Wild experiments

[mati865]

Looks like there is quite a lot of a publicity here, so I probably at least provide minimal info if somebody wants to try it out.

You can try it locally out by adding -Clinker=wild to RUSTFLAGS or with cargo +<toolchain_name> rustc -- -C linker=wild and verify whether it works by running readelf -p .comment target/debug/<binary/shared object name> | rg -i linker - it should say Wild ....
This experiment only covers x86_64-unknown-linux-gnu host for now.

[mati865]

One last thing to try.
@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 87248e1 (87248e14656411e3502b645bd0deff132c90db6c, parent: ddaf12390d3ffb7d5ba74491a48f3cd528e5d777)

[rust-timer]

Finished benchmarking commit (87248e1): 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)	-3.1%	[-8.2%, -0.3%]	29
Improvements ✅ (secondary)	-1.8%	[-8.1%, -0.1%]	72
All ❌✅ (primary)	-3.1%	[-8.2%, -0.3%]	29

Max RSS (memory usage)

Results (primary -8.1%)

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)	-8.1%	[-11.8%, -4.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-8.1%	[-11.8%, -4.3%]	2

Cycles

Results (primary 13.4%, secondary 10.7%)

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

	mean	range	count
Regressions ❌ (primary)	13.4%	[2.4%, 30.0%]	9
Regressions ❌ (secondary)	10.7%	[2.0%, 29.4%]	29
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	13.4%	[2.4%, 30.0%]	9

Binary size

Results (primary -1.2%, secondary -2.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.9%, 0.9%]	4
Regressions ❌ (secondary)	1.3%	[0.8%, 1.4%]	4
Improvements ✅ (primary)	-1.5%	[-3.3%, -0.4%]	27
Improvements ✅ (secondary)	-2.8%	[-4.9%, -0.0%]	49
All ❌✅ (primary)	-1.2%	[-3.3%, 0.9%]	31

Bootstrap: 473.077s -> 516.803s (9.24%)
Artifact size: 390.10 MiB -> 390.15 MiB (0.01%)

[mati865]

@bors try @rust-timer queue

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

tidy check
Checking tidy rustdoc_json...
No error code explanation was removed!
tidy: Skipping binary file check, read-only filesystem
##[error]tidy error: /checkout/compiler/rustc_target/src/spec/mod.rs:131: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
removing old virtual environment
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'venv'
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'virtualenv'
Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (25.2)
linting python files
---
linting javascript files and applying suggestions
Running eslint on rustdoc JS files
info: ES-Check: there were no ES version matching errors!  🎉
typechecking javascript files
some tidy checks failed
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/rust-tidy /checkout /checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 /node/bin/npm --extra-checks=py,cpp,js,spellcheck` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1657:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1281:29

Command has failed. Rerun with -v to see more details.
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Build completed unsuccessfully in 0:03:24
  local time: Mon Sep 15 10:01:48 UTC 2025
  network time: Mon, 15 Sep 2025 10:01:48 GMT
##[error]Process completed with exit code 1.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8d02507 (8d02507f77424e2db34b91eaac187b532c4f3244, parent: d1ed52b1f5b78bf66127b670af813b84d57aeedb)

[rust-timer]

Finished benchmarking commit (8d02507): 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)	-3.2%	[-8.9%, -0.4%]	29
Improvements ✅ (secondary)	-1.9%	[-7.6%, -0.1%]	71
All ❌✅ (primary)	-3.2%	[-8.9%, -0.4%]	29

Max RSS (memory usage)

Results (primary -5.7%)

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)	-5.7%	[-12.4%, -0.6%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-5.7%	[-12.4%, -0.6%]	3

Cycles

Results (primary 9.0%, secondary 10.3%)

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

	mean	range	count
Regressions ❌ (primary)	11.0%	[2.3%, 29.2%]	11
Regressions ❌ (secondary)	11.2%	[2.2%, 31.7%]	28
Improvements ✅ (primary)	-2.2%	[-2.2%, -2.2%]	2
Improvements ✅ (secondary)	-1.9%	[-2.3%, -1.4%]	2
All ❌✅ (primary)	9.0%	[-2.2%, 29.2%]	13

Binary size

Results (primary -1.1%, secondary -1.7%)

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

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.9%, 0.9%]	4
Regressions ❌ (secondary)	1.3%	[0.8%, 1.4%]	4
Improvements ✅ (primary)	-1.4%	[-3.3%, -0.4%]	31
Improvements ✅ (secondary)	-1.8%	[-4.9%, -0.0%]	85
All ❌✅ (primary)	-1.1%	[-3.3%, 0.9%]	35

Bootstrap: 473.872s -> 517.604s (9.23%)
Artifact size: 390.16 MiB -> 390.17 MiB (0.00%)

[mati865]

Summary of Wild compared to LLD:

• without forking (Unix syscall) the linker: https://perf.rust-lang.org/compare.html?start=637b50be01093962ac6f4432d6881ab41d6d90b4&end=3a5439fb15a90156a0db2aab1a7daa0be6cdf1c7&stat=wall-time
• with fork: https://perf.rust-lang.org/compare.html?start=02c7b1a7ac1d739663878030510508372e46f254&end=cee02659a5c76c78bcae425edbfe4c97d767f214&stat=wall-time
• with fork, ThinLTO and @lqd's PR to skip excluded sections: https://perf.rust-lang.org/compare.html?start=ddaf12390d3ffb7d5ba74491a48f3cd528e5d777&end=87248e14656411e3502b645bd0deff132c90db6c&stat=wall-time
• with fork, ThinLTO, @lqd's PR to skip excluded sections, and capping Wild's threads to 8: https://perf.rust-lang.org/compare.html?start=d1ed52b1f5b78bf66127b670af813b84d57aeedb&end=8d02507f77424e2db34b91eaac187b532c4f3244&stat=wall-time&nonRelevant=true

Keep in mind those are wall-times which are prone to be noisy, so focus on the general tendencies, rather than specific cases.

[hkBst]

I was puzzled by bootstrap taking longer, but that is because it now also includes the time to build wild, right?

[mati865]

Yes, I made it a part of rustc to make the benchmarking simple. In the proper setup, it'd be an optional component that can be enabled or disabled.