[early rough draft] GCI: Don't evaluate free const items with impossible predicates

[fmease]

No description provided.

[fmease]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 74ec3ea with merge 4151b9a…

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[fmease]

This one might be dicey since we don't check requires_own_monomorization. impossible_predicates is likely wrong without it. Example by Boxy: <T> [T]: Sized.

[BoxyUwU]

We should consider moving all of these call-site checks into ctfe itself, e.g. eval_to_const_value_raw_provider. This wont affect const patterns which go through _for_typeck versions of the CTFE entry points.

I also then think that the impossible predicates check in that place should ICE on predicates containing non region params as that shouldn't be reachable (and if it is, then we're evaluating generic constants in places we might not want to be).

[BoxyUwU]

This being one such place where we evaluate generic stuff where we probably oughtn't

[rust-bors]

☀️ Try build successful (CI)
Build commit: 4151b9a (4151b9aaad261468f4260336981f34de2f05df15)

[rust-timer]

Finished benchmarking commit (4151b9a): comparison URL.

Overall result: no relevant changes - 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.

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@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary -5.1%, secondary -2.1%)

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)	3.5%	[3.5%, 3.5%]	1
Improvements ✅ (primary)	-5.1%	[-9.4%, -3.0%]	6
Improvements ✅ (secondary)	-2.3%	[-4.3%, -1.1%]	21
All ❌✅ (primary)	-5.1%	[-9.4%, -3.0%]	6

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: 753.145s -> 753.291s (0.02%)
Artifact size: 372.18 MiB -> 372.22 MiB (0.01%)