[rustc_data_structures][base_n][perf] Remove unnecessary utf8 check.

[ttsugriy]

Since all output characters taken from BASE_64 are valid UTF8 chars there is no need to waste cycles on validation.

Even though it's obviously a perf win, I've also used a benchmark on M1 MacBook Air with following results:

Running benches/base_n_benchmark.rs (target/release/deps/base_n_benchmark-825fe5895b5c2693)
push_str/old            time:   [14.670 µs 14.852 µs 15.074 µs]
Found 11 outliers among 100 measurements (11.00%)
  4 (4.00%) high mild
  7 (7.00%) high severe
push_str/new            time:   [12.573 µs 12.674 µs 12.801 µs]
Found 11 outliers among 100 measurements (11.00%)
  7 (7.00%) high mild
  4 (4.00%) high severe

[rustbot]

r? @davidtwco

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[Noratrieb]

let's see whether this has a perf impact in the big picture
@bors try @rust-timer-queue

[bors]

⌛ Trying commit 64dfd10 with merge 54dae55966c4fd1e2fffedc9a1c6a16d6df6f073...

[klensy]

Some years ago i tried something similar #86214

[bors]

☀️ Try build successful - checks-actions
Build commit: 54dae55966c4fd1e2fffedc9a1c6a16d6df6f073 (54dae55966c4fd1e2fffedc9a1c6a16d6df6f073)

[Noratrieb]

it seems likely to me that the perf impact will be negligible (actually this code might be off by default and only used in v0 mangling) but even then, I'd expect it to not matter that much. That said, the safety invariant here is trivial to uphold as it always writes ASCII bytes so it's not that problematic.

[Noratrieb]

oops, wrong command
@rust-timer build 54dae55966c4fd1e2fffedc9a1c6a16d6df6f073

[rust-timer]

Finished benchmarking commit (54dae55966c4fd1e2fffedc9a1c6a16d6df6f073): 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)	-0.5%	[-0.8%, -0.3%]	2
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.3%]	3
All ❌✅ (primary)	-0.5%	[-0.8%, -0.3%]	2

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)	-	-	0
Regressions ❌ (secondary)	3.7%	[3.7%, 3.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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)	-1.7%	[-1.7%, -1.7%]	1
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	-1.7%	[-1.7%, -1.7%]	1

Binary size

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

Bootstrap: missing data

[davidtwco]

@bors r+

[bors]

📌 Commit 64dfd10 has been approved by davidtwco

It is now in the queue for this repository.

[bors]

⌛ Testing commit 64dfd10 with merge 617821a...

[bors]

☀️ Test successful - checks-actions
Approved by: davidtwco
Pushing 617821a to master...

[rust-timer]

Finished benchmarking commit (617821a): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-3.5%, -0.9%]	6
All ❌✅ (primary)	-	-	0

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)	-2.5%	[-2.5%, -2.5%]	3
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 634.018s -> 633.541s (-0.08%)