Implement StableHasher::write_u128 via write_u64

[saethlin]

In #110367 (comment) the cachegrind diffs indicate that nearly all the regression is from this:

22,892,558  ???:<rustc_data_structures::sip128::SipHasher128>::slice_write_process_buffer
-9,502,262  ???:<rustc_data_structures::sip128::SipHasher128>::short_write_process_buffer::<8>

Which happens because the diff for that perf run swaps a Hash::hash of a u64 to a u128. But slice_write_process_buffer is a #[cold] function, and is for handling hashes of arbitrary-length byte arrays.

Using the much more optimizer-friendly u64 path twice to hash a u128 provides a nice perf boost in some benchmarks.

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit ad8d304 with merge 29bb036a6ff39a9cb5841c4f2affd349246adbd9...

[bors]

☀️ Try build successful - checks-actions
Build commit: 29bb036a6ff39a9cb5841c4f2affd349246adbd9 (29bb036a6ff39a9cb5841c4f2affd349246adbd9)

[bors]

☀️ Try build successful - checks-actions
Build commit: 29bb036a6ff39a9cb5841c4f2affd349246adbd9 (29bb036a6ff39a9cb5841c4f2affd349246adbd9)

[rust-timer]

Finished benchmarking commit (29bb036a6ff39a9cb5841c4f2affd349246adbd9): 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)	-0.3%	[-0.4%, -0.3%]	3
Improvements ✅ (secondary)	-0.6%	[-0.9%, -0.5%]	14
All ❌✅ (primary)	-0.3%	[-0.4%, -0.3%]	3

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

This benchmark run did not return any relevant results for this metric.

[oli-obk]

r? @oli-obk @bors r+

[bors]

📌 Commit ad8d304 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit ad8d304 with merge 3860251...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 3860251 to master...

[rust-timer]

Finished benchmarking commit (3860251): 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)	-0.7%	[-2.8%, -0.2%]	13
Improvements ✅ (secondary)	-1.9%	[-7.5%, -0.2%]	24
All ❌✅ (primary)	-0.7%	[-2.8%, -0.2%]	13

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)	1.5%	[1.3%, 1.7%]	3
Regressions ❌ (secondary)	3.2%	[3.1%, 3.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.5%	[1.3%, 1.7%]	3

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)	-	-	0
Improvements ✅ (secondary)	-3.1%	[-3.8%, -2.0%]	4
All ❌✅ (primary)	-	-	0

[lqd]

Note for weekly triage: cranelift-codegen and keccak are currently very noisy unfortunately, e.g.