu branch from 3b6ae40 to 17f3c98 Compare

February 25, 2025 10:45

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[DO NOT MERGE] bootstrap with -Znext-solver=globally #133502

Draft


          add alias-relate fast path optimization

8e51d74

lcnr force-pushed the search-graph-uwu branch from 17f3c98 to 8e51d74 Compare

April 9, 2025 19:38

bors added a commit to rust-lang-ci/rust that referenced this pull request


          Auto merge of rust-lang#133502 - lcnr:rust4, r=<try>

9970c3f

[DO NOT MERGE] bootstrap with `-Znext-solver=globally`

A revival of rust-lang#124812.

Current status:

~~`./x.py b --stage 2` passes 🎉~~

`try` builds succeed 🎉 🎉 🎉

[first perf run](rust-lang#133502 (comment)) 👻

### in-flight changes

- rust-lang#124852, unsure whether I actually want to land this PR for now
- rust-lang#139587
- https://github.com/lcnr/rust/tree/opaque-type-method-call

r? `@ghost`

bors added a commit to rust-lang-ci/rust that referenced this pull request


          Auto merge of rust-lang#133502 - lcnr:rust4, r=<try>

d81a6ae

[DO NOT MERGE] bootstrap with `-Znext-solver=globally`

A revival of rust-lang#124812.

Current status:

~~`./x.py b --stage 2` passes 🎉~~

`try` builds succeed 🎉 🎉 🎉

[first perf run](rust-lang#133502 (comment)) 👻

### in-flight changes

- rust-lang#124852, unsure whether I actually want to land this PR for now
- rust-lang#139587
- https://github.com/lcnr/rust/tree/opaque-type-method-call

r? `@ghost`

bors added a commit to rust-lang-ci/rust that referenced this pull request


          Auto merge of rust-lang#133502 - lcnr:rust4, r=<try>

14717a9

[DO NOT MERGE] bootstrap with `-Znext-solver=globally`

A revival of rust-lang#124812.

Current status:

~~`./x.py b --stage 2` passes 🎉~~

`try` builds succeed 🎉 🎉 🎉

[first perf run](rust-lang#133502 (comment)) 👻

### in-flight changes

- rust-lang#124852, unsure whether I actually want to land this PR for now
- rust-lang#139587
- https://github.com/lcnr/rust/tree/opaque-type-method-call

r? `@ghost`

bors added a commit to rust-lang-ci/rust that referenced this pull request


          Auto merge of rust-lang#133502 - lcnr:rust4, r=<try>

fa8e241

[DO NOT MERGE] bootstrap with `-Znext-solver=globally`

A revival of rust-lang#124812.

Current status:

~~`./x.py b --stage 2` passes 🎉~~

`try` builds succeed 🎉 🎉 🎉

[first perf run](rust-lang#133502 (comment)) 👻

### in-flight changes

- rust-lang#124852, unsure whether I actually want to land this PR for now
- rust-lang#139587
- https://github.com/lcnr/rust/tree/opaque-type-method-call
- rust-lang#138845
- https://gist.github.com/lcnr/86f3e56c3b25a7892d8dbfa28c84e1a8

r? `@ghost`

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