Detect unwind-free functions in MIR

[Mark-Simulacrum]

This adds analysis as part of inlining that will mark calls to functions with Unwind::Unreachable even if inlining is not possible, so long as their MIR indicates that they cannot unwind.

This would ideally persist into the codegen fn attrs, but that will take more work.

My guess is this implementation is not going to work in practice (too much overhead, not enough value?) but wanted to see what perf looked like.

[Mark-Simulacrum]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 05dc174 with merge 209ede6…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 209ede6 (209ede66b6181c8fa07f95666d9f6fe887e054b2, parent: 11ad40bb839ca16f74784b4ab72596ad85587298)

[rust-timer]

Finished benchmarking commit (209ede6): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	1.5%	[1.5%, 1.5%]	1
Improvements ✅ (primary)	-0.4%	[-0.9%, -0.3%]	12
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-0.3%	[-0.9%, 1.5%]	13

Max RSS (memory usage)

Results (primary -2.9%)

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)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-2.9%, -2.9%]	1

Cycles

Results (secondary -1.6%)

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)	1.3%	[1.3%, 1.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.0%, -2.2%]	3
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.1%, secondary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.1%, 0.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.0%]	42
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.0%]	57
All ❌✅ (primary)	-0.1%	[-0.3%, 0.1%]	43

Bootstrap: 694.764s -> 695.159s (0.06%)
Artifact size: 371.73 MiB -> 371.76 MiB (0.01%)