Optimize io::Write::write_fmt for constant strings

[thaliaarchi]

When the formatting args to fmt::Write::write_fmt are a statically known string, it simplifies to only calling write_str without a runtime branch. Do the same in io::Write::write_fmt with write_all.

Also, match the convention of fmt::Write for the name of args.

[rustbot]

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[thaliaarchi]

This change is extracted from #137762 and does not use fmt::Arguments::estimated_capacity, unlike the rest of that PR, so is not affected by the heuristics which likely overallocate the capacity. I think this is likely beneficial on its own.

Can we do a perf run?

cc @workingjubilee

[Kobzol]

@bors try @rust-timer queue

[bors]

⌛ Trying commit a0c3dd4 with merge 8b7fc8c...

[bors]

☀️ Try build successful - checks-actions
Build commit: 8b7fc8c (8b7fc8cbf54ba3210a57b028a2cc040dba8e8150)

[rust-timer]

Finished benchmarking commit (8b7fc8c): comparison URL.

Overall result: no relevant changes - 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 benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary -2.0%, secondary 0.2%)

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)	5.5%	[5.5%, 5.5%]	1
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-5.8%	[-9.1%, -2.5%]	2
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	-2.0%	[-9.1%, 5.5%]	3

Cycles

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

Binary size

Results (primary 0.1%)

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%, 0.2%]	10
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-0.1%, 0.2%]	12

Bootstrap: 776.409s -> 774.964s (-0.19%)
Artifact size: 365.11 MiB -> 365.16 MiB (0.01%)

[thaliaarchi]

This is a runtime thing, so I'm not surprised we're not seeing any change in the compile time benchmarks. I think that means we're good.

[ibraheemdev]

The benchmarks measure the run time of the compiler. It seems unlikely to use io::Write with a constant string, but given that we already do this in fmt::Write, it seems reasonable. @bors r+ rollup

[bors]

📌 Commit a0c3dd4 has been approved by ibraheemdev

It is now in the queue for this repository.