Development Snapshot failing at Windows * Developer Tools > Build swift-subprocess

[sundresh]

As of build #2918, "Windows * Developer Tools > Build swift-subprocess" has been failing. However, that doesn't mean that the problem was introduced between that build and the previous one, because through build #2917, the earlier "Build swift-docc" step was failing, so "Build swift-subprocess" had not been attempted for a while.

[sundresh]

The last good build of Development Snapshot was #2900. After that, in #2901, is when "Build swift-docc" started failing. So all we know right now is "Build swift-subprocess" started failing some time after build #2901 and before or at build #2918. The swiftlang/swift git SHAs for these are:

• build #2900: e33029b0055e9548f91adbb217a534d530e8295b
• build #2918: 966874a68e1aba9023e41e693433c500c88e6329
  The diff between these revisions is large. Maybe we can move swift-subprocess earlier in the build and then bisect to find the first failing build.

[sundresh]

A debug build using artifacts from build #2909 succeeds: https://github.com/thebrowsercompany/swift-build/actions/runs/21461980484/job/61816305547

Trying with artifacts from build #2914 next.

[sundresh]

Succeeded with artifacts from build #2914. Trying artifacts from build #2917.

[sundresh]

Success with compiler from build #2917: https://github.com/thebrowsercompany/swift-build/actions/runs/21462709173/job/61818460180
Failure with compiler from build #2918: https://github.com/thebrowsercompany/swift-build/actions/runs/21463396468/job/61820437614

All of the inputs are the same for those two runs except for the swiftlang/swift version, but that's not related, because they were taking the head of main at their build time just now, and not using it to build a compiler in these jobs.

Differences between swiftlang/swift revisions from builds #2917 and #2918: swiftlang/swift@12baaed...966874a

[sundresh]

Re-ran with -sil-verify-all: https://github.com/thebrowsercompany/swift-build/actions/runs/21464546963/job/61823811519

[sundresh]

The error message says the problem is in DCE. Maybe this commit which modifies ownership-related code in DCE? swiftlang/swift@a2a2374

[sundresh]

Reverting that merge commit still resulted in a broken build: https://github.com/thebrowsercompany/swift-build/actions/runs/21465825551
I'm trying building both at that merge commit and the merge commit after it to see if we can narrow it down to the commit after it, swiftlang/swift@0f3ddfb which also touches the relevant code.

[sundresh]

Building swift-subprocess also crashes for swiftlang/swift@a2a2374 - https://github.com/thebrowsercompany/swift-build/actions/runs/21468568568/job/61844717050

So:

• Revert this change --> swift-subprocess build crashes
• Build at this revision --> swift-subprocess build crashes
• Revision before this --> swift-subprocess build build succeeded with compiler previously built, but maybe something else changed in swift-build that would make it crash too? Except builds #2917 and #2918 both use the same revision of swift-build.
• Alternatively, maybe it's possible that multiple changes on the same day cause swift-subprocess builds to crash... in the same way?

[sundresh]

Actually, it looks like I didn't configure swift_revision correctly in the above runs. Retrying.

[mhegazy]

I am guessing it is one of the commits on swiftlang/swift#86545. i would just ping @jckarter for help with some details about the issue