use a single large catch_unwind in lang_start

[RalfJung]

I originally planned to use abort_unwind but reading the comment in thread_cleanup it seems we are deliberately going for slightly nicer error messages here, so this preserves that. It still seems nice to not repeat catch_unwind so often.

[rustbot]

r? @ibraheemdev

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[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[joboet]

Sounds good.
@bors r+
r? joboet

[bors]

📌 Commit 471d830 has been approved by joboet

It is now in the queue for this repository.

[bors]

⌛ Testing commit 471d830 with merge e491cae...

[bors]

☀️ Test successful - checks-actions
Approved by: joboet
Pushing e491cae to master...

[rust-timer]

Finished benchmarking commit (e491cae): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.7%, -0.1%]	6
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 4.4%)

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)	4.4%	[4.4%, 4.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.4%	[4.4%, 4.4%]	1

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: 764.65s -> 764.175s (-0.06%)
Artifact size: 326.06 MiB -> 326.11 MiB (0.02%)