Experiment: Replace ShardedHashMap method insert with debug-checked insert_unique

[zetanumbers]

Currently every use of ShardedHashMap::insert checks that it won't evict an old value due to unique key. I haven't found any issue related to that faulty condition, so I thought of replacing it with ShardedHashMap::insert_unique which doesn't check for this condition unless debug_assertions are enabled. This might improve the performance.

r? @petrochenkov

[lqd]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: db613ff (db613ff78761d3debfa74a42bb3a2f4d649e3a2b, parent: e22c616e4e87914135c1db261a03e0437255335e)

[rust-timer]

Finished benchmarking commit (db613ff): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.4%	[-0.7%, -0.2%]	10
Improvements ✅ (secondary)	-0.5%	[-0.7%, -0.1%]	23
All ❌✅ (primary)	-0.4%	[-0.7%, -0.2%]	10

Max RSS (memory usage)

This perf run didn't have relevant results for this metric.

Cycles

Results (secondary -2.5%)

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)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	20
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	19
All ❌✅ (primary)	-0.1%	[-0.1%, -0.0%]	20

Bootstrap: 507.073s -> 490.745s (-3.22%)
Artifact size: 394.31 MiB -> 394.24 MiB (-0.02%)