Fix `Deref` args when `#[const_trait]` is enabled #118386

compiler-errors · 2023-11-27T19:51:48Z

Fix Deref being a #[const_trait]. To fix this fully, we also need to pass the host param to method_autoderef_steps and make sure we use it correctly in Autoderef.

compiler-errors · 2023-11-27T19:51:52Z

@rustbot author

bors · 2023-11-28T11:21:58Z

☔ The latest upstream changes (presumably #118282) made this pull request unmergeable. Please resolve the merge conflicts.

compiler-errors · 2023-12-15T17:15:21Z

This code is still broken for two reasons:

method_autoderef_steps doesn't know anything about the constness of the function, so it fails to select a Deref impl cause of ambiguity
Projections have a host parameter but we don't currently know what to do with them...

compiler-errors · 2023-12-18T20:19:32Z

This is ready :>

We just need to pass the host param to Autoderef and canonicalize it in method_autoderef_steps.

@bors try @rust-timer queue

bors · 2023-12-18T20:20:42Z

⌛ Trying commit 38e0402 with merge 4a90a2c...

Fix `Deref` args when `#[const_trait]` is enabled r? `@fee1-dead` This is still pretty broken, but putting this PR up so I don't lose the code in some `git stash` somewhere...

bors · 2023-12-18T21:47:29Z

☀️ Try build successful - checks-actions
Build commit: 4a90a2c (4a90a2c83dbb51ae7aa0f7efa5b3aba7cd165e4f)

rust-timer · 2023-12-18T23:58:54Z

Finished benchmarking commit (4a90a2c): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.1%, 0.7%]	38
Regressions ❌ (secondary)	0.5%	[0.2%, 0.8%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.1%, 0.7%]	38

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.8%	[0.8%, 0.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-2.7%, -2.7%]	1
All ❌✅ (primary)	-	-	0

Cycles

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

Binary size

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

Bootstrap: 673.958s -> 673.623s (-0.05%)
Artifact size: 312.41 MiB -> 312.44 MiB (0.01%)

compiler-errors · 2023-12-19T00:06:56Z

I feel like we just need to accept this perf regression 😅, since it's likely not possible to avoid needing to pass in the host param in method_autoderef_steps, and we're simply doing more work here. Happy to discuss this if anyone disagrees, though.

fee1-dead

sorry about the lack of response here, r=me after the two tiny nits

compiler/rustc_middle/src/ty/util.rs

tests/ui/rfcs/rfc-2632-const-trait-impl/effects/const_closure-const_trait_impl-ice-113381.rs

compiler-errors · 2024-01-08T15:16:12Z

I'm curious about perf...

@bors try @rust-timer queue

bors · 2024-01-08T15:17:22Z

⌛ Trying commit a453884 with merge 34aeaa2...

Fix `Deref` args when `#[const_trait]` is enabled Fix `Deref` being a `#[const_trait]`. To fix this fully, we also need to pass the host param to `method_autoderef_steps` and make sure we use it correctly in `Autoderef`.

bors · 2024-01-08T16:43:57Z

☀️ Try build successful - checks-actions
Build commit: 34aeaa2 (34aeaa28971ceecb8ae34abcf0c3d6ab41e0a673)

rust-timer · 2024-01-09T00:19:16Z

Finished benchmarking commit (34aeaa2): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.2%, 0.7%]	40
Regressions ❌ (secondary)	0.4%	[0.2%, 0.8%]	11
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.2%, 0.7%]	40

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.9%, 0.9%]	1
Regressions ❌ (secondary)	10.5%	[10.5%, 10.5%]	1
Improvements ✅ (primary)	-0.8%	[-1.1%, -0.5%]	2
Improvements ✅ (secondary)	-1.9%	[-2.5%, -1.3%]	3
All ❌✅ (primary)	-0.2%	[-1.1%, 0.9%]	3

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-0.6%	[-0.8%, -0.5%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.6%	[-0.8%, -0.5%]	2

Binary size

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

Bootstrap: 667.831s -> 668.134s (0.05%)
Artifact size: 308.39 MiB -> 308.55 MiB (0.05%)

fee1-dead · 2024-01-09T11:23:56Z

I think there may be potential optimizations related to caching behavior with the host generic params. Currently the trait system would probably cache non-const trait bounds and const trait bounds separately. If we find a way to mark which host args come from the original obligation carried forward, then we'd only need to select traits once (considering that concrete impls like impl const always implements both non-const and const, giving us a happy path).

I'm not entirely sure why we'd have this many regressions, though. expected_host_effect_param_for_body is only different if we are in a const fn, where there shouldn't be any deref (though we'd still have to check when typechecking method calls?) We might try to fix the regressions on stable code by checking the effects feature somewhere, and just passing in tcx.consts.true_ if we don't have effects enabled.

fee1-dead · 2024-01-09T12:23:33Z

Well, hmm, it looks like expected_host_effect_param_for_body already forces the host the param to be true. Why would this have a regression then?

compiler-errors · 2024-01-09T15:28:51Z

I think it may just be due to additional caching. I will test a few things, but otherwise I feel like we should absorb the perf hit since it seems inevitable.

fee1-dead · 2024-01-14T10:27:02Z

feel free to r=me after you have done the testing

compiler-errors · 2024-03-19T16:57:15Z

This is gonna have to be reworked after @fee1-dead adjusts the const trait desugaring, I think. Or otherwise, this can be revived later.

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Nov 27, 2023

rustbot assigned fee1-dead Nov 27, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 27, 2023

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compiler-errors mentioned this pull request Nov 28, 2023

Fix PartialEq args when #[const_trait] is enabled #118379

Merged

fee1-dead mentioned this pull request Dec 6, 2023

Tracking Issue for removing impl const and ~const in the standard library #110395

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Dec 18, 2023

compiler-errors removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 19, 2023

fee1-dead approved these changes Dec 26, 2023

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compiler-errors added 2 commits January 8, 2024 01:12

Fix Deref args when #[const_trait] is enabled

31f5cfd

Pass host param in method_autoderef_steps

a453884

rust-cloud-vms bot force-pushed the const-deref branch from 38e0402 to a453884 Compare January 8, 2024 01:23

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Fix `Deref` args when `#[const_trait]` is enabled #118386

Fix `Deref` args when `#[const_trait]` is enabled #118386

compiler-errors commented Nov 27, 2023 •

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Fix Deref args when #[const_trait] is enabled #118386

Fix Deref args when #[const_trait] is enabled #118386

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Overall result: ❌ regressions - ACTION NEEDED

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Overall result: ❌ regressions - ACTION NEEDED

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Fix `Deref` args when `#[const_trait]` is enabled #118386

Fix `Deref` args when `#[const_trait]` is enabled #118386

compiler-errors commented Nov 27, 2023 •

edited