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Merged
merged 2 commits into from
Sep 23, 2025
Merged

Disable optimization to work around a compiler bug #807

merged 2 commits into from
Sep 23, 2025

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Steelskin
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This disables optimization on one function to work around a Swift compiler bug in the LLVM 21 rebranch.

Bug: swiftlang/llvm-project#11377

@Steelskin
Disable optimization to work around a compiler bug
8aef288 
This disables optimization on one function to work around a Swift
compiler bug in the LLVM 21 rebranch.

Bug: swiftlang/llvm-project#11377
@Steelskin
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@swift-ci please smoke test

owenv
owenv requested changes Sep 18, 2025
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Completely disabling LLVM optimizations here is probably going to have a very large impact on build perf. I think we need to take a closer look at the root cause before considering this workaround

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@owenv we are investigating the LLVM side of the issue. PEI is at fault here, and changing that is going to take some time. This is to unblock the work for the rebranch.

CC: @bnbarham @AnthonyLatsis

@bnbarham bnbarham mentioned this pull request Sep 18, 2025
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bnbarham commented Sep 18, 2025 •
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I've started a build in swiftlang/swift#71188 to see how far we get. If this is the only issue then we still have time to keep investigating. Worst case we might be able to split things up and only apply @_optimize(none) in a much narrower case? Though having said that, this function actually isn't doing all that much work is it 🤔 (it's all mostly in the called function)?

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owenv commented Sep 18, 2025

Could we restrict the attr to only target Windows? The bug seems to imply this only affects the windows prologue/epilogue emission?

@Steelskin
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Could we restrict the attr to only target Windows? The bug seems to imply this only affects the windows prologue/epilogue emission?

I'll see about limiting it to Windows/arm64, since it is the only affected platform AFAIK.

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#if os(Windows)
@_optimize(none)
#endif

Should do the trick.

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owenv commented Sep 18, 2025

ok, I'm ok with accepting this as a temporary change if we take @AnthonyLatsis 's suggestion

@Steelskin Steelskin requested a review from owenv September 18, 2025 19:12
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#if os(Windows)
@_optimize(none)
#endif

Should do the trick.

Thanks, done!

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@swift-ci please smoke test

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owenv commented Sep 18, 2025

@swift-ci test

(we don't have smoke test jobs in this repo bc they don't build the whole stack)

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There appears to be another problematic function in SwiftPM: https://ci-external.swift.org/job/swift-PR-build-toolchain-windows-arm64/42/console

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@swift-ci please test linux platform

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@swift-ci please test macos platform

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It looks like there is still one unrelated failure here but I can't re-run the job.

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FYI, I got the full Windows arm64 toolchain building locally in conjunction with swiftlang/swift-package-manager#9178

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owenv commented Sep 23, 2025

This is ok to merge, the failing job isn't fully brought up yet

@owenv owenv merged commit b14cb57 into swiftlang:main Sep 23, 2025
47 of 48 checks passed
@Steelskin Steelskin deleted the fabrice/workaround-disable-opt branch September 24, 2025 14:28
Steelskin added a commit to Steelskin/swift-swift-build that referenced this pull request Oct 7, 2025
@Steelskin
Revert Disable optimization to work around a compiler bug (swiftlang#807
59ecd28 
)

The compiler bug has been fixed so the workaround is no longer
necessary.

Bug: swiftlang/llvm-project#11377
@Steelskin Steelskin mentioned this pull request Oct 7, 2025
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compnerd pushed a commit that referenced this pull request Oct 7, 2025
@Steelskin @compnerd
Revert Disable optimization to work around a compiler bug (#807)
821fb53 
The compiler bug has been fixed so the workaround is no longer
necessary.

Bug: swiftlang/llvm-project#11377
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@neonichu neonichu neonichu approved these changes

@jakepetroules jakepetroules jakepetroules approved these changes

@owenv owenv owenv approved these changes

@aciidgh aciidgh Awaiting requested review from aciidgh aciidgh is a code owner

@mirza-garibovic mirza-garibovic Awaiting requested review from mirza-garibovic

@mhrawdon mhrawdon Awaiting requested review from mhrawdon mhrawdon is a code owner

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@Steelskin @compnerd @bnbarham @owenv @AnthonyLatsis @neonichu @jakepetroules