Type reconstruction fails for some @differentiable functions when unit tests are built for Profiling.

[fibrechannelscsi]

Description
The compiler crashes with an error message indicating that it failed to reconstruct the type for what appears to be a differentiable function, in the case of the below code.

Steps to reproduce

1. Use the code below in order to generate a library.

import _Differentiation
public struct F<I: Equatable, D> {public init() {}}
extension F: Equatable where D: Equatable {}
extension F: Differentiable where D: Differentiable, D.TangentVector == D {}
extension F: AdditiveArithmetic where D: AdditiveArithmetic {
    public static func + (lhs: F<I, D>, rhs: F<I, D>) -> F<I, D> {return lhs}
    public static func - (lhs: F<I, D>, rhs: F<I, D>) -> F<I, D> {return lhs}
    public static var zero: F<I, D> {return F<I, D>()}
}
public extension F where D: Differentiable, D == D.TangentVector {
    mutating func assign1(_ series: S<I, D>, at key: String?) {fatalError()}
    @differentiable(reverse)
    mutating func assign0(_ series: S<I, D>) {self.assign1(series, at: nil)}
    @inlinable
    @differentiable(reverse)
    mutating func assignMain(_ series: S<I, D>) {self.assign0(series)}
    @derivative(of: assign0)
    mutating func vjpAssign_(series: S<I, D>) -> (value: Void, pullback: (inout Self.TangentVector) -> S<I, D>.TangentVector)
    {
        return ((), {_ in S<I, D>.TangentVector.zero})
    }
//    @derivative(of: assignMain)
//    mutating func vjpAssignMain(series: S<I, D>) -> (value: Void, pullback: (inout Self.TangentVector) -> S<I, D>.TangentVector)
//    {
//        return ((), {_ in S<I, D>.TangentVector.zero})
//    }
    
}
public struct S<I, D> {public init(){}}
extension S: Equatable where D: Equatable {
    public static func == (lhs: S<I, D>, rhs: S<I, D>) -> Bool {fatalError()}
}
extension S: Differentiable where D: Differentiable, D.TangentVector == D{public typealias TangentVector = S<I, D>}
extension S: AdditiveArithmetic where D: AdditiveArithmetic {
    public static func + (_ lhs: Self, _ rhs: Self) -> Self {fatalError()}
    public static func - (_ lhs: Self, _ rhs: Self) -> Self {fatalError()}
    public static var zero: Self {fatalError()}
}

2. Specify the library generated by the code above as one of the imports to the unit test code below:

import _Differentiation
import PlayGround //Specify custom library name here.
import XCTest
class UnitTests: XCTestCase {
    func testA(){
        @differentiable(reverse)
        func a(input: S<Double, Double>) -> F<Double, Double> {
            var f = F<Double, Double>()
            f.assignMain(input)
            return f
        }
    }
}

3. In Xcode, right click and select Profile "testA()".

The compiler will generate an error that looks like:

Failed to reconstruct type for $s10PlayGround09_AD__$s10a131Ground1FVAA16_Differentiation14DifferentiableR_13TangentVectorAdEPQy_Rs_rlE10assignMainyyAA1SVyxq_GF_bb0__PB__src_0_wrt_0_1_SQRz16_gh4R_13ij7AaBPQy_M5_r0_lVyS2dGD
Original type:
(bound_generic_struct_type decl=PlayGround.(file)._AD__$s10PlayGround1FVAA16_Differentiation14DifferentiableR_13TangentVectorAdEPQy_Rs_rlE10assignMainyyAA1SVyxq_GF_bb0__PB__src_0_wrt_0_1_SQRz16_Differentiation14DifferentiableR_13TangentVectorAaBPQy_Rs_r0_l
  (struct_type decl=Swift.(file).Double)
  (struct_type decl=Swift.(file).Double))

Additional stack information:

1.	Apple Swift version 5.9-dev (LLVM c48958355f7507c, Swift f26f810cc8406ef)
2.	Compiling with the current language version
3.	While emitting IR SIL function "@$s10PlayGround1FVAA16_Differentiation14DifferentiableR_13TangentVectorAdEPQy_Rs_rlE10assignMainyyAA1SVyxq_GFSQRzAdER_AHRs_r0_lTJpSSpSrSd_SdTg5".
 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           0x000000010948d5c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1  swift-frontend           0x000000010948c84c llvm::sys::RunSignalHandlers() + 128
2  swift-frontend           0x000000010948dc08 SignalHandler(int) + 304
3  libsystem_platform.dylib 0x000000018d1314c4 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018d119ee0 pthread_kill + 288
5  libsystem_c.dylib        0x000000018d054340 abort + 168
6  swift-frontend           0x0000000109527c6c (anonymous namespace)::IRGenDebugInfoImpl::getOrCreateType(swift::irgen::DebugTypeInfo) (.cold.8) + 0
7  swift-frontend           0x0000000104f972f0 (anonymous namespace)::IRGenDebugInfoImpl::getOrCreateType(swift::irgen::DebugTypeInfo) + 3436
8  swift-frontend           0x0000000104f97aac (anonymous namespace)::IRGenDebugInfoImpl::createParameterType(llvm::SmallVectorImpl<llvm::Metadata*>&, swift::SILType) + 132
9  swift-frontend           0x0000000104f977c0 (anonymous namespace)::IRGenDebugInfoImpl::createParameterTypes(swift::CanTypeWrapper<swift::SILFunctionType>) + 404
10 swift-frontend           0x0000000104f90f3c (anonymous namespace)::IRGenDebugInfoImpl::emitFunction(swift::SILDebugScope const*, llvm::Function*, swift::SILFunctionTypeRepresentation, swift::SILType, swift::DeclContext*, llvm::StringRef) + 1720
11 swift-frontend           0x0000000104f917e8 (anonymous namespace)::IRGenDebugInfoImpl::emitFunction(swift::SILFunction&, llvm::Function*) + 160
12 swift-frontend           0x0000000104fcabdc (anonymous namespace)::IRGenSILFunction::emitSILFunction() + 880
13 swift-frontend           0x0000000104fca338 swift::irgen::IRGenModule::emitSILFunction(swift::SILFunction*) + 920
14 swift-frontend           0x0000000104e849a8 swift::irgen::IRGenerator::emitLazyDefinitions() + 1400
15 swift-frontend           0x0000000104f7bcc4 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**) + 1524
16 swift-frontend           0x0000000104bb2518 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*) + 1608
17 swift-frontend           0x0000000104bb1b38 swift::performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 1100
18 swift-frontend           0x0000000104bc063c withSemanticAnalysis(swift::CompilerInstance&, swift::FrontendObserver*, llvm::function_ref<bool (swift::CompilerInstance&)>, bool) + 160
19 swift-frontend           0x0000000104bb361c swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3204
20 swift-frontend           0x0000000104a09414 swift::mainEntry(int, char const**) + 3304
21 dyld                     0x00000001122e5088 start + 516

Expected behavior
The test should run successfully. Although many functions and computed properties are denoted as fatalError(), none of these are executed since the function a is not actually called. Namely, the type information should be able to be reconstructed without error.

Environment

• Swift compiler version info: 2023-01-19a. Fails with versions as far back as 2022-07-15a. The type reconstruction succeeds on 2022-05-23a, however.
• Xcode version info: 13.3 (13E113)
• Deployment target: iOS 12.3.1, ARM64.

Additional context
If the 5 lines in code block 1 are uncommented, then building testA for profiling succeeds. Namely, manual specification of @derivative(of: assignMain) causes the build to succeed.

[BradLarson]

cc @asl, this is possibly a recurrence of a similar earlier issue that we thought might have been masked instead of solved.

[asl]

Ok, steps to reproduce w/o XCode:

1. Save first file to playground.swift
2. Build module: swiftc playground.swift -emit-module -module-name PlayGround -emit-module-path playground/PlayGround.swiftmodule -DM
3. Compile testcase (actually XCTest is not needed): swiftc playground-test.swift -I playground -g -O

[asl]

Ok, something does not look good fundamentally.

What is going one:

1. The swift module exports functions along with their pullbacks, etc.
2. Pullback got specialized and debug info is requested for all newly-created stuff including reverse derivative
3. In particular, debug info is requested for linear map struct (_AD__$s10PlayGround1FVAA16_Differentiation14DifferentiableR_13TangentVectorAdEPQy_Rs_rlE10assignMainyyAA1SVyxq_GF_bb0__PB__src_0_wrt_0_1_SQRz16_Differentiation14D ifferentiableR_13TangentVectorAaBPQy_Rs_r0_l), however this struct is not exported. Struct, like many other aux types, is synthesized by compiler and added to artificial FileUnit. While everything works "locally", certainly nothing is exposed from the module (actually for the same reason SIL with autodiff code cannot be read back, as type declarations are missed for all _AD__* types).

@rxwei @dan-zheng , What was the reason they are not added as ordinary top-level decls to the main module?

[rxwei]

They are not written by the user so they are not added to the main source file. It's similar to macro expansions.

@DougGregor what's your take on this, given that you've recently dealt with macro expansion file units?