$ swift -Xfrontend -enable-experimental-concurrency test.swift
test.swift:5:13: warning: local var 'result' is unsafe to reference in code that may execute concurrently
            result = .success(try await asyncFun())
            ^
test.swift:2:9: note: var declared here
    var result: Result<R, Error>? = nil
        ^
test.swift:7:13: warning: local var 'result' is unsafe to reference in code that may execute concurrently
            result = .failure(error)
            ^
test.swift:2:9: note: var declared here
    var result: Result<R, Error>? = nil
        ^
Assertion failed: (llvm::isa<llvm::Argument>(Storage) && "arg expected to be load from inside %swift.context"), function visitDebugValueAddrInst, file /Users/buildnode/jenkins/workspace/oss-swift-package-macos/swift/lib/IRGen/IRGenSIL.cpp, line 4363.
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the project and the crash backtrace.
Stack dump:
0.  Program arguments: /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2021-01-14-a.xctoolchain/usr/bin/swift-frontend -frontend -interpret test.swift -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -color-diagnostics -enable-experimental-concurrency -target-sdk-version 11.1 -module-name test
1.  Apple Swift version 5.4-dev (LLVM 4a2039285189ee5, Swift edcefe353246b16)
2.  While running user code "test.swift"
3.  While evaluating request IRGenRequest(IR Generation for module test)
4.  While emitting IR SIL function "@$s4test24runAsyncAndBlockThrowingyxxyYKcKlFyyYcfU_".
 for expression at [test.swift:3:22 - line:9:5] RangeText="{
        do {
            result = .success(try await asyncFun())
        } catch {
            result = .failure(error)
        }
    "
0  swift-frontend           0x00000001144bac35 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift-frontend           0x00000001144b9e95 llvm::sys::RunSignalHandlers() + 85
2  swift-frontend           0x00000001144bb206 SignalHandler(int) + 262
3  libsystem_platform.dylib 0x00007fff6b5ee5fd _sigtramp + 29
4  libdyld.dylib            0x00007fff6b3f478f dyldGlobalLockRelease() + 0
5  libsystem_c.dylib        0x00007fff6b4c4808 abort + 120
6  libsystem_c.dylib        0x00007fff6b4c3ac6 err + 0
7  swift-frontend           0x0000000114615943 swift::SILInstructionVisitor<(anonymous namespace)::IRGenSILFunction, void>::visit(swift::SILInstruction*) (.cold.713) + 35
8  swift-frontend           0x0000000110032eee swift::SILInstructionVisitor<(anonymous namespace)::IRGenSILFunction, void>::visit(swift::SILInstruction*) + 75150
9  swift-frontend           0x000000011001c08f (anonymous namespace)::IRGenSILFunction::emitSILFunction() + 7983
10 swift-frontend           0x0000000110019c03 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 1523
11 swift-frontend           0x000000010fef47fb swift::irgen::IRGenerator::emitLazyDefinitions() + 1819
12 swift-frontend           0x000000010ffde5e7 swift::IRGenRequest::evaluate(swift::Evaluator&, swift::IRGenDescriptor) const + 2263
13 swift-frontend           0x000000011001925d swift::GeneratedModule swift::SimpleRequest<swift::IRGenRequest, swift::GeneratedModule (swift::IRGenDescriptor), (swift::RequestFlags)9>::callDerived<0ul>(swift::Evaluator&, std::__1::integer_sequence<unsigned long, 0ul>) const + 157
14 swift-frontend           0x000000011001917e swift::SimpleRequest<swift::IRGenRequest, swift::GeneratedModule (swift::IRGenDescriptor), (swift::RequestFlags)9>::evaluateRequest(swift::IRGenRequest const&, swift::Evaluator&) + 14
15 swift-frontend           0x000000010ffea108 llvm::Expected<swift::IRGenRequest::OutputType> swift::Evaluator::getResultUncached<swift::IRGenRequest>(swift::IRGenRequest const&) + 408
16 swift-frontend           0x000000010ffdf7a0 swift::performIRGeneration(swift::ModuleDecl*, swift::IRGenOptions const&, swift::TBDGenOptions const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >, llvm::StringRef, swift::PrimarySpecificPaths const&, llvm::ArrayRef<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, llvm::GlobalVariable**) + 576
17 swift-frontend           0x000000010fd3d03d 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 const&, swift::SILOptions const&, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule> >&&) + 349
18 swift-frontend           0x000000010fd05101 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*) + 1953
19 swift-frontend           0x000000010fd0473c performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 636
20 swift-frontend           0x000000010fcf937e swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 5214
21 swift-frontend           0x000000010fc95642 main + 866
22 libdyld.dylib            0x00007fff6b3f5cc9 start + 1
23 libdyld.dylib            0x000000000000000d start + 18446603338716848965
Abort trap: 6