GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants #136429

fmease · 2025-02-02T10:44:18Z

1st commit: Partially addresses #136204 by turning const eval errors from post to pre-mono for free lifetime-generic constants.
Re. 2nd commit: Oof, yeah, I missed that in the initial impl!

This doesn't fully address #136204 because I still haven't figured out how & where to properly & best suppress const eval of free constants whose predicates don't hold at the def site. The motivating example is #![feature(trivial_bounds)] const _UNUSED: () = () where String: Copy; which can also be found over at the tracking issue #113521.

r? compiler-errors or reassign

fmease · 2025-02-02T10:45:18Z

compiler/rustc_hir_analysis/src/lib.rs

-                let typing_env = ty::TypingEnv::fully_monomorphized();
-                tcx.ensure().eval_to_const_value_raw(typing_env.as_query_input(cid));
+            DefKind::Const if !tcx.generics_of(item_def_id).requires_monomorphization(tcx) => {
+                tcx.ensure().const_eval_poly(item_def_id.into())


This temporarily 'reverts' the perf optimization from #121387. I have to see what to do about this.

IINM const_eval_poly would be the 'most correct' option since we do want to construct the Instance with identity substs (contrary to empty ones) and likely do want use the ParamEnv of the free constant lol (tho I've yet to find an example where the latter makes a difference it practice)

fmease · 2025-02-02T10:45:58Z

@bors try @rust-timer queue

bors · 2025-02-02T10:47:10Z

⌛ Trying commit 5a8ee9b with merge ea1cdda...

GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants 1st commit: Partially addresses rust-lang#136204 by turning const eval errors from post to pre-mono for free lifetime-generic constants. Re. 2nd commit: Oof, that's embarrassing! How could I miss that in the initial impl? This doesn't fully address rust-lang#136204 because I still haven't figured out how & where to properly & best suppress const eval of free constants whose predicates don't hold at the def site. The motivating example is `#![feature(trivial_bounds)] const _UNUSED: () = () where String: Copy;` which can also be found over at the tracking issue rust-lang#113521. r? compiler-errors or reassign

tests/ui/generic-const-items/def-site-predicates-wf.rs

bors · 2025-02-02T12:36:23Z

☀️ Try build successful - checks-actions
Build commit: ea1cdda (ea1cdda3b51a1290675800f2196813f4bfc693bd)

rust-timer · 2025-02-02T13:54:03Z

Finished benchmarking commit (ea1cdda): comparison URL.

Overall result: ❌ regressions - please read the text below

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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.4%, 1.1%]	8
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.9%	[0.4%, 1.1%]	8

Max RSS (memory usage)

Results (primary 1.5%, secondary -2.0%)

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)	1.5%	[1.0%, 2.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	1.5%	[1.0%, 2.0%]	2

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: 777.275s -> 776.801s (-0.06%)
Artifact size: 328.69 MiB -> 328.73 MiB (0.01%)

compiler/rustc_hir_analysis/src/check/wfcheck.rs

rustbot · 2025-02-03T04:27:00Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @rust-lang/wg-const-eval

Co-authored-by: Michael Goulet <michael@errs.io>

Probably won't make a difference because erase_regions no-ops on region-erased things anyway.

fmease · 2025-02-03T04:37:11Z

@bors try @rust-timer queue

GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants 1st commit: Partially addresses rust-lang#136204 by turning const eval errors from post to pre-mono for free lifetime-generic constants. Re. 2nd commit: Oof, yeah, I missed that in the initial impl! This doesn't fully address rust-lang#136204 because I still haven't figured out how & where to properly & best suppress const eval of free constants whose predicates don't hold at the def site. The motivating example is `#![feature(trivial_bounds)] const _UNUSED: () = () where String: Copy;` which can also be found over at the tracking issue rust-lang#113521. r? compiler-errors or reassign

bors · 2025-02-03T04:38:22Z

⌛ Trying commit 9f2fdff with merge 6f11489...

bors · 2025-02-03T06:28:05Z

☀️ Try build successful - checks-actions
Build commit: 6f11489 (6f11489377389dbe08c91408f1c8f953933c18cd)

RalfJung · 2025-02-03T07:57:05Z

turning const eval errors from post to pre-mono for free lifetime-generic constants.

This should be listed as an item in the tracking issue to make sure it is discussed during stabilization.

fmease · 2025-02-03T08:01:30Z

I'll go you one better and mention it in the upcoming RFC.

rust-timer · 2025-02-03T08:23:16Z

Finished benchmarking commit (6f11489): comparison URL.

Overall result: ❌ regressions - please read the text below

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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.2%, 1.1%]	6
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.2%, 1.1%]	6

Max RSS (memory usage)

Results (primary -0.3%)

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)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.0%	[-3.0%, -3.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-3.0%, 2.4%]	2

Cycles

Results (primary 2.0%)

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)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Binary size

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

Bootstrap: 778.369s -> 778.266s (-0.01%)
Artifact size: 328.65 MiB -> 328.70 MiB (0.01%)

fmease added the F-generic_const_items `#![feature(generic_const_items)]` label Feb 2, 2025

rustbot assigned compiler-errors Feb 2, 2025

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 Feb 2, 2025

fmease commented Feb 2, 2025

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tests/ui/generic-const-items/def-site-predicates-wf.rs Outdated Show resolved Hide resolved

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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 Feb 2, 2025

compiler-errors reviewed Feb 2, 2025

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compiler/rustc_hir_analysis/src/check/wfcheck.rs Outdated Show resolved Hide resolved

fmease force-pushed the gci-fix-def-site-checks branch from 5a8ee9b to 1dc3d6e Compare February 3, 2025 04:26

fmease force-pushed the gci-fix-def-site-checks branch from 1dc3d6e to 9c2b71a Compare February 3, 2025 04:27

fmease marked this pull request as draft February 3, 2025 04:28

fmease and others added 3 commits February 3, 2025 05:35

Always evaluate free lifetime-generic constants

57a68fb

Co-authored-by: Michael Goulet <michael@errs.io>

GCI: Check where-clauses for well-formedness at the def site

f0e361f

TyCtxtEnsure::const_eval_poly: Don't try to erase regions twice

9f2fdff

Probably won't make a difference because erase_regions no-ops on region-erased things anyway.

fmease force-pushed the gci-fix-def-site-checks branch from 9c2b71a to 9f2fdff Compare February 3, 2025 04:36

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 3, 2025

fmease added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 4, 2025

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GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants #136429

GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants #136429

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rust-timer commented Feb 3, 2025

GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants #136429

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GCI: At their def site, actually wfcheck the where-clause & always eval free lifetime-generic constants #136429

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Overall result: ❌ regressions - please read the text below

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Overall result: ❌ regressions - please read the text below

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