Inline fold operations for Chain and Map, for performance

[joshtriplett]

These show up in hot paths; let's see if this helps.

[rustbot]

r? @Darksonn

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

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: libs
• libs expanded to 12 candidates
• Random selection from Darksonn, JohnTitor, Mark-Simulacrum, clarfonthey

[joshtriplett]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: ddc0f5f (ddc0f5fe3d05348f68f2f635684aec7bf6ce6a48)
Base parent: 260f1ac (260f1acad9d7f70b5b56a636a9dc5a7f76150417)

[rust-timer]

Finished benchmarking commit (ddc0f5f): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@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%	[0.6%, 1.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.8%	[-13.3%, -0.2%]	15
Improvements ✅ (secondary)	-0.5%	[-3.2%, -0.1%]	36
All ❌✅ (primary)	-1.5%	[-13.3%, 1.5%]	17

Max RSS (memory usage)

Results (primary 1.2%)

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

	mean	range	count
Regressions ❌ (primary)	1.2%	[1.2%, 1.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.2%	[1.2%, 1.2%]	1

Cycles

Results (primary -5.7%, secondary 1.9%)

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)	4.4%	[1.6%, 6.8%]	9
Improvements ✅ (primary)	-5.7%	[-14.6%, -1.5%]	5
Improvements ✅ (secondary)	-9.5%	[-15.0%, -3.9%]	2
All ❌✅ (primary)	-5.7%	[-14.6%, -1.5%]	5

Binary size

Results (primary -0.9%, secondary -0.6%)

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

	mean	range	count
Regressions ❌ (primary)	3.4%	[3.4%, 3.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.0%	[-2.2%, -0.5%]	30
Improvements ✅ (secondary)	-0.6%	[-1.1%, -0.5%]	8
All ❌✅ (primary)	-0.9%	[-2.2%, 3.4%]	31

Bootstrap: 490.682s -> 490.616s (-0.01%)
Artifact size: 408.64 MiB -> 408.64 MiB (-0.00%)

[Darksonn]

Rerolling due to conference travel.

@rustbot reroll

[joshtriplett]

Based on the performance data, this seems to provide some pretty sizable wins.

[joshtriplett]

Closing in favor of #163845 which includes these and several more.