[EXPERIMENT DO NOT MERGE] remove span tracking during lowering

[jdonszelmann]

r? @ghost

Just a little experiment to see how much it gains us. All incremental tests pass, I've not found a place yet where it matters that we track them. It makes some sense, spans are relative to their parent anyway so it makes some sense that they're regenerated anyway if their parent changes. But I can't yet prove this. I am wondering how much perf it gains us.

[jdonszelmann]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: f592d8b (f592d8b65d4bd187ed675b06225568ccbe3a1a30, parent: 2a3a62d26e9e5badb806ac6a43bb307ff472b514)

[rust-timer]

Finished benchmarking commit (f592d8b): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-0.1%, -0.1%]	3

Max RSS (memory usage)

Results (primary -2.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.5%	[-2.5%, -2.5%]	1

Cycles

Results (secondary -6.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.1%	[-6.1%, -6.1%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 472.42s -> 475.345s (0.62%)
Artifact size: 389.33 MiB -> 389.30 MiB (-0.01%)

[jdonszelmann]

Well that ain't worth it

[jdonszelmann]

Sad 🤷