Combination of `~Copyable` + optional chaining + assignment crashes the compiler.

[YOCKOW]

Description

The compiler crashes when you try to assign a value to a property of optional-chained non-copyable type.

Reproduction

struct NonCopyable: ~Copyable {
  var value: Int = 0
}

var nc: NonCopyable? = NonCopyable()
nc?.value = 1

Stack dump

SIL verification failed: instruction isn't dominated by its operand: properlyDominates(valueI, I)
Verifying instruction:
     %18 = unchecked_take_enum_data_addr %9 : $*Optional<NonCopyable>, #Optional.some!enumelt // users: %17, %21
->   destroy_addr %18 : $*NonCopyable             // id: %17
In function:
// main
// Isolation: unspecified
sil [ossa] @main : $@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32 {
bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>):
  alloc_global @$s4main2ncAA11NonCopyableVSgvp    // id: %2
  %3 = global_addr @$s4main2ncAA11NonCopyableVSgvp : $*Optional<NonCopyable> // users: %9, %8
  %4 = metatype $@thin NonCopyable.Type           // user: %6
  // function_ref NonCopyable.init()
  %5 = function_ref @$s4main11NonCopyableVACycfC : $@convention(method) (@thin NonCopyable.Type) -> @owned NonCopyable // user: %6
  %6 = apply %5(%4) : $@convention(method) (@thin NonCopyable.Type) -> @owned NonCopyable // user: %7
  %7 = enum $Optional<NonCopyable>, #Optional.some!enumelt, %6 // user: %8
  store %7 to [init] %3                           // id: %8
  %9 = begin_access [modify] [dynamic] %3         // users: %12, %18, %23, %14
  %10 = integer_literal $Builtin.Int1, -1         // user: %12
  %11 = integer_literal $Builtin.Int1, 0          // user: %12
  %12 = select_enum_addr %9, case #Optional.some!enumelt: %10, default %11 : $Builtin.Int1 // user: %13
  cond_br %12, bb2, bb1                           // id: %13

bb1:                                              // Preds: bb0
  end_access %9                                   // id: %14
  %15 = enum $Optional<()>, #Optional.none!enumelt // user: %16
  br bb3(%15)                                     // id: %16

bb2:                                              // Preds: bb0
  destroy_addr %18                                // id: %17
  %18 = unchecked_take_enum_data_addr %9, #Optional.some!enumelt // users: %17, %21
  %19 = integer_literal $Builtin.Int64, 1         // user: %20
  %20 = struct $Int (%19)                         // user: %22
  %21 = struct_element_addr %18, #NonCopyable.value // user: %22
  store %20 to [trivial] %21                      // id: %22
  end_access %9                                   // id: %23
  %24 = tuple ()                                  // user: %25
  %25 = enum $Optional<()>, #Optional.some!enumelt, %24 // user: %26
  br bb3(%25)                                     // id: %26

bb3(%27 : $Optional<()>):                         // Preds: bb1 bb2
  %28 = integer_literal $Builtin.Int32, 0         // user: %29
  %29 = struct $Int32 (%28)                       // user: %30
  return %29                                      // id: %30
} // end sil function 'main'

Stack dump:
0.	Program arguments: /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/bin/swift-frontend -frontend -interpret _noncopyable-optional_chaining-assignment_.swift -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.2.sdk -color-diagnostics -empty-abi-descriptor -resource-dir /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/lib/swift -no-auto-bridging-header-chaining -module-name main -in-process-plugin-server-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/lib/swift/host/libSwiftInProcPluginServer.dylib -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/local/lib/swift/host/plugins -target-sdk-version 15.2 -target-sdk-name macosx15.2 -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server
1.	Apple Swift version 6.2-dev (LLVM 21406e90d7382d7, Swift 90340a069a706c3)
2.	Compiling with effective version 5.10
3.	While verifying SIL function "@main".
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           0x000000010a1ac184 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x000000010a1aa8b0 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x000000010a1ac7cc SignalHandler(int, __siginfo*, void*) + 296
3  libsystem_platform.dylib 0x000000018f996de4 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018f95ff70 pthread_kill + 288
5  libsystem_c.dylib        0x000000018f86c908 abort + 128
6  swift-frontend           0x000000010595b828 swift::SILModule::print(llvm::raw_ostream&, swift::ModuleDecl*, swift::SILOptions const&, bool) const + 0
7  swift-frontend           0x000000010597d87c (anonymous namespace)::SILVerifier::visitSILInstruction(swift::SILInstruction*) + 1584
8  swift-frontend           0x0000000105968568 swift::SILVisitorBase<(anonymous namespace)::SILVerifier, void>::visitSILBasicBlock(swift::SILBasicBlock*) + 22648
9  swift-frontend           0x0000000105962c30 (anonymous namespace)::SILVerifier::visitSILBasicBlock(swift::SILBasicBlock*) + 24
10 swift-frontend           0x0000000105961590 (anonymous namespace)::SILVerifier::visitSILFunction(swift::SILFunction*) + 10464
11 swift-frontend           0x000000010595b9e0 swift::SILFunction::verify(swift::CalleeCache*, bool, bool, bool) const + 224
12 swift-frontend           0x000000010595e6f4 swift::SILModule::verify(swift::CalleeCache*, bool, bool) const + 192
13 swift-frontend           0x000000010595e5cc swift::SILModule::verify(bool, bool) const + 140
14 swift-frontend           0x0000000104d0f228 swift::CompilerInstance::performSILProcessing(swift::SILModule*) + 148
15 swift-frontend           0x0000000104ad6340 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*) + 820
16 swift-frontend           0x0000000104ad5cf8 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 1320
17 swift-frontend           0x0000000104ae1f48 withSemanticAnalysis(swift::CompilerInstance&, swift::FrontendObserver*, llvm::function_ref<bool (swift::CompilerInstance&)>, bool) + 164
18 swift-frontend           0x0000000104ad76f4 performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 716
19 swift-frontend           0x0000000104ad6f10 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2244
20 swift-frontend           0x000000010488ec8c swift::mainEntry(int, char const**) + 3060
21 dyld                     0x000000018f5e0274 start + 2840

Expected behavior

The compiler doesn't crash.

Environment

Apple Swift version 6.2-dev (LLVM 21406e90d7382d7, Swift 90340a069a706c3)
Target: arm64-apple-macosx15.0
Build config: +assertions

Additional information

This may be related to #75999, but this issue occurs even if you use ! instead of ?.

(Related post: https://forums.swift.org/t/how-can-i-borrow-with-conditional-binding/78759/11)

[tbkka]

CC: @meg-gupta @eeckstein

[eeckstein]

This is a problem in the MoveOnlyChecker

[jameesbrown]

I think It may be limited to globals e.g. this doesn't crash:

struct S: ~Copyable {
  var x: Int
}
func test() {
  var s: S? = S(x: 0)
  s?.x = 1
}
test()

[YOCKOW]

@jameesbrown I think It may be limited to globals

Interesting and weird. The compiler still crashes when it's a stored property of a final class:

struct NonCopyable: ~Copyable {
  var value: Int = 0
}

final class Holder { // The compiler doesn't crash if this is a noncopyable struct.
  var nc: NonCopyable? = NonCopyable()

  func f() {
    nc?.value = 1
  }
}

Stack dump

SIL verification failed: instruction isn't dominated by its operand: properlyDominates(valueI, I)
Verifying instruction:
     %9 = unchecked_take_enum_data_addr %3 : $*Optional<NonCopyable>, #Optional.some!enumelt // users: %8, %12
->   destroy_addr %9 : $*NonCopyable              // id: %8
In function:
// Holder.f()
// Isolation: unspecified
sil hidden [ossa] @$s4main6HolderC1fyyF : $@convention(method) (@guaranteed Holder) -> () {
// %0 "self"                                      // users: %2, %1
bb0(%0 : @guaranteed $Holder):
  debug_value %0, let, name "self", argno 1       // id: %1
  %2 = ref_element_addr %0, #Holder.nc            // user: %3
  %3 = begin_access [modify] [dynamic] %2         // users: %6, %9, %14, %21
  %4 = integer_literal $Builtin.Int1, -1          // user: %6
  %5 = integer_literal $Builtin.Int1, 0           // user: %6
  %6 = select_enum_addr %3, case #Optional.some!enumelt: %4, default %5 : $Builtin.Int1 // user: %7
  cond_br %6, bb1, bb3                            // id: %7

bb1:                                              // Preds: bb0
  destroy_addr %9                                 // id: %8
  %9 = unchecked_take_enum_data_addr %3, #Optional.some!enumelt // users: %8, %12
  %10 = integer_literal $Builtin.Int64, 1         // user: %11
  %11 = struct $Int (%10)                         // user: %13
  %12 = struct_element_addr %9, #NonCopyable.value // user: %13
  store %11 to [trivial] %12                      // id: %13
  end_access %3                                   // id: %14
  %15 = tuple ()                                  // user: %16
  %16 = enum $Optional<()>, #Optional.some!enumelt, %15 // user: %17
  br bb2(%16)                                     // id: %17

bb2(%18 : $Optional<()>):                         // Preds: bb3 bb1
  %19 = tuple ()                                  // user: %20
  return %19                                      // id: %20

bb3:                                              // Preds: bb0
  end_access %3                                   // id: %21
  %22 = enum $Optional<()>, #Optional.none!enumelt // user: %23
  br bb2(%22)                                     // id: %23
} // end sil function '$s4main6HolderC1fyyF'

Stack dump:
0.	Program arguments: /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/bin/swift-frontend -frontend -interpret GHI-80261_NonCopyable-OptionalChaining-Assignment_StoredProperty.swift -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.2.sdk -color-diagnostics -empty-abi-descriptor -resource-dir /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/lib/swift -no-auto-bridging-header-chaining -module-name main -in-process-plugin-server-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/lib/swift/host/libSwiftInProcPluginServer.dylib -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/lib/swift/host/plugins -plugin-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-03-17-a.xctoolchain/usr/local/lib/swift/host/plugins -target-sdk-version 15.2 -target-sdk-name macosx15.2 -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server -external-plugin-path /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/local/lib/swift/host/plugins#/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/bin/swift-plugin-server
1.	Apple Swift version 6.2-dev (LLVM 21406e90d7382d7, Swift 90340a069a706c3)
2.	Compiling with effective version 5.10
3.	While verifying SIL function "@$s4main6HolderC1fyyF".
 for 'f()' (at GHI-80261_NonCopyable-OptionalChaining-Assignment_StoredProperty.swift:8:3)
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           0x0000000105bc0184 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x0000000105bbe8b0 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000105bc07cc SignalHandler(int, __siginfo*, void*) + 296
3  libsystem_platform.dylib 0x000000018f996de4 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018f95ff70 pthread_kill + 288
5  libsystem_c.dylib        0x000000018f86c908 abort + 128
6  swift-frontend           0x000000010136f828 swift::SILModule::print(llvm::raw_ostream&, swift::ModuleDecl*, swift::SILOptions const&, bool) const + 0
7  swift-frontend           0x000000010139187c (anonymous namespace)::SILVerifier::visitSILInstruction(swift::SILInstruction*) + 1584
8  swift-frontend           0x000000010137c568 swift::SILVisitorBase<(anonymous namespace)::SILVerifier, void>::visitSILBasicBlock(swift::SILBasicBlock*) + 22648
9  swift-frontend           0x0000000101376c30 (anonymous namespace)::SILVerifier::visitSILBasicBlock(swift::SILBasicBlock*) + 24
10 swift-frontend           0x0000000101375590 (anonymous namespace)::SILVerifier::visitSILFunction(swift::SILFunction*) + 10464
11 swift-frontend           0x000000010136f9e0 swift::SILFunction::verify(swift::CalleeCache*, bool, bool, bool) const + 224
12 swift-frontend           0x00000001013726f4 swift::SILModule::verify(swift::CalleeCache*, bool, bool) const + 192
13 swift-frontend           0x00000001013725cc swift::SILModule::verify(bool, bool) const + 140
14 swift-frontend           0x0000000100723228 swift::CompilerInstance::performSILProcessing(swift::SILModule*) + 148
15 swift-frontend           0x00000001004ea340 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*) + 820
16 swift-frontend           0x00000001004e9cf8 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 1320
17 swift-frontend           0x00000001004f5f48 withSemanticAnalysis(swift::CompilerInstance&, swift::FrontendObserver*, llvm::function_ref<bool (swift::CompilerInstance&)>, bool) + 164
18 swift-frontend           0x00000001004eb6f4 performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 716
19 swift-frontend           0x00000001004eaf10 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2244
20 swift-frontend           0x00000001002a2c8c swift::mainEntry(int, char const**) + 3060
21 dyld                     0x000000018f5e0274 start + 2840

[Rajveer100]

@YOCKOW
I tried to debug this issue via -Xllvm -sil-print-all flag to see the changes in the SIL IR at each pass. Considering the stack trace, there is a dominance issue and specifically in these passes the changes happen in the consume which I believe the MoveOnlyAddressChecker and MoveOnlyObjectChecker handle to transfer ownership.

From my understanding it looks the destroy shouldn't happen since we aren't really transferring anything and just assigning the value to the object nc as described in the original snippet:

nc?.value = 1

Similar error happens when doing:

var nc1: NonCopyable? = NonCopyable()
nc1?.value = 1

func f(nc1: consuming NonCopyable?) {
  var nc2: NonCopyable? = nc1
}

Or even:

var nc1: NonCopyable? = NonCopyable()
nc1?.value = 1

func f(nc1: consuming NonCopyable?) {
  var nc2: NonCopyable? = NonCopyable(value: nc1!.value)
}

Same issue happens with borrow but commenting out the assignment fixes it. This indeed seems to be a problem only with globals or cases when the object is final and cannot be changed at top level.

Specifically in these passes is where the dominator tree seems broken:

Pass 72:

  *** SIL function after  #72, stage Mandatory Diagnostic Passes + Enabling Optimization Passes, pass 18: LowerTupleAddrConstructor (lower-tuple-addr-constructor)
// main
// Isolation: unspecified
sil [ossa] @main : $@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32 {
bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>):
  alloc_global @$s4main2ncAA11NonCopyableVSgvp    // id: %2
  %3 = global_addr @$s4main2ncAA11NonCopyableVSgvp : $*Optional<NonCopyable> // users: %9, %8
  %4 = metatype $@thin NonCopyable.Type           // user: %6
  // function_ref NonCopyable.init()
  %5 = function_ref @$s4main11NonCopyableVACycfC : $@convention(method) (@thin NonCopyable.Type) -> @owned NonCopyable // user: %6
  %6 = apply %5(%4) : $@convention(method) (@thin NonCopyable.Type) -> @owned NonCopyable // user: %7
  %7 = enum $Optional<NonCopyable>, #Optional.some!enumelt, %6 // user: %8
  store %7 to [init] %3                           // id: %8
  %9 = begin_access [modify] [dynamic] %3         // users: %24, %15, %10
  %10 = mark_unresolved_non_copyable_value [assignable_but_not_consumable] %9 // users: %17, %13
  %11 = integer_literal $Builtin.Int1, -1         // user: %13
  %12 = integer_literal $Builtin.Int1, 0          // user: %13
  %13 = select_enum_addr %10, case #Optional.some!enumelt: %11, default %12 : $Builtin.Int1 // user: %14
  cond_br %13, bb2, bb1                           // id: %14

bb1:                                              // Preds: bb0
  end_access %9                                   // id: %15
  br bb4                                          // id: %16

bb2:                                              // Preds: bb0
  %17 = unchecked_take_enum_data_addr %10, #Optional.some!enumelt // user: %22
  %18 = integer_literal $Builtin.IntLiteral, 1    // user: %21
  %19 = metatype $@thin Int.Type                  // user: %21
  // function_ref Int.init(_builtinIntegerLiteral:)
  %20 = function_ref @$sSi22_builtinIntegerLiteralSiBI_tcfC : $@convention(method) (Builtin.IntLiteral, @thin Int.Type) -> Int // user: %21
  %21 = apply %20(%18, %19) : $@convention(method) (Builtin.IntLiteral, @thin Int.Type) -> Int // user: %23
  %22 = struct_element_addr %17, #NonCopyable.value // user: %23
  store %21 to [trivial] %22                      // id: %23
  end_access %9                                   // id: %24
  %25 = tuple ()                                  // user: %26
  %26 = enum $Optional<()>, #Optional.some!enumelt, %25 // user: %27
  br bb3(%26)                                     // id: %27

bb3(%28 : $Optional<()>):                         // Preds: bb4 bb2
  %29 = integer_literal $Builtin.Int32, 0         // user: %30
  %30 = struct $Int32 (%29)                       // user: %31
  return %30                                      // id: %31

bb4:                                              // Preds: bb1
  %32 = enum $Optional<()>, #Optional.none!enumelt // user: %33
  br bb3(%32)                                     // id: %33
} // end sil function 'main'

And then we destroy %17 before creation as soon as we access value from nc:

Pass 89:

  *** SIL function after  #89, stage Mandatory Diagnostic Passes + Enabling Optimization Passes, pass 21: MoveOnlyChecker (sil-move-only-checker)
// main
// Isolation: unspecified
sil [ossa] @main : $@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32 {
bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>):
  alloc_global @$s4main3nc1AA11NonCopyableVSgvp   // id: %2
  %3 = global_addr @$s4main3nc1AA11NonCopyableVSgvp : $*Optional<NonCopyable> // users: %9, %8
  %4 = metatype $@thin NonCopyable.Type           // user: %6
  // function_ref NonCopyable.init()
  %5 = function_ref @$s4main11NonCopyableVACycfC : $@convention(method) (@thin NonCopyable.Type) -> @owned NonCopyable // user: %6
  %6 = apply %5(%4) : $@convention(method) (@thin NonCopyable.Type) -> @owned NonCopyable // user: %7
  %7 = enum $Optional<NonCopyable>, #Optional.some!enumelt, %6 // user: %8
  store %7 to [init] %3                           // id: %8
  %9 = begin_access [modify] [dynamic] %3         // users: %12, %17, %24, %14
  %10 = integer_literal $Builtin.Int1, -1         // user: %12
  %11 = integer_literal $Builtin.Int1, 0          // user: %12
  %12 = select_enum_addr %9, case #Optional.some!enumelt: %10, default %11 : $Builtin.Int1 // user: %13
  cond_br %12, bb2, bb1                           // id: %13

bb1:                                              // Preds: bb0
  end_access %9                                   // id: %14
  br bb4                                          // id: %15

bb2:                                              // Preds: bb0
  destroy_addr %17                                // id: %16
  %17 = unchecked_take_enum_data_addr %9, #Optional.some!enumelt // users: %16, %22
  %18 = integer_literal $Builtin.IntLiteral, 1    // user: %21
  %19 = metatype $@thin Int.Type                  // user: %21
  // function_ref Int.init(_builtinIntegerLiteral:)
  %20 = function_ref @$sSi22_builtinIntegerLiteralSiBI_tcfC : $@convention(method) (Builtin.IntLiteral, @thin Int.Type) -> Int // user: %21
  %21 = apply %20(%18, %19) : $@convention(method) (Builtin.IntLiteral, @thin Int.Type) -> Int // user: %23
  %22 = struct_element_addr %17, #NonCopyable.value // user: %23
  store %21 to [trivial] %22                      // id: %23
  end_access %9                                   // id: %24
  %25 = tuple ()                                  // user: %26
  %26 = enum $Optional<()>, #Optional.some!enumelt, %25 // user: %27
  br bb3(%26)                                     // id: %27

bb3(%28 : $Optional<()>):                         // Preds: bb4 bb2
  %29 = integer_literal $Builtin.Int32, 0         // user: %30
  %30 = struct $Int32 (%29)                       // user: %31
  return %30                                      // id: %31

bb4:                                              // Preds: bb1
  %32 = enum $Optional<()>, #Optional.none!enumelt // user: %33
  br bb3(%32)                                     // id: %33
} // end sil function 'main'