never patterns: lower never patterns to Unreachable in MIR

[Nadrieril]

This lowers a ! pattern to "goto Unreachable". Ideally I'd like to read from the place to make it clear that the UB is coming from an invalid value, but that's tricky so I'm leaving it for later.

r? @compiler-errors how do you feel about a lil bit of MIR lowering

[compiler-errors]

hmmmm maybe r? @matthewjasper instead?

happy to review it if matthewjasper is unavailable tho

[Nadrieril]

I deleted this because it felt like an entirely artificial construct and I couldn't find a sensible name to keep it under. What surprises me is that it took something so complicated to break the feature back when it was explicitly not lowering to MIR correctly. It's probably not minimal

[matthewjasper]

@bors r+

[bors]

📌 Commit 57e8aeb has been approved by matthewjasper

It is now in the queue for this repository.

[bors]

⌛ Testing commit 57e8aeb with merge 0f40f14...

[bors]

☀️ Test successful - checks-actions
Approved by: matthewjasper
Pushing 0f40f14 to master...

[rust-timer]

Finished benchmarking commit (0f40f14): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -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
Regressions ❌ (secondary)	4.1%	[4.1%, 4.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-2.6%	[-2.6%, -2.6%]	1
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

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)	-	-	0
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-3.8%	[-3.8%, -3.8%]	1
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Binary size

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

Bootstrap: 676.002s -> 676.385s (0.06%)
Artifact size: 315.77 MiB -> 315.93 MiB (0.05%)