Tweak inlining attributes for slice indexing

[saethlin]

Doing some experiments in response to this unexpected regression: #120863 (comment)

I expect the opt changes to be addressed by something like reviving #91222. The debug changes are what I'm interested in.

Codegen tests will probably fail from time to time in this PR, I will fix them up later but also I don't trust the opt-level-z one: #119878 (comment)

r? @ghost

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 574235c with merge 4c5b313...

[bors]

☀️ Try build successful - checks-actions
Build commit: 4c5b313 (4c5b313c74be7d45f00d6ad93783d8229294dbc1)

[rust-timer]

Finished benchmarking commit (4c5b313): comparison URL.

Overall result: ✅ improvements - 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)	-	-	0
Improvements ✅ (primary)	-1.0%	[-1.3%, -0.5%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.0%	[-1.3%, -0.5%]	4

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)	4.1%	[2.3%, 5.8%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-5.2%, -0.2%]	7
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.0%	[-5.2%, 5.8%]	9

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)	-1.5%	[-1.9%, -1.0%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.5%	[-1.9%, -1.0%]	3

Binary size

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)	0.1%	[0.0%, 0.1%]	10
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	4
Improvements ✅ (primary)	-0.2%	[-0.6%, -0.0%]	37
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-0.6%, 0.1%]	47

Bootstrap: 639.883s -> 640.879s (0.16%)
Artifact size: 308.63 MiB -> 308.65 MiB (0.00%)

[saethlin]

I think the right thing to do here is change the semantics of inline(always). I think the codegen test mentioned in the PR description should have demanded that we add these long ago.