Crash in silgen due to missed / failed typecheck

[asl]

Description

Consider the reproducer. It crashes with llvm_unreachable in SILgen:

<unknown>:0: error: fatal error encountered during compilation; please submit a bug report (https://swift.org/contributing/#reporting-bugs)
<unknown>:0: note: unsupported collection upcast kind

At the same time if the consider the almost equivalent code (second variant), then it correctly diagnoses the problem:

 6 | }
 7 | let pb = pullback(at: 1.0, of: testFunc)
 8 | print(pb(.init(1.0)) == 3.0)
   |                         `- error: cannot convert value of type 'Double' to expected argument type 'Optional<Double>.TangentVector'

Somehow the typechecker is confused in nested pullback call inside print and produces the following type-checked expression (produced via -debug-constraints):

(call_expr type="()" location=opt2.swift:9:1 range=[opt2.swift:9:1 - line:9:57] isolation_crossing="none"
  (declref_expr type="(Any..., String, String) -> ()" location=opt2.swift:9:1 range=[opt2.swift:9:1 - line:9:1] decl="Swift.(file).print(_:separator:terminator:)" function_ref=single)
  (argument_list labels="_:separator:terminator:"
    (argument
      (vararg_expansion_expr implicit type="Any..." location=opt2.swift:9:7 range=[opt2.swift:9:7 - line:9:54]
        (array_expr implicit type="Any..." location=opt2.swift:9:7 range=[opt2.swift:9:7 - line:9:54] initializer="**NULL**"
          (erasure_expr implicit type="Any" location=opt2.swift:9:51 range=[opt2.swift:9:7 - line:9:54]
            (builtin_conformance type="Bool" protocol="Copyable")
            (builtin_conformance type="Bool" protocol="Escapable")
            (binary_expr type="Bool" location=opt2.swift:9:51 range=[opt2.swift:9:7 - line:9:54] isolation_crossing="none"
              (dot_syntax_call_expr implicit type="(Double.TangentVector, Double.TangentVector) -> Bool" location=opt2.swift:9:51 range=[opt2.swift:9:51 - line:9:51] isolation_crossing="none"
                (declref_expr type="(Double.TangentVector.Type) -> (Double.TangentVector, Double.TangentVector) -> Bool" location=opt2.swift:9:51 range=[opt2.swift:9:51 - line:9:51] decl="Swift.(file).FloatingPoint extension.== [with (substitution_map generic_signature=<Self where Self : FloatingPoint> Self -> Double)]" function_ref=single)
                (argument_list implicit
                  (argument
                    (type_expr implicit type="Double.TangentVector.Type" location=opt2.swift:9:51 range=[opt2.swift:9:51 - line:9:51] typerepr="Double.TangentVector"))))
              (argument_list implicit
                (argument
                  (call_expr type="Double.TangentVector" location=opt2.swift:9:7 range=[opt2.swift:9:7 - line:9:49] isolation_crossing="none"
                    (call_expr type="(Optional<Double>.TangentVector) -> Double.TangentVector" location=opt2.swift:9:7 range=[opt2.swift:9:7 - line:9:37] isolation_crossing="none"
                      (declref_expr type="(Double, @differentiable(reverse) (Double) -> Double?) -> (Optional<Double>.TangentVector) -> Double.TangentVector" location=opt2.swift:9:7 range=[opt2.swift:9:7 - line:9:7] decl="_Differentiation.(file).pullback(at:of:) [with (substitution_map generic_signature=<T, R where T : Differentiable, R : Differentiable> T -> Double R -> Double?)]" function_ref=double)
                      (argument_list labels="at:of:"
                        (argument label="at"
                          (float_literal_expr type="Double" location=opt2.swift:9:20 range=[opt2.swift:9:20 - line:9:20] value="1.0" builtin_initializer="Swift.(file).Double extension.init(_builtinFloatLiteral:)" initializer="**NULL**" builtin_type="Builtin.FPIEEE64"))
                        (argument label="of"
                          (function_conversion_expr implicit type="@differentiable(reverse) (Double) -> Double?" location=opt2.swift:9:29 range=[opt2.swift:9:29 - line:9:29]
                            (differentiable_function implicit type="@differentiable(reverse) (Double) -> Double?" location=opt2.swift:9:29 range=[opt2.swift:9:29 - line:9:29]
                              (declref_expr type="(Double?) -> Double?" location=opt2.swift:9:29 range=[opt2.swift:9:29 - line:9:29] decl="opt2.(file).testFunc@opt2.swift:4:6" function_ref=unapplied))))))
                    (argument_list
                      (argument
                        (call_expr type="Optional<Double>.TangentVector" location=opt2.swift:9:40 range=[opt2.swift:9:39 - line:9:48] isolation_crossing="none"
                          (constructor_ref_call_expr type="(Double.TangentVector?) -> Optional<Double>.TangentVector" location=opt2.swift:9:40 range=[opt2.swift:9:39 - line:9:40] isolation_crossing="none"
                            (declref_expr type="(Optional<Double>.TangentVector.Type) -> (Double.TangentVector?) -> Optional<Double>.TangentVector" location=opt2.swift:9:40 range=[opt2.swift:9:40 - line:9:40] decl="_Differentiation.(file).Optional extension.TangentVector.init(_:) [with (substitution_map generic_signature=<Wrapped where Wrapped : Differentiable> Wrapped -> Double)]" function_ref=single)
                            (argument_list implicit
                              (argument
                                (type_expr implicit type="Optional<Double>.TangentVector.Type" location=opt2.swift:9:39 range=[opt2.swift:9:39 - line:9:39] typerepr="Optional<Double>.TangentVector"))))
                          (argument_list
                            (argument
                              (inject_into_optional implicit type="Double.TangentVector?" location=opt2.swift:9:45 range=[opt2.swift:9:45 - line:9:45]
                                (float_literal_expr type="Double" location=opt2.swift:9:45 range=[opt2.swift:9:45 - line:9:45] value="1.0" builtin_initializer="Swift.(file).Double extension.init(_builtinFloatLiteral:)" initializer="**NULL**" builtin_type="Builtin.FPIEEE64")))))))))
                (argument
                  (float_literal_expr type="Double" location=opt2.swift:9:54 range=[opt2.swift:9:54 - line:9:54] value="3.0" builtin_initializer="Swift.(file).Double extension.init(_builtinFloatLiteral:)" initializer="**NULL**" builtin_type="Builtin.FPIEEE64"))))))))
    (argument label="separator"
      (default_argument_expr implicit type="String" location=opt2.swift:9:6 range=[opt2.swift:9:6 - line:9:6] default_args_owner="Swift.(file).print(_:separator:terminator:)" param=1))
    (argument label="terminator"
      (default_argument_expr implicit type="String" location=opt2.swift:9:6 range=[opt2.swift:9:6 - line:9:6] default_args_owner="Swift.(file).print(_:separator:terminator:)" param=2))))

Reproduction

import _Differentiation

@differentiable(reverse)
func testFunc(_ x: Double?) -> Double? {
    x! * x! * x!
}
print(pullback(at: 1.0, of: testFunc)(.init(1.0)) == 3.0)

correctly diagnosed variant:

import _Differentiation

@differentiable(reverse)
func testFunc(_ x: Double?) -> Double? {
    x! * x! * x!
}
let pb = pullback(at: 1.0, of: testFunc)
print(pb(.init(1.0)) == 3.0)

Stack dump

Stack dump:
0.	Program arguments: /Users/asl/Projects/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/bin/swift-frontend -frontend -c -primary-file opt2.swift -target arm64-apple-macosx15.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.sdk -color-diagnostics -empty-abi-descriptor -resource-dir /Users/asl/Projects/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/lib/swift -Xllvm -debug-only=differentiation -module-name opt2 -debug-constraints -in-process-plugin-server-path /Users/asl/Projects/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/lib/swift/host/libSwiftInProcPluginServer.dylib -plugin-path /Users/asl/Projects/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/lib/swift/host/plugins -plugin-path /Users/asl/Projects/swift-project/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/local/lib/swift/host/plugins -target-sdk-version 15.1 -target-sdk-name macosx15.1 -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 -o /var/folders/jm/hc1mgp813kb_9x8z1kdwvqjc0000gn/T/TemporaryDirectory.11ewBS/opt2-1.o
1.	Swift version 6.1-dev (LLVM 42f3e8ef873e24d, Swift 0c8afd34d4d9460)
2.	Compiling with effective version 5.10
3.	While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "opt2.swift")
4.	While emitting reabstraction thunk in SIL function "@$sSdSgAAIegyd_SdAAIegyd_TR".
 for <<debugloc at "<compiler-generated>":0:0>>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           0x0000000105690af4 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x000000010568f244 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x0000000105691138 SignalHandler(int) + 292
3  libsystem_platform.dylib 0x000000019cff0184 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000019cfbaf70 pthread_kill + 288
5  libsystem_c.dylib        0x000000019cec7908 abort + 128
6  swift-frontend           0x0000000100732ee4 swift::DiagnosticHelper::create(swift::CompilerInstance&, llvm::raw_pwrite_stream&, bool) + 0
7  swift-frontend           0x0000000105611144 llvm::report_fatal_error(llvm::Twine const&, bool) + 256
8  swift-frontend           0x0000000105611044 llvm::report_fatal_error(llvm::Twine const&, bool) + 0
9  swift-frontend           0x0000000100b776dc (anonymous namespace)::Transform::~Transform() + 0
10 swift-frontend           0x0000000100b8134c (anonymous namespace)::TranslateArguments::processSingle(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::ManagedValue, (anonymous namespace)::ParamInfo) + 800
11 swift-frontend           0x0000000100b7f834 (anonymous namespace)::ExpanderBase<(anonymous namespace)::TranslateArguments, (anonymous namespace)::ParamInfo>::expand(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType) + 680
12 swift-frontend           0x0000000100b85aa4 (anonymous namespace)::TranslateArguments::expandParam(swift::Lowering::AbstractionPattern, swift::AnyFunctionType::CanParam, swift::Lowering::AbstractionPattern, swift::AnyFunctionType::CanParam) + 208
13 swift-frontend           0x0000000100b792b0 (anonymous namespace)::TranslateArguments::process(swift::Lowering::AbstractionPattern, swift::ArrayRefView<swift::AnyFunctionType::Param, swift::AnyFunctionType::CanParam, swift::AnyFunctionType::CanParam::getFromParam(swift::AnyFunctionType::Param const&), true>, swift::Lowering::AbstractionPattern, swift::ArrayRefView<swift::AnyFunctionType::Param, swift::AnyFunctionType::CanParam, swift::AnyFunctionType::CanParam::getFromParam(swift::AnyFunctionType::Param const&), true>, bool) + 3036
14 swift-frontend           0x0000000100b7cc54 buildThunkBody(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::CanTypeWrapper<swift::SILFunctionType>, swift::CanType, llvm::function_ref<void (swift::Lowering::SILGenFunction&)>) + 984
15 swift-frontend           0x0000000100b7e5f0 createThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::TypeLowering const&) + 2512
16 swift-frontend           0x0000000100b7e2f0 createThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::TypeLowering const&) + 1744
17 swift-frontend           0x0000000100b76994 (anonymous namespace)::Transform::transform(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 2740
18 swift-frontend           0x0000000100b75ec0 swift::Lowering::SILGenFunction::emitTransformedValue(swift::SILLocation, swift::Lowering::ManagedValue, swift::CanType, swift::CanType, swift::Lowering::SGFContext) + 232
19 swift-frontend           0x0000000100b1cfc0 (anonymous namespace)::RValueEmitter::visitFunctionConversionExpr(swift::FunctionConversionExpr*, swift::Lowering::SGFContext) + 1352
20 swift-frontend           0x0000000100b0c630 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 56
21 swift-frontend           0x0000000100af09a8 swift::Lowering::SILGenFunction::emitConvertedRValue(swift::SILLocation, swift::Lowering::Conversion const&, swift::Lowering::SGFContext, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::SGFContext)>) + 312
22 swift-frontend           0x0000000100a8af4c swift::Lowering::ArgumentSource::getConverted(swift::Lowering::SILGenFunction&, swift::Lowering::Conversion const&, swift::Lowering::SGFContext) && + 184
23 swift-frontend           0x0000000100abf548 (anonymous namespace)::ArgEmitter::emit(swift::Lowering::ArgumentSource&&, swift::Lowering::AbstractionPattern, std::__1::optional<swift::AnyFunctionType::Param>) + 3912
24 swift-frontend           0x0000000100ab1364 (anonymous namespace)::ArgEmitter::emitSingleArg(swift::Lowering::ArgumentSource&&, swift::Lowering::AbstractionPattern, std::__1::optional<swift::AnyFunctionType::Param>) + 312
25 swift-frontend           0x0000000100abe014 (anonymous namespace)::ArgEmitter::emitPreparedArgs(swift::Lowering::PreparedArguments&&, swift::Lowering::AbstractionPattern) + 192
26 swift-frontend           0x0000000100ac87d4 (anonymous namespace)::CallSite::emit(swift::Lowering::SILGenFunction&, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::SILFunctionType>, (anonymous namespace)::ParamLowering&, llvm::SmallVectorImpl<swift::Lowering::ManagedValue>&, llvm::SmallVectorImpl<(anonymous namespace)::DelayedArgument>&, swift::ForeignInfo const&) && + 532
27 swift-frontend           0x0000000100ac82dc (anonymous namespace)::CallEmission::emitArgumentsForNormalApply(swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::SILFunctionType>, swift::ForeignInfo const&, llvm::SmallVectorImpl<swift::Lowering::ManagedValue>&, std::__1::optional<swift::SILLocation>&) + 968
28 swift-frontend           0x0000000100ab4988 (anonymous namespace)::CallEmission::apply(swift::Lowering::SGFContext) + 1784
29 swift-frontend           0x0000000100ab3048 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 2044
30 swift-frontend           0x0000000100b0c630 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 56
31 swift-frontend           0x0000000100ac656c (anonymous namespace)::SILGenApply::visitExpr(swift::Expr*) + 44
32 swift-frontend           0x0000000100ab2a40 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 500
33 swift-frontend           0x0000000100b0c630 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 56
34 swift-frontend           0x0000000100abf47c (anonymous namespace)::ArgEmitter::emit(swift::Lowering::ArgumentSource&&, swift::Lowering::AbstractionPattern, std::__1::optional<swift::AnyFunctionType::Param>) + 3708
35 swift-frontend           0x0000000100ab1364 (anonymous namespace)::ArgEmitter::emitSingleArg(swift::Lowering::ArgumentSource&&, swift::Lowering::AbstractionPattern, std::__1::optional<swift::AnyFunctionType::Param>) + 312
36 swift-frontend           0x0000000100abe014 (anonymous namespace)::ArgEmitter::emitPreparedArgs(swift::Lowering::PreparedArguments&&, swift::Lowering::AbstractionPattern) + 192
37 swift-frontend           0x0000000100ac87d4 (anonymous namespace)::CallSite::emit(swift::Lowering::SILGenFunction&, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::SILFunctionType>, (anonymous namespace)::ParamLowering&, llvm::SmallVectorImpl<swift::Lowering::ManagedValue>&, llvm::SmallVectorImpl<(anonymous namespace)::DelayedArgument>&, swift::ForeignInfo const&) && + 532
38 swift-frontend           0x0000000100ac82dc (anonymous namespace)::CallEmission::emitArgumentsForNormalApply(swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::SILFunctionType>, swift::ForeignInfo const&, llvm::SmallVectorImpl<swift::Lowering::ManagedValue>&, std::__1::optional<swift::SILLocation>&) + 968
39 swift-frontend           0x0000000100ab4988 (anonymous namespace)::CallEmission::apply(swift::Lowering::SGFContext) + 1784
40 swift-frontend           0x0000000100ab3048 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 2044
41 swift-frontend           0x0000000100b0c630 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 56
42 swift-frontend           0x0000000100b25d48 swift::Lowering::ManagedValue llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SGFContext)>::callback_fn<(anonymous namespace)::RValueEmitter::visitErasureExpr(swift::ErasureExpr*, swift::Lowering::SGFContext)::$_0>(long, swift::Lowering::SGFContext) + 68
43 swift-frontend           0x0000000100af4970 void llvm::function_ref<void (swift::SILValue)>::callback_fn<swift::Lowering::SILGenFunction::emitExistentialErasure(swift::SILLocation, swift::CanType, swift::Lowering::TypeLowering const&, swift::Lowering::TypeLowering const&, llvm::ArrayRef<swift::ProtocolConformanceRef>, swift::Lowering::SGFContext, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SGFContext)>, bool)::$_3>(long, swift::SILValue) + 156
44 swift-frontend           0x0000000100ad7b64 swift::Lowering::SILGenBuilder::bufferForExpr(swift::SILLocation, swift::SILType, swift::Lowering::TypeLowering const&, swift::Lowering::SGFContext, llvm::function_ref<void (swift::SILValue)>) + 136
45 swift-frontend           0x0000000100aefc44 swift::Lowering::SILGenFunction::emitExistentialErasure(swift::SILLocation, swift::CanType, swift::Lowering::TypeLowering const&, swift::Lowering::TypeLowering const&, llvm::ArrayRef<swift::ProtocolConformanceRef>, swift::Lowering::SGFContext, llvm::function_ref<swift::Lowering::ManagedValue (swift::Lowering::SGFContext)>, bool) + 2452
46 swift-frontend           0x0000000100b1dd90 (anonymous namespace)::RValueEmitter::visitErasureExpr(swift::ErasureExpr*, swift::Lowering::SGFContext) + 392
47 swift-frontend           0x0000000100b09d90 swift::Lowering::SILGenFunction::emitExprInto(swift::Expr*, swift::Lowering::Initialization*, std::__1::optional<swift::SILLocation>) + 156
48 swift-frontend           0x0000000100a8b068 swift::Lowering::ArgumentSource::forwardInto(swift::Lowering::SILGenFunction&, swift::Lowering::Initialization*) && + 164
49 swift-frontend           0x0000000100a8b5fc swift::Lowering::ArgumentSource::forwardInto(swift::Lowering::SILGenFunction&, swift::Lowering::AbstractionPattern, swift::Lowering::Initialization*, swift::Lowering::TypeLowering const&) && + 256
50 swift-frontend           0x0000000100b233a8 (anonymous namespace)::RValueEmitter::visitCollectionExpr(swift::CollectionExpr*, swift::Lowering::SGFContext) + 1072
51 swift-frontend           0x0000000100b0c630 swift::Lowering::SILGenFunction::emitRValueAsSingleValue(swift::Expr*, swift::Lowering::SGFContext) + 56
52 swift-frontend           0x0000000100abf2c4 (anonymous namespace)::ArgEmitter::emit(swift::Lowering::ArgumentSource&&, swift::Lowering::AbstractionPattern, std::__1::optional<swift::AnyFunctionType::Param>) + 3268
53 swift-frontend           0x0000000100ab1364 (anonymous namespace)::ArgEmitter::emitSingleArg(swift::Lowering::ArgumentSource&&, swift::Lowering::AbstractionPattern, std::__1::optional<swift::AnyFunctionType::Param>) + 312
54 swift-frontend           0x0000000100abe014 (anonymous namespace)::ArgEmitter::emitPreparedArgs(swift::Lowering::PreparedArguments&&, swift::Lowering::AbstractionPattern) + 192
55 swift-frontend           0x0000000100ac87d4 (anonymous namespace)::CallSite::emit(swift::Lowering::SILGenFunction&, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::SILFunctionType>, (anonymous namespace)::ParamLowering&, llvm::SmallVectorImpl<swift::Lowering::ManagedValue>&, llvm::SmallVectorImpl<(anonymous namespace)::DelayedArgument>&, swift::ForeignInfo const&) && + 532
56 swift-frontend           0x0000000100ac82dc (anonymous namespace)::CallEmission::emitArgumentsForNormalApply(swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::SILFunctionType>, swift::ForeignInfo const&, llvm::SmallVectorImpl<swift::Lowering::ManagedValue>&, std::__1::optional<swift::SILLocation>&) + 968
57 swift-frontend           0x0000000100ab4988 (anonymous namespace)::CallEmission::apply(swift::Lowering::SGFContext) + 1784
58 swift-frontend           0x0000000100ab3048 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 2044
59 swift-frontend           0x0000000100b0cbfc swift::Lowering::SILGenFunction::emitIgnoredExpr(swift::Expr*) + 900
60 swift-frontend           0x0000000100ba2528 swift::Lowering::SILGenTopLevel::visitTopLevelCodeDecl(swift::TopLevelCodeDecl*) + 248
61 swift-frontend           0x0000000100ba0b64 swift::Lowering::SILGenTopLevel::visitSourceFile(swift::SourceFile*) + 100
62 swift-frontend           0x0000000100ba02f4 swift::Lowering::SILGenModule::emitEntryPoint(swift::SourceFile*, swift::SILFunction*) + 764
63 swift-frontend           0x0000000100ba1e58 swift::Lowering::SILGenModule::emitEntryPoint(swift::SourceFile*) + 264
64 swift-frontend           0x0000000100aa6430 swift::Lowering::SILGenModule::emitSourceFile(swift::SourceFile*) + 616
65 swift-frontend           0x0000000100aa6758 swift::ASTLoweringRequest::evaluate(swift::Evaluator&, swift::ASTLoweringDescriptor) const + 616
66 swift-frontend           0x0000000100b937e8 swift::SimpleRequest<swift::ASTLoweringRequest, std::__1::unique_ptr<swift::SILModule, std::__1::default_delete<swift::SILModule>> (swift::ASTLoweringDescriptor), (swift::RequestFlags)17>::evaluateRequest(swift::ASTLoweringRequest const&, swift::Evaluator&) + 132
67 swift-frontend           0x0000000100aaa5b8 swift::ASTLoweringRequest::OutputType swift::Evaluator::getResultUncached<swift::ASTLoweringRequest, swift::ASTLoweringRequest::OutputType swift::evaluateOrFatal<swift::ASTLoweringRequest>(swift::Evaluator&, swift::ASTLoweringRequest)::'lambda'()>(swift::ASTLoweringRequest const&, swift::ASTLoweringRequest::OutputType swift::evaluateOrFatal<swift::ASTLoweringRequest>(swift::Evaluator&, swift::ASTLoweringRequest)::'lambda'()) + 324
68 swift-frontend           0x0000000100aa6ce8 swift::performASTLowering(swift::FileUnit&, swift::Lowering::TypeConverter&, swift::SILOptions const&, swift::IRGenOptions const*) + 88
69 swift-frontend           0x000000010051b0fc swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 404
70 swift-frontend           0x00000001005277f8 withSemanticAnalysis(swift::CompilerInstance&, swift::FrontendObserver*, llvm::function_ref<bool (swift::CompilerInstance&)>, bool) + 164
71 swift-frontend           0x000000010051cfbc performCompile(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 700
72 swift-frontend           0x000000010051c6dc swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2392
73 swift-frontend           0x00000001002fe238 swift::mainEntry(int, char const**) + 3052
74 dyld                     0x000000019cc38274 start + 2840

Expected behavior

Correct diagnostics is emitted

Environment

Swift version 6.1-dev (LLVM 42f3e8ef873e24d, Swift 0c8afd3)
Target: arm64-apple-macosx15.0

Additional information

No response

[hamishknight]

Minimized a bit:

import _Differentiation

func foo<T, R>(_ fn: @differentiable(reverse) (T) -> R) -> T {}

@differentiable(reverse)
func testFunc(_ x: Double?) -> Double? {}

let _: Double = foo(testFunc)

The issue here is that the type-checker is implicitly converting testFunc from (Double?) -> Double? to (Double) -> Double?, but it seems like that's unsupported by AutoDiff, should maybeDiagnoseUnsupportedDifferentiableConversion be diagnosing here?

[asl]

@hamishknight Thanks! I am a bit confused. The crash is inside silgen, so no autodiff is involved (yet) here. Also, why the case with outlined pullback operator call is correctly diagnosed? What is the different wrt print here?

[hamishknight]

@asl It looks like it's crashing in createDifferentiableFunctionThunk due to an unhandled type mismatch. The outlined case works because there's no type context forcing the type-checker to convert testFunc, so it remains (Double?) -> Double?; the minimized test case stops crashing too once you remove the : Double type annotation

[asl]

@hamishknight Thanks! For some reasons I did not see createDifferentiableFunctionThunk in the stack trace and thought that it is an ordinary silgen code... Then things started to make sense to me. So, we first deduce that the return type being Double and constraint T to it, then introduce the function conversion.

I need to think if this something to be diagnosed, or the thunk generation to be extended.

[hamishknight]

For some reasons I did not see createDifferentiableFunctionThunk in the stack trace

Looks like it gets inlined away in a release build, but you should see it in a debug build:

<unknown>:0: error: fatal error encountered during compilation; please submit a bug report (https://swift.org/contributing/#reporting-bugs)
<unknown>:0: note: unsupported collection upcast kind
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
0.      Program arguments: ./swift -frontend -typecheck /Users/hamish/src/swift-test-arena/main.swift -sdk /Users/hamish/src/MacOSX.sdk -debug-diagnostic-names -diagnostic-style=llvm -emit-sil
1.      Swift version 6.2-dev (LLVM 53b6f8897dfb1be, Swift dd978623053f986)
2.      Compiling with effective version 5.10
3.      While evaluating request ASTLoweringRequest(Lowering AST to SIL for module main)
4.      While emitting reabstraction thunk in SIL function "@$sSdSgAAIegyd_SdAAIegyd_TR".
 for <<debugloc at "<compiler-generated>":0:0>>Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  swift-frontend           0x000000010accc224 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x000000010acca768 llvm::sys::RunSignalHandlers() + 112
2  swift-frontend           0x000000010accc868 SignalHandler(int) + 292
3  libsystem_platform.dylib 0x00000001810b4184 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018107ef70 pthread_kill + 288
5  libsystem_c.dylib        0x0000000180f8b908 abort + 128
6  swift-frontend           0x00000001029eee94 swift::DiagnosticHelper::Implementation::diagnoseFatalError(char const*, bool) + 668
7  swift-frontend           0x00000001029ef204 swift::DiagnosticHelper::diagnoseFatalError(char const*, bool) + 56
8  swift-frontend           0x000000010257a790 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*)::$_0::operator()(void*, char const*, bool) const + 64
9  swift-frontend           0x000000010257a744 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*)::$_0::__invoke(void*, char const*, bool) + 56
10 swift-frontend           0x000000010ac3352c llvm::report_fatal_error(llvm::Twine const&, bool) + 256
11 swift-frontend           0x000000010ac3342c llvm::report_fatal_error(llvm::Twine const&, bool) + 0
12 swift-frontend           0x00000001035b2b20 (anonymous namespace)::Transform::transform(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 2852
13 swift-frontend           0x00000001035b11f8 swift::Lowering::SILGenFunction::emitTransformedValue(swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 260
14 swift-frontend           0x00000001035c6aec (anonymous namespace)::TranslateArguments::processPrimitive(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::ManagedValue, swift::SILType, swift::Lowering::SGFContext) + 252
15 swift-frontend           0x00000001035c5380 (anonymous namespace)::TranslateArguments::processIntoOwned(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::ManagedValue, swift::SILType) + 212
16 swift-frontend           0x00000001035c43c8 (anonymous namespace)::TranslateArguments::processSingle(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::ManagedValue, (anonymous namespace)::ParamInfo) + 860
17 swift-frontend           0x00000001035c236c (anonymous namespace)::TranslateArguments::expandSingle(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType) + 244
18 swift-frontend           0x00000001035bf9b4 (anonymous namespace)::ExpanderBase<(anonymous namespace)::TranslateArguments, (anonymous namespace)::ParamInfo>::expand(swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType) + 1384
19 swift-frontend           0x00000001035cf0cc (anonymous namespace)::TranslateArguments::expandParam(swift::Lowering::AbstractionPattern, swift::AnyFunctionType::CanParam, swift::Lowering::AbstractionPattern, swift::AnyFunctionType::CanParam) + 484
20 swift-frontend           0x00000001035c06a8 (anonymous namespace)::TranslateArguments::expandOuterSingleInnerParam(swift::Lowering::AbstractionPattern, swift::AnyFunctionType::CanParam, swift::Lowering::FunctionInputGenerator&) + 196
21 swift-frontend           0x00000001035b4f1c (anonymous namespace)::TranslateArguments::process(swift::Lowering::AbstractionPattern, swift::ArrayRefView<swift::AnyFunctionType::Param, swift::AnyFunctionType::CanParam, swift::AnyFunctionType::CanParam::getFromParam(swift::AnyFunctionType::Param const&), true>, swift::Lowering::AbstractionPattern, swift::ArrayRefView<swift::AnyFunctionType::Param, swift::AnyFunctionType::CanParam, swift::AnyFunctionType::CanParam::getFromParam(swift::AnyFunctionType::Param const&), true>, bool) + 1276
22 swift-frontend           0x00000001035b88fc buildThunkBody(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::CanTypeWrapper<swift::SILFunctionType>, swift::CanType, llvm::function_ref<void (swift::Lowering::SILGenFunction&)>) + 1184
23 swift-frontend           0x00000001035bc8a4 createThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::TypeLowering const&) + 2040
24 swift-frontend           0x00000001035bd098 createDifferentiableFunctionThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>) + 716
25 swift-frontend           0x00000001035bc598 createThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::TypeLowering const&) + 1260
26 swift-frontend           0x00000001035ba87c (anonymous namespace)::Transform::transformFunction(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::TypeLowering const&) + 1168
27 swift-frontend           0x00000001035b25fc (anonymous namespace)::Transform::transform(swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 1536
28 swift-frontend           0x00000001035b11f8 swift::Lowering::SILGenFunction::emitTransformedValue(swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanType, swift::Lowering::AbstractionPattern, swift::CanType, swift::SILType, swift::Lowering::SGFContext) + 260
29 swift-frontend           0x00000001035b1f64 swift::Lowering::SILGenFunction::emitTransformedValue(swift::SILLocation, swift::Lowering::ManagedValue, swift::CanType, swift::CanType, swift::Lowering::SGFContext) + 256

[asl]

@hamishknight Actually, the thunk generation code is ok (and differentiable thunk generation just builds normal thunk and then applies some autodiff magic on top of that). The implicit conversion itself is broken:

                          (function_conversion_expr implicit type="@differentiable(reverse) (Double) -> Double?" location=opt2.swift:9:29 range=[opt2.swift:9:29 - line:9:29]
                            (differentiable_function implicit type="@differentiable(reverse) (Double) -> Double?" location=opt2.swift:9:29 range=[opt2.swift:9:29 - line:9:29]
                              (declref_expr type="(Double?) -> Double?" location=opt2.swift:9:29 range=[opt2.swift:9:29 - line:9:29] decl="opt2.(file).testFunc@opt2.swift:4:6" function_ref=unapplied))))))

Note that the type of differentiable_function node is @differentiable(reverse) (Double) -> Double?, so from thunk generation perspective we're converting (Double) -> Double? to (Double) -> Double? hence the assertion, it tries to convert Double argument to Double :)

Looks like the order is wrong: we need first do function_conversion_expr and then apply differentiable_function.

[hamishknight]

swift/lib/Sema/CSApply.cpp

Lines 7502 to 7503 in f1f1051

	fromFunc = FunctionType::get(toFunc->getParams(), fromFunc->getResult(),
	newEI);

Seems like toFunc->getParams() probably ought to be fromFunc->getParams() here? Still looks like it crashes though as lowering the FunctionConversionExpr for a differentiable function type gets pushed through createDifferentiableFunctionThunk too.

FunctionConversionExpr can normally handle these kinds of conversions though, e.g this is fine:

func testFunc(_ x: Double?) -> Double? { nil }
let fn: (Double) -> Double? = testFunc

(function_conversion_expr implicit type="(Double) -> Double?" location=/Users/hamish/src/swift-test-arena/main.swift:575:31 range=[/Users/hamish/src/swift-test-arena/main.swift:575:31 - line:575:31]
  (declref_expr type="(Double?) -> Double?" location=/Users/hamish/src/swift-test-arena/main.swift:575:31 range=[/Users/hamish/src/swift-test-arena/main.swift:575:31 - line:575:31] decl="main.(file).testFunc@/Users/hamish/src/swift-test-arena/main.swift:573:6" function_ref=unapplied)))))

Looks like the order is wrong: we need first do function_conversion_expr and then apply differentiable_function

That wouldn't help cases like this:

@differentiable(reverse)
func testFunc(_ x: Double?) -> Double? {}

let fn1: @differentiable(reverse) (Double?) -> Double? = testFunc
let fn2: @differentiable(reverse) (Double) -> Double? = fn1

For fn2, there's only a FunctionConversionExpr, but it still crashes since it goes through createDifferentiableFunctionThunk in SIL.

and differentiable thunk generation just builds normal thunk and then applies some autodiff magic on top of that

I think the extra magic is the issue here:

frame #24: 0x0000000101405ad8 swift-frontend`createDifferentiableFunctionThunk(swift::Lowering::SILGenFunction&, swift::SILLocation, swift::Lowering::ManagedValue, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>, swift::Lowering::AbstractionPattern, swift::CanTypeWrapper<swift::AnyFunctionType>)::$_1::operator()(this=0x000000016fdf1d90, kind=(rawValue = JVP)) const at SILGenPoly.cpp:5704:12
   5701	        loc, kind, borrowedFnValue.getValue());
   5702	    derivativeFn = SGF.B.emitCopyValueOperation(loc, derivativeFn);
   5703	    auto managedDerivativeFn = SGF.emitManagedRValueWithCleanup(derivativeFn);
-> 5704	    return createThunk(SGF, loc, managedDerivativeFn, derivativeFnInputOrigType,
    	           ^
   5705	                       derivativeFnInputSubstType, derivativeFnOutputOrigType,
   5706	                       derivativeFnOutputSubstType, derivativeFnExpectedTL);
   5707	  };
(lldb) p derivativeFnInputSubstType->dump()
(function_type escaping
  (input=function_params num_params=1
    (param 
      (bound_generic_enum_type decl="Swift.(file).Optional"
        (struct_type decl="Swift.(file).Double"))))
  (output=tuple_type num_elements=2
    (tuple_type_elt
      (bound_generic_enum_type decl="Swift.(file).Optional"
        (struct_type decl="Swift.(file).Double")))
    (tuple_type_elt
      (function_type escaping
        (input=function_params num_params=1
          (param 
            (struct_type decl="_Differentiation.(file).Optional extension.TangentVector"
              (parent=bound_generic_enum_type decl="Swift.(file).Optional"
                (struct_type decl="Swift.(file).Double")))))
        (output=struct_type decl="_Differentiation.(file).Optional extension.TangentVector"
          (parent=bound_generic_enum_type decl="Swift.(file).Optional"
            (struct_type decl="Swift.(file).Double")))))))
(lldb) p derivativeFnOutputSubstType->dump()
(function_type escaping
  (input=function_params num_params=1
    (param 
      (struct_type decl="Swift.(file).Double")))
  (output=tuple_type num_elements=2
    (tuple_type_elt
      (bound_generic_enum_type decl="Swift.(file).Optional"
        (struct_type decl="Swift.(file).Double")))
    (tuple_type_elt
      (function_type escaping
        (input=function_params num_params=1
          (param 
            (struct_type decl="Swift.(file).Double")))
        (output=struct_type decl="_Differentiation.(file).Optional extension.TangentVector"
          (parent=bound_generic_enum_type decl="Swift.(file).Optional"
            (struct_type decl="Swift.(file).Double")))))))

The input type should convert fine, but the output type is now also being changed from (Optional<Double>.TangentVector) -> Optional<Double>.TangentVector to (Double) -> Optional<Double>.TangentVector, which is what crashes.