[swift-dev] Xcode 8 GM: Compiler segfaults on ExpressibleByArrayLiteral

[Douglas Gregor]

> On Sep 8, 2016, at 6:50 AM, Ole Begemann via swift-dev <swift-dev at swift.org> wrote:
> 
> I'm seeing a segmentation fault when compiling this code with Xcode 8 GM:
> 
> ```
> // stack.swift
> struct Stack<Element> {
>    var elements: [Element] = []
> }
> 
> extension Stack: ExpressibleByArrayLiteral {
>    init(arrayLiteral elements: Element...) {
>        self.elements = elements
>    }
> }
> ```
> 
> ---
> 
> This is my Swift version (Xcode 8 GM):
> 
> ```
> $ xcrun swift --version
> Apple Swift version 3.0 (swiftlang-800.0.46.2 clang-800.0.38)
> Target: x86_64-apple-macosx10.9
> ```
> 
> I'm on OS X 10.11.6.
> 
> ---
> 
> Compiling with `xcrun swift stack.swift`, I see this:
> 
> ```
> $ xcrun swift stack.swift
> 0  swift                    0x000000010558fb6d PrintStackTraceSignalHandler(void*) + 45
> 1  swift                    0x000000010558f5b6 SignalHandler(int) + 470
> 2  libsystem_platform.dylib 0x00007fff8e5a952a _sigtramp + 26
> 3  libsystem_platform.dylib 0x00007fff5d2ca6d0 _sigtramp + 3469873600
> 4  swift                    0x0000000102a6d8b9 swift::irgen::IRGenFunction::emitTypeMetadataRef(swift::CanType) + 73
> 5  swift                    0x0000000102aab07d void llvm::function_ref<void (swift::irgen::GenericRequirement)>::callback_fn<(anonymous namespace)::EmitPolymorphicArguments::emit(swift::CanTypeWrapper<swift::SILFunctionType>, llvm::ArrayRef<swift::Substitution>, swift::irgen::WitnessMetadata*, swift::irgen::Explosion&)::$_14>(long, swift::irgen::GenericRequirement) + 861
> 6  swift                    0x0000000102aa09e1 (anonymous namespace)::PolymorphicConvention::enumerateRequirements(llvm::function_ref<void (swift::irgen::GenericRequirement)> const&) + 129
> 7  swift                    0x0000000102aaabdb swift::irgen::emitPolymorphicArguments(swift::irgen::IRGenFunction&, swift::CanTypeWrapper<swift::SILFunctionType>, swift::CanTypeWrapper<swift::SILFunctionType>, llvm::ArrayRef<swift::Substitution>, swift::irgen::WitnessMetadata*, swift::irgen::Explosion&) + 459
> 8  swift                    0x0000000102b074f5 (anonymous namespace)::IRGenSILFunction::visitFullApplySite(swift::FullApplySite) + 2997
> 9  swift                    0x0000000102af2268 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 9080
> 10 swift                    0x0000000102a184d0 swift::irgen::IRGenerator::emitLazyDefinitions() + 5216
> 11 swift                    0x0000000102ad819b performIRGeneration(swift::IRGenOptions&, swift::ModuleDecl*, swift::SILModule*, llvm::StringRef, llvm::LLVMContext&, swift::SourceFile*, unsigned int) + 1723
> 12 swift                    0x0000000102ad6507 swift::performIRGeneration(swift::IRGenOptions&, swift::ModuleDecl*, swift::SILModule*, llvm::StringRef, llvm::LLVMContext&) + 1527
> 13 swift                    0x00000001029baa7b swift::RunImmediately(swift::CompilerInstance&, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, swift::IRGenOptions&, swift::SILOptions const&) + 187
> 14 swift                    0x00000001029a607e performCompile(swift::CompilerInstance&, swift::CompilerInvocation&, llvm::ArrayRef<char const*>, int&, swift::FrontendObserver*) + 23358
> 15 swift                    0x000000010299e265 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 17029
> 16 swift                    0x000000010295b82d main + 8685
> 17 libdyld.dylib            0x00007fff91eef5ad start + 1
> 18 libdyld.dylib            0x000000000000000c start + 1846610528
> Stack dump:
> 0.      Program arguments: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -interpret stack.swift -target x86_64-apple-macosx10.9 -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -color-diagnostics -module-name stack
> 1.      While emitting IR SIL function @_TFV5stack5StackCft12arrayLiteralGSax__GS0_x_ for 'init' at stack.swift:6:5
> [1]    38858 segmentation fault  xcrun swift stack.swift
> $
> ```
> 
> ---
> 
> Regression:
> I observed the same behavior at least in Xcode 8b6 and b5. I did not report this earlier because the problem did not occur in recent Swift snapshots. The oldest one I still have installed is `DEVELOPMENT-SNAPSHOT-2016-08-07-a`, and with that one it already compiles fine:
> 
> ```
> # DEVELOPMENT-SNAPSHOT-2016-08-07-a
> $ swift --version
> Apple Swift version 3.0-dev (LLVM 17c4c6cf7a, Clang 4ca9e01a7c, Swift 13a9908f8d)
> Target: x86_64-apple-macosx10.9
> 
> $ swift ~/code/stack.swift
> $
> ```
> 
> ---
> 
> Workaround:
> It compiles fine if I rewrite the `ExpressibleByArrayLiteral` initializer like this:
> 
> ```
> struct Stack<Element> {
>    var elements: [Element] = []
> }
> 
> extension Stack: ExpressibleByArrayLiteral {
>    init(arrayLiteral elements: Element...) {
>        self.init(elements: elements)
>    }
> }
> ```
> 
> Or alternatively, provide an explicit initializer for the struct:
> 
> ```
> struct Stack<Element> {
>    var elements: [Element]
>    init(elements: [Element]) {
>        self.elements = elements
>    }
> }
> 
> extension Stack: ExpressibleByArrayLiteral {
>    init(arrayLiteral elements: Element...) {
>        self.elements = elements
>    }
> }
> ```
> 
> ---
> 
> Is this something for Radar or bugs.swift.org?

FWIW, it’s actually fixed in master (probably due to Slava’s recent work on the generics system). The primary benefit to filing a radar at this point is that you’ll get notified when the fix makes it into an Xcode release.

	- Doug