Embed length of offset/position into Span tag byte

[Mark-Simulacrum]

This cuts the average bytes/relative span from 3.5 to 3.2 on libcore, ultimately saving ~400kb of data.

[rustbot]

r? @cjgillot

(rustbot has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 6367cf9 with merge 086d9ee...

[bors]

☀️ Try build successful - checks-actions
Build commit: 086d9ee (086d9ee99c9735fec5463094d495e65b0713e815)

[rust-timer]

Finished benchmarking commit (086d9ee): 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

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)	3.2%	[3.2%, 3.2%]	2
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-2.4%	[-2.4%, -2.4%]	1

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-1.4%, -0.0%]	92
Improvements ✅ (secondary)	-0.5%	[-1.1%, -0.1%]	43
All ❌✅ (primary)	-0.2%	[-1.4%, -0.0%]	92

Bootstrap: 669.562s -> 669.878s (0.05%)
Artifact size: 311.76 MiB -> 311.73 MiB (-0.01%)

[Mark-Simulacrum]

Rebased.

[cjgillot]

@bors r+

[bors]

📌 Commit 51dfe49 has been approved by cjgillot

It is now in the queue for this repository.

[bors]

⌛ Testing commit 51dfe49 with merge 8039906...

[bors]

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing 8039906 to master...

[rust-timer]

Finished benchmarking commit (8039906): comparison URL.

Overall result: ❌ regressions - 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)	1.3%	[1.3%, 1.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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.

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-1.4%, -0.0%]	94
Improvements ✅ (secondary)	-0.4%	[-1.2%, -0.0%]	40
All ❌✅ (primary)	-0.2%	[-1.4%, -0.0%]	94

Bootstrap: 646.106s -> 647.585s (0.23%)
Artifact size: 175.08 MiB -> 175.07 MiB (-0.00%)