Compiler crash with associatedtype inferred from some return type + generic constraints

[KeithBauerANZ]

Description

Simplified from an example that came up in SwiftUI, this crashes the compiler:

protocol Q {}

class C {}
class D<T: Q>: C {}

protocol P {
    associatedtype A: C
    func requirement1() -> A
    func requirement2(_: A)
}

struct S<T: Q>: P {
    func requirement1() -> some C { D<T>() }
    func requirement2(_ a: A) {}
}

swiftc CrashInferringAssociatedType.swift
error: compile command failed due to signal 11 (use -v to see invocation)
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.	Program arguments: /Users/<me>/Applications/Xcode-15.0.0-Beta.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file CrashInferringAssociatedType.swift -target arm64-apple-macosx13.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -stack-check -sdk /Users/<me>/Applications/Xcode-15.0.0-Beta.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk -color-diagnostics -new-driver-path /Users/<me>/Applications/Xcode-15.0.0-Beta.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-driver -empty-abi-descriptor -plugin-path /Users/<me>/Applications/Xcode-15.0.0-Beta.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Users/<me>/Applications/Xcode-15.0.0-Beta.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/local/lib/swift/host/plugins -resource-dir /Users/<me>/Applications/Xcode-15.0.0-Beta.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift -module-name CrashInferringAssociatedType -disable-clang-spi -target-sdk-version 14.0 -target-sdk-name macosx14.0 -o /var/folders/jg/3hxr5hxx7hd3kcfjs1c7ylqr0000gp/T/TemporaryDirectory.d28LZd/CrashInferringAssociatedType-1.o
1.	Apple Swift version 5.9 (swiftlang-5.9.0.114.10 clang-1500.0.29.1)
2.	Compiling with the current language version
3.	While evaluating request IRGenRequest(IR Generation for file "CrashInferringAssociatedType.swift")
4.	While emitting IR SIL function "@$s28CrashInferringAssociatedType1SVyxGAA1PA2aEP12requirement2yy1AQzFTW".
 for 'requirement2(_:)' (at CrashInferringAssociatedType.swift:14:5)
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  swift-frontend           0x0000000109c8004c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x0000000109c7f210 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000109c8064c SignalHandler(int) + 352
3  libsystem_platform.dylib 0x000000018cbbea24 _sigtramp + 56
4  swift-frontend           0x0000000104a54038 swift::irgen::CallEmission::emitCallSite() + 52
5  swift-frontend           0x0000000104a56374 swift::irgen::CallEmission::emitToExplosion(swift::irgen::Explosion&, bool) + 2380
6  swift-frontend           0x0000000104c96858 (anonymous namespace)::IRGenSILFunction::visitFullApplySite(swift::FullApplySite) + 4072
7  swift-frontend           0x0000000104c6d110 (anonymous namespace)::IRGenSILFunction::visitSILBasicBlock(swift::SILBasicBlock*) + 2676
8  swift-frontend           0x0000000104c6ab4c swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 11112
9  swift-frontend           0x0000000104ac578c swift::irgen::IRGenerator::emitLazyDefinitions() + 4728
10 swift-frontend           0x0000000104c1a6c0 swift::IRGenRequest::evaluate(swift::Evaluator&, swift::IRGenDescriptor) const + 5852
11 swift-frontend           0x0000000104c67d58 swift::SimpleRequest<swift::IRGenRequest, swift::GeneratedModule (swift::IRGenDescriptor), (swift::RequestFlags)9>::evaluateRequest(swift::IRGenRequest const&, swift::Evaluator&) + 176
12 swift-frontend           0x0000000104c2bfe0 llvm::Expected<swift::IRGenRequest::OutputType> swift::Evaluator::getResultUncached<swift::IRGenRequest>(swift::IRGenRequest const&) + 1516
13 swift-frontend           0x0000000104c1f2ec swift::performIRGeneration(swift::FileUnit*, swift::IRGenOptions const&, swift::TBDGenOptions const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>>, llvm::StringRef, swift::PrimarySpecificPaths const&, llvm::StringRef, llvm::GlobalVariable**) + 264
14 swift-frontend           0x00000001046b5954 generateIR(swift::IRGenOptions const&, swift::TBDGenOptions const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>>, swift::PrimarySpecificPaths const&, llvm::StringRef, llvm::PointerUnion<swift::ModuleDecl*, swift::SourceFile*>, llvm::GlobalVariable*&, llvm::ArrayRef<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>) + 156
15 swift-frontend           0x00000001046b03bc performCompileStepsPostSILGen(swift::CompilerInstance&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>>, llvm::PointerUnion<swift::ModuleDecl*, swift::SourceFile*>, swift::PrimarySpecificPaths const&, int&, swift::FrontendObserver*) + 1596
16 swift-frontend           0x00000001046b306c performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 1748
17 swift-frontend           0x00000001046b1504 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 4216
18 swift-frontend           0x0000000104676d7c swift::mainEntry(int, char const**) + 4112
19 dyld                     0x000000018c837f28 start + 2236
error: fatalError

Environment

swift-driver version: 1.82.2 Apple Swift version 5.9 (swiftlang-5.9.0.114.10 clang-1500.0.29.1)
Target: arm64-apple-macosx13.0

same crash with Xcode 14:

swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
Target: arm64-apple-macosx13.0