Trim unused CoreCLR native components from dotnet-linker-tests build

[sbomer]

The Runtime_Release jobs in the dotnet-linker-tests pipeline build the clr subset. That expands to clr.native, which performs a full CoreCLR native build — including several components the trimming and NativeAOT tests never use:

• alljits — six cross-target alt-JITs (clrjit_universal_arm64_x64, clrjit_win_x86_x64, clrjit_universal_wasm_x64, etc.)
• spmi — SuperPMI and its three shims

Together these are 703 of 2837 ninja targets (~25%) of the CoreCLR native build.

This narrows the subset list to just the components the tests actually need. src/coreclr/components.cmake shows the runtime component already depends on jit, iltools, debug and hosts, so clr.runtime covers everything required to run the tests, and clr.tools + clr.nativeaotlibs + clr.nativeaotruntime cover ILCompiler and the NativeAOT test apps. Only ILCompiler.ReadyToRun.Tests needs alljits, and it builds them itself on demand.

Two further subsets pulled in by clr are also dropped:

• clr.packages only produces the ILAsm/ILDAsm/TestHost/Sdk.IL nupkgs, referenced solely by eng/Publishing.props for official-build publishing. (Packing them takes ~2.5s, so this is a cleanliness change, not a perf one.)
• clr.crossarchtools is redundant here — _BuildCrossComponents is already set whenever ClrRuntimeBuildSubsets is non-empty for CoreCLR, and the cross-tool build is gated on _BuildAnyCrossArch, which is false for native windows-x64/linux-x64. Verified no cross-arch build directory is produced either way.

Measurements

CI runs the native build at ninja -j 4, so measurements were taken locally at the same parallelism:

	ninja targets	native build @ -j4
Before (clr)	2837	4m03s
After	2134	3m05s
Delta	−703 (−24.8%)	−58s (−24%)

Applied to the current CI native phases (15.6m on windows-x64, 11.0m on linux-x64), this should take roughly 3.5–4 min off the critical-path windows-x64 job, which currently runs ~62m within a ~75m build. linux-x64 saves ~2.6m but stays off the critical path. The browser-wasm job is unaffected (it builds mono, not clr).

The −24% is likely conservative for Windows, which drops a larger share of targets (780/2646 = 29.5%) since Linux keeps clrjit_unix_x64_x64 as part of the base jit component.

Validation

From a clean tree with the narrowed subsets:

• Build succeeds
• Trimming tests: 88 tests pass
• NativeAOT test apps: 57 tests pass
• Artifacts verified: only the host libclrjit.so remains, superpmi is gone, and libcoreclr.so, ilc, crossgen2, ilasm/ildasm, DAC/mscordbi and the aotsdk are all still present

Note

This content was created with assistance from AI.

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[Copilot]

Pull request overview

Updates the runtime-linker-tests Azure Pipelines definition to build a narrower set of CoreCLR subsets for the Runtime_Release jobs, aiming to avoid building unused native components during trimming and NativeAOT test runs.

Changes:

• Replaces -s clr+... with an explicit subset list centered on clr.runtime plus NativeAOT/tooling subsets.
• Adds inline pipeline comments documenting why alljits and spmi are intentionally excluded.

Show a summary per file

File	Description
eng/pipelines/runtime-linker-tests.yml	Switches the CoreCLR build from clr to an explicit subset list intended to avoid building unused native components for linker/NativeAOT tests.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0 new