Offload bootstrap

[ZuseZ4]

The recommended way to build the offload project changed.
While already at it, testing how much overhead we get from building (or shipping) the two runtimes.

r? @Kobzol

[rustbot]

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

[ZuseZ4]

@bors2 try @rust-timer queue

(@Kobzol feel free to change if you want to see something else).

[rust-bors]

💔 Test for 7069335 failed: CI. Failed jobs:

• try - dist-x86_64-linux (web logs, extended logs)

[ZuseZ4]

@bors2 try @rust-timer queue

[rust-bors]

💔 Test for 31000c9 failed: CI. Failed jobs:

• try - dist-x86_64-linux (web logs, extended logs)

[ZuseZ4]

@bors2 try @rust-timer queue

[rust-bors]

💔 Test for de7bdfa failed: CI. Failed jobs:

• try - dist-x86_64-linux (web logs, extended logs)

[ZuseZ4]

@bors2 try @rust-timer queue

[ZuseZ4]

It seems like llvm_profile_generate wasn't part of the solution, so just to verify that PGO still succeeds without it:

@bors2 try @rust-timer queue

[ZuseZ4]

@Kobzol: This is ready for approval if you don't have any other concerns. I'd squash it before merge, just leaving it for now so you see what changed.
It works locally, so I'd like to keep it either way, even if we have to later temporarily disable it for nighlty.
I was therefore wondering, should I split the Dockerfile update into it's own PR, so we can only revert that (and keep this) if something goes wrong?

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8b3d163 (8b3d163a03686b03f5a5b772ed9c5da56de65dc8, parent: 3391c0133661be933c3ef24edf1867d71b9f206b)

[rust-timer]

Finished benchmarking commit (8b3d163): comparison URL.

Overall result: no relevant changes - 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

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

Max RSS (memory usage)

Results (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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.0%	[-1.0%, -1.0%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -2.1%, secondary -3.0%)

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)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-3.0%	[-5.4%, -2.1%]	5
All ❌✅ (primary)	-2.1%	[-2.1%, -2.1%]	1

Binary size

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

Bootstrap: 473.663s -> 472.194s (-0.31%)
Artifact size: 389.32 MiB -> 389.31 MiB (-0.00%)

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-2 failed! Check out the build log: (web) (plain enhanced) (plain)

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

fmt: checked 6591 files
tidy check
tidy [rustdoc_json (src)]: `rustdoc-json-types` modified, checking format version
tidy: Skipping binary file check, read-only filesystem
tidy [style (src)]: /checkout/src/bootstrap/src/core/build_steps/compile.rs:2267: tab character
tidy [style (src)]: /checkout/src/bootstrap/src/core/build_steps/compile.rs:2268: tab character
tidy [style (src)]: /checkout/src/bootstrap/src/core/build_steps/compile.rs:2270: tab character
tidy [style (src)]: FAIL
tidy: The following check failed: style (src)
Command `/checkout/obj/build/aarch64-unknown-linux-gnu/stage1-tools-bin/rust-tidy /checkout /checkout/obj/build/aarch64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 yarn` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1612:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1358:29

Command has failed. Rerun with -v to see more details.
Bootstrap failed while executing `--stage 2 test --skip tests --skip coverage-map --skip coverage-run --skip library --skip tidyselftest`
Build completed unsuccessfully in 0:00:58
  local time: Sat Dec 13 17:49:45 UTC 2025
  network time: Sat, 13 Dec 2025 17:49:45 GMT
##[error]Process completed with exit code 1.