Skip Lazy for some metadata tables

[cjgillot]

Some metadata tables encode their entries indirectly, through the Lazy construct. This is useful when dealing with variable length encoding, but incurs the extra cost of one u32.

Meanwhile, some fields can be encoded in a single u8, or can use a short fixed-length encoding. This PR proposes to do so, and avoid the overhead.

[cjgillot]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 39fd6f674c492d209f83a490ebaf10cbf0b150a8 with merge 15d46b8154c4bad80167c6cbf595c14757a5d34d...

[bors]

💔 Test failed - checks-actions

[cjgillot]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit b4cf2cd with merge 20b8a895ef404521ba7fac00e8f75e13eb407af4...

[bors]

☀️ Try build successful - checks-actions
Build commit: 20b8a895ef404521ba7fac00e8f75e13eb407af4 (20b8a895ef404521ba7fac00e8f75e13eb407af4)

[rust-timer]

Queued 20b8a895ef404521ba7fac00e8f75e13eb407af4 with parent 32c2630, future comparison URL.

[rust-timer]

Finished benchmarking commit (20b8a895ef404521ba7fac00e8f75e13eb407af4): comparison url.

Summary:

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 🎉 relevant improvements found

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	0	0	0	9	0
mean2	N/A	N/A	N/A	-0.3%	N/A
max	N/A	N/A	N/A	-0.4%	N/A

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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-review -S-waiting-on-perf -perf-regression

Footnotes

1. number of relevant changes ↩

2. the arithmetic mean of the percent change ↩

[cjgillot]

Perf reports no change in instruction count, and a ~1.5 % decrease in max-rss.

r? rust-lang/compiler

[oli-obk]

@bors r+ rollup=never

[bors]

📌 Commit b4cf2cd has been approved by oli-obk

[bors]

⌛ Testing commit b4cf2cd with merge de56c29...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing de56c29 to master...

[rust-timer]

Finished benchmarking commit (de56c29): comparison url.

Summary:

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: mixed results

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	0	5	0	1	0
mean2	N/A	0.4%	N/A	-0.7%	N/A
max	N/A	0.5%	N/A	-0.7%	N/A

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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

Footnotes

1. number of relevant changes ↩

2. the arithmetic mean of the percent change ↩

[cjgillot]

The PR provides a consistent reduction in max-rss ~1.5-2%. The instruction count result is less than 1% and mixed.
@rustbot label: +perf-regression-triaged