Asyncdisplaykit: [Swift] Whole-module optimization may crash the Swift compiler with some apps?

[CodeEagle]

This block of code cause: Segmentation fault: 11

    import Foundation
    import AsyncDisplayKit

    //MARK:- ASLayoutable
    public extension ASLayoutable {

        func spec() -> ASLayoutSpec {
            return ASStaticLayoutSpec(children: [self])
        }

        func test() {
            let layout = ASLayoutSpec()
            let staticLayuot = layout.spec()
        }
    }

info

0  swift                    0x000000010618bfbb llvm::sys::PrintStackTrace(__sFILE*) + 43
1  swift                    0x000000010618c6fb SignalHandler(int) + 379
2  libsystem_platform.dylib 0x00007fff98e98eaa _sigtramp + 26
3  libsystem_platform.dylib 0x00007fee641294f0 _sigtramp + 3408463456
4  swift                    0x000000010494e31a swift::Substitution::subst(swift::ModuleDecl*, llvm::ArrayRef<swift::Substitution>, llvm::DenseMap<swift::TypeBase*, swift::Type, llvm::DenseMapInfo<swift::TypeBase*>, llvm::detail::DenseMapPair<swift::TypeBase*, swift::Type> >&, llvm::DenseMap<swift::ArchetypeType*, llvm::ArrayRef<swift::ProtocolConformance*>, llvm::DenseMapInfo<swift::ArchetypeType*>, llvm::detail::DenseMapPair<swift::ArchetypeType*, llvm::ArrayRef<swift::ProtocolConformance*> > >&) const + 1002
5  swift                    0x000000010494deff swift::Substitution::subst(swift::ModuleDecl*, swift::GenericParamList*, llvm::ArrayRef<swift::Substitution>) const + 1679
6  swift                    0x00000001046c638c swift::TypeSubstCloner<swift::GenericCloner>::remapSubstitution(swift::Substitution) + 60
7  swift                    0x00000001046c6265 swift::SILCloner<swift::GenericCloner>::getOpConformances(swift::ArchetypeType*, swift::CanType, llvm::ArrayRef<swift::ProtocolConformance*>) + 85
8  swift                    0x00000001046c616f swift::SILCloner<swift::GenericCloner>::getOpConformancesForExistential(swift::CanType, swift::CanType, llvm::ArrayRef<swift::ProtocolConformance*>) + 143
9  swift                    0x00000001046c0ecf swift::SILCloner<swift::GenericCloner>::visitInitExistentialRefInst(swift::InitExistentialRefInst*) + 79
10 swift                    0x00000001046b9beb swift::SILCloner<swift::GenericCloner>::visitSILBasicBlock(swift::SILBasicBlock*) + 59
11 swift                    0x00000001046b95ca swift::GenericCloner::populateCloned() + 522
12 swift                    0x00000001046c780c swift::GenericCloner::cloneFunction(swift::SILFunction*, llvm::DenseMap<swift::TypeBase*, swift::Type, llvm::DenseMapInfo<swift::TypeBase*>, llvm::detail::DenseMapPair<swift::TypeBase*, swift::Type> >&, llvm::DenseMap<swift::TypeBase*, swift::Type, llvm::DenseMapInfo<swift::TypeBase*>, llvm::detail::DenseMapPair<swift::TypeBase*, swift::Type> >&, llvm::StringRef, swift::ApplySite, std::__1::function<void (swift::SILInstruction*, swift::SILInstruction*)>) + 412
13 swift                    0x00000001046c74e1 swift::trySpecializeApplyOfGeneric(swift::ApplySite, swift::SILFunction*&, llvm::SmallVectorImpl<std::__1::pair<swift::ApplySite, swift::ApplySite> >&) + 1073
14 swift                    0x000000010451df03 (anonymous namespace)::SILPerformanceInliner::devirtualizeAndSpecializeApplies(llvm::SmallVectorImpl<swift::ApplySite>&, swift::CallGraphAnalysis*, swift::SILModuleTransform*, llvm::SmallVectorImpl<swift::SILFunction*>&) + 1539
15 swift                    0x000000010451b588 (anonymous namespace)::SILPerformanceInlinerPass::run() + 1544
16 swift                    0x00000001044e8d99 swift::SILPassManager::runOneIteration() + 1689
17 swift                    0x00000001044e72d2 swift::runSILOptimizationPasses(swift::SILModule&) + 402
18 swift                    0x000000010427cb16 performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&) + 11830
19 swift                    0x0000000104279ad3 frontend_main(llvm::ArrayRef<char const*>, char const*, void*) + 2691
20 swift                    0x0000000104276154 main + 2324
21 libdyld.dylib            0x00007fff9de295ad start + 1
22 libdyld.dylib            0x000000000000004a start + 1646095006

1. While running SILModuleTransform "Early Performance Inliner".

change to this code can solve the problem

public extension ASStaticLayoutable {

    var staticSpec: ASLayoutSpec {
        return ASStaticLayoutSpec(children: [self])
    }
}

But, why extension ASLayoutable will cause Segmentation fault: 11
ASLayoutable also comform to ASStaticLayoutable
@protocol ASLayoutable <ASStackLayoutable, ASStaticLayoutable, ASLayoutablePrivate>

[appleguy]

@CodeEagle that commit is huge - what was the change exactly? The code is written in Objective-C...

[CodeEagle]

@appleguy just ignore that commit ,the commit is a shortcut project , not for ASDK.....

and Segmentation fault: 11 will appear when

[appleguy]

@Adlai-Holler - have you tried the whole module optimization in your app? Give it a whirl and let me know if it crashes the compiler… I'm really not sure if this is a framework problem, or some kind of interaction with Extensions or other code that @CodeEagle has in their application.

[Adlai-Holler]

@appleguy Unfortunately this issue does reproduce even in a trivial project. Here's what I've observed:

This is the minimum I can do to get the compiler to crash:

// Compiler Crashes.
let bar = ASLayoutSpec().foo()

extension ASLayoutable {

    func foo() -> ASLayoutSpec {
        return ASStaticLayoutSpec(children: [self])
    }

}

Either one of these variations, and the compiler works great:

// Compiler Works.
// let bar = ASLayoutSpec().foo()

extension ASLayoutable {

    func foo() -> ASLayoutSpec {
        return ASStaticLayoutSpec(children: [self])
    }

}

// Compiler Works.
let bar = ASLayoutSpec().foo()

extension ASLayoutable {

    func foo() -> ASLayoutSpec {
        return ASStaticLayoutSpec(children: [])
    }

}

We definitely have a lot of protocol composition going on with ASLayoutable and its implementors but it all makes good sense. Considering the fact that removing self fixes the compiler crash, I think this is something out of my league in the Swift optimizer.

The issue is not resolved in Xcode 7.3 Beta 2, so I've submitted a bug to Apple https://openradar.appspot.com/radar?id=6191944728313856 as well as a reduced test case at https://github.com/Adlai-Holler/ASDKWMOTest

Unless someone can find something incorrect or janky in our Layoutable protocol hierarchy, we may have no path forward.

[aaronschubert0]

@appleguy @Adlai-Holler @CodeEagle
I would say this is more a programming error to be honest (granted there should be a better error message)

That is because you are basically trying to do this:
let foo = ASStaticLayoutSpec(children: [foo])
Which produces the error = "Variable used within its own initial value". The compiler is just getting confused at this point because the code passes the inline syntax validation (since it isn't fully aware of what your code is trying to accomplish)

So I would just use @Adlai-Holler second solution where you initialise the object with an empty array.
Maybe @CodeEagle you can share where you envisioned on using this, and we can code it in a different way?

[Adlai-Holler]

Hmm @aaronschubert0 are you sure that's the case? I believe the code is equivalent to:

let bar = ASStaticLayoutSpec(children: [ASLayoutSpec()])

[aaronschubert0]

@Adlai-Holler From this guide (https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Extensions.html) I would assume self to reference the initialised object rather than a new object of that type.

The extension on Int probably highlights this best (from the guide)

extension Int {
    func repetitions(task: () -> Void) {
        for _ in 0..<self {
            task()
        }
    }
}
///Implementation
3.repetitions({
    print("Hello!")
})

Having said that, I've just had a small play around with your project and what you describe is what's happening:

let foo = ASStaticLayoutSpec() //<ASStaticLayoutSpec: 0x136d39180>, this is passed into the extension.
let bar = foo.foo() //bar equals a new object <ASStaticLayoutSpec: 0x136e3dff0>

I overlooked the creation of the new ASLayoutSpec() which you then call foo on. My mistake.

[hannahmbanana]

@Adlai-Holler: Not sure if you are still incredibly busy. If not, could you test this against your complex project?

[Adlai-Holler]

Hey! Glad to take a look-see, will do it tomorrow morning and report back.

On May 10, 2016, at 8:46 PM, Hannah Troisi [email protected] wrote:

@Adlai-Holler https://github.com/Adlai-Holler: Not sure if you are still incredibly busy. If not, could you test this against your complex project?

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Reply to this email directly or view it on GitHub https://github.com/facebook/AsyncDisplayKit/issues/1109#issuecomment-218354478

[Adlai-Holler]

@hannahmbanana I believe this issue's resolved as far as we can take it – the Swift compiler seems to crash when optimizing the code OP posted, separate from ASDK itself, so we'll have to wait until Apple fixes the radar linked above. @CodeEagle We good?

[hannahmbanana]

@Adlai-Holler: Hmm. I could have sworn that the radar was marked Closed when I checked this yesterday. :) Thanks for checking anyways!

[Adlai-Holler]

Heads up @hannahmbanana OP hit me with the thumbs up so we can close this.