Make function bodies with &! arguments unreachable

[saethlin]

Implementation of rust-lang/unsafe-code-guidelines#413 (comment)

r? @ghost

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit dedc3b3 with merge 0f4641ea16e650c77a03aa649330702722a5f66f...

[bors]

☀️ Try build successful - checks-actions
Build commit: 0f4641ea16e650c77a03aa649330702722a5f66f (0f4641ea16e650c77a03aa649330702722a5f66f)

[rust-timer]

Finished benchmarking commit (0f4641ea16e650c77a03aa649330702722a5f66f): comparison URL.

Overall result: ❌ regressions - no action needed

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.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -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)	1.9%	[0.3%, 5.1%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

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: 647.37s -> 646.714s (-0.10%)

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 9e5c162 with merge b7380c57d311609c0fd4f128fbe8adbbe0f96a24...

[bors]

☀️ Try build successful - checks-actions
Build commit: b7380c57d311609c0fd4f128fbe8adbbe0f96a24 (b7380c57d311609c0fd4f128fbe8adbbe0f96a24)

[rust-timer]

Finished benchmarking commit (b7380c57d311609c0fd4f128fbe8adbbe0f96a24): comparison URL.

Overall result: no relevant changes - no action needed

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.

@bors rollup=never
@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

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

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: 649.476s -> 647.446s (-0.31%)

[bjorn3]

cg_clif has this code which directly emits an unreachable instruction instead for uninhabited arguments: https://github.com/bjorn3/rustc_codegen_cranelift/blob/c07d1e2f88cb3b1a0604ae8f18b478c1aeb7a7fa/src/base.rs#L252-L261 In any case would you mind adding the peel_refs() call here too if this experiment is a success?