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

[fmease]

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 const _UNUSED: () = () where for<'_delay> String: Copy; which can also be found over at the tracking issue #113521.

r? compiler-errors or reassign

[fmease]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 5a8ee9b with merge ea1cdda...

[bors]

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

[rust-timer]

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%)

[rustbot]

Some changes occurred to the CTFE / Miri interpreter

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

[fmease]

@bors try @rust-timer queue

[bors]

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

[bors]

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

[RalfJung]

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]

I've reverted the revert of the perf optimization from #121387 (meaning: we won't use const_eval_poly and we'll continue to pass empty substs instead of identity substs since that didn't seem to affect things negatively (I've left a FIXME ofc)), so marking
@bors rollup-
@rustbot label -perf-regression

With @BoxyUwU currently reworking&fixing wfchecking for type-system consts (and consts in general?) (see #137972, #140549, #140553) and with impossible predicates on const items leading to MIR Unreachables being the hot topic for other people, too, I'd like to postpone that part of issue #136204 and keep the scope of this PR limited / as is.

I don't want to interfere with Boxy's work which might even fix this and if not I'd at least have more time to gain intel on how to best fix it (I remember from February that there was some preexisting issues, like ImpossiblePredicates not considering non-global preds for example).

WDYT?

[fmease]

Actually let's perf run as a sanity check cuz I might've modified hot paths here and we're doing a bit more work.

@bors try @rust-timer queue

[bors]

⌛ Trying commit dabc874 with merge 3f34812...

[bors]

☀️ Try build successful - checks-actions
Build commit: 3f34812 (3f348129e6da6289f0ba3825919c2124c4cc6a89)

[rust-timer]

Finished benchmarking commit (3f34812): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.8%	[-2.8%, -2.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.2%	[-2.8%, 0.5%]	2

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)	1.4%	[0.5%, 3.0%]	6
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-1.9%, -0.4%]	35
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-1.9%, 3.0%]	41

Cycles

Results (primary -0.1%)

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)	0.5%	[0.4%, 0.7%]	8
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.0%	[-2.6%, -0.4%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-2.6%, 0.7%]	13

Binary size

Results (primary -1.1%)

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
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Bootstrap: 769.081s -> 770.42s (0.17%)
Artifact size: 365.55 MiB -> 365.42 MiB (-0.04%)