Let codegen decide when to mem::swap with immediates

[scottmcm]

Making libcore decide this is silly; the backend has so much better information about when it's a good idea.

Thus this PR introduces a new typed_swap intrinsic with a fallback body, and replaces that fallback implementation when swapping immediates or scalar pairs.

r? oli-obk

Replaces #111744, and means we'll never need more libs PRs like #111803 or #107140

[rustbot]

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

The Miri subtree was changed

cc @rust-lang/miri

[scottmcm]

@bors try @rust-timer queue

[bors]

⌛ Trying commit e583c57 with merge 3f68c63...

[bors]

☀️ Try build successful - checks-actions
Build commit: 3f68c63 (3f68c63f114f4d57b01ae74bc549e4b68f955eee)

[RalfJung]

Should it be called typed_swap_nonoverlapping?

[scottmcm]

I went back and forth multiple times on this. typed_swap_nonoverlapping sounds to me like ptr::swap_nonoverlapping, just typed. So that would make this typed_swap_nonoverlapping_one or something, and now that's just seeming really long.

So since it's internal, I think I'm inclined to leave it as-is for now unless someone feels particularly strongly about it.

[RalfJung]

I feel like the "nonoverlapping" distinction is way more fundamental than the "one" distinction. And since it is internal, consistency with ptr::swap_nonoverlapping isn't very important IMO.

[bors]

💔 Test failed - checks-actions

[scottmcm]

@bors r=oli-obk

[bors]

📌 Commit 75d2e5b has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 75d2e5b with merge ea4d0e9...

[bors]

💥 Test timed out

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RalfJung]

@bors retry

[bors]

⌛ Testing commit 75d2e5b with merge d6eb0f5...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing d6eb0f5 to master...

[rust-timer]

Finished benchmarking commit (d6eb0f5): comparison URL.

Overall result: ✅ improvements - 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)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.4%	[-0.4%, -0.4%]	1

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)	4.3%	[0.1%, 6.8%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-5.3%	[-5.3%, -5.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.9%	[-5.3%, 6.8%]	4

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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%, 0.4%]	27
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-1.0%, -0.0%]	10
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-1.0%, 0.4%]	37

Bootstrap: 669.588s -> 671.198s (0.24%)
Artifact size: 315.05 MiB -> 314.95 MiB (-0.03%)