hygiene: Avoid recursion in syntax context decoding

[petrochenkov]

#139241 has two components

• Avoiding recursion during syntax context decoding
• Encoding/decoding only the non-redundant data, and recalculating the redundant data again during decoding

Both of these parts may influence compilation times, possibly in opposite directions.
So this PR contains only the first part to evaluate its effect in isolation.

[rustbot]

r? @BoxyUwU

rustbot has assigned @BoxyUwU.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[petrochenkov]

@bors try @rust-timer queue

[bors]

⌛ Trying commit fef3cf0 with merge 16553d2...

[BoxyUwU]

r? compiler

[bors]

☀️ Try build successful - checks-actions
Build commit: 16553d2 (16553d2192c698a649c1b626e2f82b499c9c5490)

[rust-timer]

Finished benchmarking commit (16553d2): 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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-0.4%	[-0.8%, -0.2%]	12
Improvements ✅ (secondary)	-0.6%	[-0.8%, -0.1%]	18
All ❌✅ (primary)	-0.4%	[-0.8%, -0.2%]	12

Max RSS (memory usage)

Results (primary -4.0%, secondary 0.0%)

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)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	2.7%	[1.3%, 4.8%]	3
Improvements ✅ (primary)	-9.1%	[-9.1%, -9.1%]	1
Improvements ✅ (secondary)	-4.0%	[-5.8%, -2.1%]	2
All ❌✅ (primary)	-4.0%	[-9.1%, 1.1%]	2

Cycles

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

Binary size

Results (primary -0.1%, 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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.0%]	77
Improvements ✅ (secondary)	-0.2%	[-0.6%, -0.0%]	34
All ❌✅ (primary)	-0.1%	[-0.4%, -0.0%]	77

Bootstrap: 776.833s -> 776.783s (-0.01%)
Artifact size: 365.93 MiB -> 365.92 MiB (-0.00%)

[petrochenkov]

Nice, this part is a pure win.
@rustbot ready

[wesleywiser]

@bors r+

[bors]

📌 Commit fef3cf0 has been approved by wesleywiser

It is now in the queue for this repository.

[bors]

⌛ Testing commit fef3cf0 with merge da83217...

[bors]

☀️ Test successful - checks-actions
Approved by: wesleywiser
Pushing da83217 to master...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 1e008dd (parent) -> da83217 (this PR)

Test differences

Show 8 test diffs

Additionally, 8 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Job duration changes

1. x86_64-apple-2: 5253.8s -> 6834.3s (30.1%)
2. dist-armv7-linux: 5214.9s -> 5397.9s (3.5%)
3. dist-i686-msvc: 6746.1s -> 6980.2s (3.5%)
4. test-various: 4198.9s -> 4323.5s (3.0%)
5. dist-various-1: 4358.8s -> 4473.4s (2.6%)
6. dist-powerpc64-linux: 5336.6s -> 5472.8s (2.6%)
7. armhf-gnu: 4430.4s -> 4542.0s (2.5%)
8. dist-apple-various: 6249.1s -> 6394.3s (2.3%)
9. dist-arm-linux: 5380.3s -> 5503.2s (2.3%)
10. x86_64-msvc-ext3: 7351.5s -> 7513.9s (2.2%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (da83217): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-0.7%, -0.4%]	3
Improvements ✅ (secondary)	-0.6%	[-0.7%, -0.3%]	14
All ❌✅ (primary)	-0.5%	[-0.7%, -0.4%]	3

Max RSS (memory usage)

Results (secondary 1.4%)

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)	3.6%	[2.6%, 5.4%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.3%, -1.7%]	2
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 3.3%, secondary -6.5%)

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)	3.3%	[3.3%, 3.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.5%	[-8.8%, -2.1%]	3
All ❌✅ (primary)	3.3%	[3.3%, 3.3%]	1

Binary size

Results (primary -0.1%, 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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.0%]	78
Improvements ✅ (secondary)	-0.2%	[-0.6%, -0.0%]	34
All ❌✅ (primary)	-0.1%	[-0.4%, -0.0%]	78

Bootstrap: 777.007s -> 778.037s (0.13%)
Artifact size: 365.98 MiB -> 365.98 MiB (-0.00%)