Skip no-op drop glue

[Mark-Simulacrum]

Since #122662 this no longer gets used in vtables, so we're safe to fully
drop generating these empty functions. Those are eventually cleaned up
by LLVM, but it's wasteful to produce them in the first place.

This doesn't appear to be a significant win (and shows some slight regressions) but
seems like the right thing to do. At minimum it reduces noise in the LLVM IR we generate,
which seems like a good thing.

[Mark-Simulacrum]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit c839507 with merge d28feb0…

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

[rust-bors]

☀️ Try build successful (CI)
Build commit: d28feb0 (d28feb066e95d7ce212acfb87a21d02aa98b8928, parent: 9822e3dc15b5940626a186a57f877cf784b1bfb3)

[rust-timer]

Finished benchmarking commit (d28feb0): 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)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.2%]	5
Improvements ✅ (secondary)	-2.0%	[-2.9%, -0.6%]	5
All ❌✅ (primary)	-0.1%	[-0.4%, 1.0%]	6

Max RSS (memory usage)

Results (primary -1.5%, secondary 2.7%)

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

	mean	range	count
Regressions ❌ (primary)	1.9%	[1.6%, 2.1%]	3
Regressions ❌ (secondary)	2.7%	[2.1%, 4.0%]	3
Improvements ✅ (primary)	-3.5%	[-5.2%, -2.6%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.5%	[-5.2%, 2.1%]	8

Cycles

Results (primary 1.1%, secondary -0.8%)

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

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	6.1%	[6.1%, 6.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.3%, -2.2%]	4
All ❌✅ (primary)	1.1%	[1.1%, 1.1%]	1

Binary size

Results (primary -0.3%, 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)	0.3%	[0.1%, 1.0%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.8%, -0.0%]	44
Improvements ✅ (secondary)	-1.6%	[-5.0%, -0.0%]	17
All ❌✅ (primary)	-0.3%	[-0.8%, 1.0%]	48

Bootstrap: 757.645s -> 756.931s (-0.09%)
Artifact size: 372.28 MiB -> 372.23 MiB (-0.01%)

[Mark-Simulacrum]

It seems to me this test is mostly a duplicate of the unsizing test, so I'm skipping updating it with its own drop glue variant -- seems like that's covered there. Maybe worth deleting one of these entirely in a follow-up PR though.

[rustbot]

r? @fee1-dead

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They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rustbot]

Some changes occurred in tests/codegen/sanitizer

cc @rcvalle