Dogfood -Zno-embed-metadata in the standard library

[Kobzol]

This PR dogfoods the -Zno-embed-metadata flag in the standard library. This removes the .rmeta portion out of the libstd.so file, thus reducing its filesize on disk. Notably, this reduces the amount of MiB that we ship to people who download the standard library.

I think that the only way to find out what this breaks is to try to run full CI, and then try to land it on nightly :)

r? @ghost

[Kobzol]

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: 6edf4f5 (6edf4f50158d893f8aa51ea5a04ba02370776b95, parent: b1b26b834d85e84b46aa8f8f3ce210a1627aa85f)

[Kobzol]

@rust-timer build 6edf4f5

[rust-timer]

Finished benchmarking commit (6edf4f5): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.7%	[0.2%, 1.2%]	7
Regressions ❌ (secondary)	0.4%	[0.1%, 0.9%]	43
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.5%, -0.0%]	3
All ❌✅ (primary)	0.7%	[0.2%, 1.2%]	7

Max RSS (memory usage)

Results (primary -0.7%, secondary -0.8%)

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

	mean	range	count
Regressions ❌ (primary)	1.3%	[1.3%, 1.3%]	1
Regressions ❌ (secondary)	2.7%	[2.3%, 3.2%]	4
Improvements ✅ (primary)	-1.4%	[-2.3%, -0.5%]	3
Improvements ✅ (secondary)	-2.5%	[-5.2%, -0.8%]	8
All ❌✅ (primary)	-0.7%	[-2.3%, 1.3%]	4

Cycles

Results (primary 3.6%, secondary 3.7%)

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

	mean	range	count
Regressions ❌ (primary)	3.6%	[3.6%, 3.6%]	1
Regressions ❌ (secondary)	3.7%	[2.0%, 5.3%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.6%	[3.6%, 3.6%]	1

Binary size

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

Bootstrap: 464.328s -> 465.28s (0.21%)
Artifact size: 377.44 MiB -> 377.37 MiB (-0.02%)

[bors]

☔ The latest upstream changes (presumably #145366) made this pull request unmergeable. Please resolve the merge conflicts.

[Kobzol]

@bors try @rust-timer queue

[Kobzol]

@bors try @rust-timer queue

[Kobzol]

@bors try @rust-timer queue

[Kobzol]

r? @bjorn3

[bors]

☔ The latest upstream changes (presumably #149836) made this pull request unmergeable. Please resolve the merge conflicts.

[Kobzol]

@bors2 r+

(Just testing new bors)

[rust-bors]

📌 Commit b143030 has been approved by Kobzol

It is now in the queue for this repository.

[Kobzol]

@bors2 r-

[rust-bors]

Commit b143030 has been unapproved.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[Kobzol]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 0dfbe35 (0dfbe35c2f554bb94fb5ece5a7da73b275a5bc94, parent: 1b4325211c3228dd10eea12e9b3f749f87363d95)

[rust-timer]

Finished benchmarking commit (0dfbe35): comparison URL.

Overall result: ❌ regressions - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.8%	[0.2%, 1.2%]	7
Regressions ❌ (secondary)	0.3%	[0.1%, 0.9%]	52
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	1
All ❌✅ (primary)	0.8%	[0.2%, 1.2%]	7

Max RSS (memory usage)

Results (primary 0.3%, secondary -1.0%)

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

	mean	range	count
Regressions ❌ (primary)	1.6%	[1.6%, 1.6%]	1
Regressions ❌ (secondary)	1.2%	[0.7%, 1.9%]	6
Improvements ✅ (primary)	-1.0%	[-1.0%, -1.0%]	1
Improvements ✅ (secondary)	-3.5%	[-4.8%, -2.1%]	5
All ❌✅ (primary)	0.3%	[-1.0%, 1.6%]	2

Cycles

Results (secondary 0.6%)

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)	2.6%	[2.3%, 3.0%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-3.6%, -1.3%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 472.736s -> 473.671s (0.20%)
Artifact size: 390.80 MiB -> 382.61 MiB (-2.10%)

[Kobzol]

The performance regression exists only for the most trivial crates and benchmarks that are almost empty. I think that they are caused by rustc now scanning an additional .rmeta stdlib file with the metadata:

   85,803    <&std::path::PathBuf as core::hash::Hash>::hash::<rustc_hash::FxHasher>
   44,811    emap_try_acquire_edata_neighbor
  -27,503    extent_try_coalesce_impl
    9,281    <rustc_metadata::locator::CrateLocator>::find_library_crate
    8,461    free
   -7,779    <object::read::any::File>::parse
    7,582    <rustc_session::search_paths::SearchPath>::new
   -7,000    <object::read::elf::section::SectionTable<object::elf::FileHeader64<object::endian::Endianness>>>::symbols
    6,820    realloc
    6,604    malloc
   -6,440    <object::read::archive::ArchiveMember>::parse::<&[u8]>

The libstd.so size difference:

• Before (https://ci-artifacts.rust-lang.org/rustc-builds/1b4325211c3228dd10eea12e9b3f749f87363d95/rust-std-nightly-x86_64-unknown-linux-gnu.tar.xz): 32 MiB compressed, 167 MiB uncompressed
• After (https://ci-artifacts.rust-lang.org/rustc-builds/0dfbe35c2f554bb94fb5ece5a7da73b275a5bc94/rust-std-nightly-x86_64-unknown-linux-gnu.tar.xz): 30 MiB compressed, 159 MiB uncompressed

[Kobzol]

@rustbot ready