Get rid of USIZE_MARKER in formatting infrastructure

[joboet]

An alternative to #123780.

The USIZE_MARKER function used to differentiate between placeholder and count arguments is never called anyway, so we can just replace the function-pointer-comparison hack with an enum and an unreachable_unchecked, hopefully without causing a regression.

CC @RalfJung

[rustbot]

r? @Mark-Simulacrum

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[joboet]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 21c5ff8 with merge 90063dc...

[bors]

☀️ Try build successful - checks-actions
Build commit: 90063dc (90063dcdcca809560c3a21bf15363378d40ebb0d)

[bors]

☀️ Try build successful - checks-actions
Build commit: 90063dc (90063dcdcca809560c3a21bf15363378d40ebb0d)

[rust-timer]

Finished benchmarking commit (90063dc): comparison URL.

Overall result: ❌✅ regressions and improvements - 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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@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)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.4%	[-0.6%, -0.3%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-0.6%, 0.4%]	5

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)	4.8%	[4.5%, 5.1%]	2
Regressions ❌ (secondary)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	2
Improvements ✅ (secondary)	-4.3%	[-4.3%, -4.3%]	1
All ❌✅ (primary)	1.3%	[-2.3%, 5.1%]	4

Cycles

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

Binary size

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)	0.1%	[0.0%, 1.4%]	50
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	15
Improvements ✅ (primary)	-0.0%	[-0.1%, -0.0%]	8
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	34
All ❌✅ (primary)	0.1%	[-0.1%, 1.4%]	58

Bootstrap: 677.211s -> 675.448s (-0.26%)
Artifact size: 315.97 MiB -> 315.93 MiB (-0.01%)

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 0f52cd0 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

⌛ Testing commit 0f52cd0 with merge 7ab5eb8...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 7ab5eb8 to master...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 7ab5eb8 to master...

[rust-timer]

Finished benchmarking commit (7ab5eb8): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.6%	[0.4%, 0.9%]	2
Regressions ❌ (secondary)	1.5%	[1.5%, 1.5%]	1
Improvements ✅ (primary)	-0.4%	[-0.6%, -0.3%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-0.6%, 0.9%]	7

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)	2.7%	[0.8%, 5.1%]	5
Regressions ❌ (secondary)	3.0%	[1.0%, 4.5%]	9
Improvements ✅ (primary)	-5.1%	[-6.2%, -3.7%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-6.2%, 5.1%]	8

Cycles

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

Binary size

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)	0.1%	[0.0%, 1.3%]	49
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	13
Improvements ✅ (primary)	-0.1%	[-0.5%, -0.0%]	11
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	34
All ❌✅ (primary)	0.1%	[-0.5%, 1.3%]	60

Bootstrap: 676.211s -> 677.553s (0.20%)
Artifact size: 316.06 MiB -> 315.98 MiB (-0.03%)

[Kobzol]

More improvements than regressions.

@rustbot label: +perf-regression-triaged