[SR-15566] Differentiable functions with control flow yield an assertion failure: "location is a VarDecl, but SILDebugVariable is empty"

[BradLarson]

Previous ID	SR-15566
Radar	None
Original Reporter	@BradLarson
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, AutoDiff
Assignee	@rxwei
Priority	Medium

md5: cc857cf6edb138b26261ab8a61df5c82

Issue Description:

Starting with the 2021-12-04 nightly snapshot, certain differentiable functions that involve struct or local `var`s cause an assertion failure of "location is a VarDecl, but SILDebugVariable is empty". A simple reproducer is as follows:

import _Differentiation

public struct Test: Differentiable {
    public var v1: [[Float]]

    @differentiable(reverse)
    public init(v1: [[Float]]) {
        if v1.count != 2 {
            fatalError("Mismatched counts")
        }
        self.v1 = v1
    }
}

Place the above by itself in a file and build with swiftc file.swift to trigger this failure. The full assertion text is as follows:

Assertion failed: ((!dyn_cast_or_null<VarDecl>(Loc.getAsASTNode<Decl>()) || Var) && "location is a VarDecl, but SILDebugVariable is empty"), function createAllocStack, file SILBuilder.h, line 389.
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-2021-12-02-a.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file /Users/bradlarson/Development/DifferentiableSwift/CompilerBugs/VarDeclCrasher/VarDeclCrasher/main.swift -emit-dependencies-path /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/Objects-normal/x86_64/main.d -emit-reference-dependencies-path /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/Objects-normal/x86_64/main.swiftdeps -serialize-diagnostics-path /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/Objects-normal/x86_64/main.dia -target x86_64-apple-macos11.3 -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk -I /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Products/Debug -F /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Products/Debug -enable-testing -g -module-cache-path /Users/bradlarson/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -swift-version 5 -enforce-exclusivity=checked -Onone -D DEBUG -new-driver-path /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2021-12-02-a.xctoolchain/usr/bin/swift-driver -serialize-debugging-options -resource-dir /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2021-12-02-a.xctoolchain/usr/lib/swift -enable-anonymous-context-mangled-names -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/swift-overrides.hmap -Xcc -iquote -Xcc /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/VarDeclCrasher-generated-files.hmap -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/VarDeclCrasher-own-target-headers.hmap -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/VarDeclCrasher-all-target-headers.hmap -Xcc -iquote -Xcc /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/VarDeclCrasher-project-headers.hmap -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Products/Debug/include -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/DerivedSources-normal/x86_64 -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/DerivedSources/x86_64 -Xcc -I/Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/DerivedSources -Xcc -DDEBUG=1 -Xcc -working-directory/Users/bradlarson/Development/DifferentiableSwift/CompilerBugs/VarDeclCrasher -module-name VarDeclCrasher -target-sdk-version 11.3.0 -o /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Build/Intermediates.noindex/VarDeclCrasher.build/Debug/VarDeclCrasher.build/Objects-normal/x86_64/main.o -index-store-path /Users/bradlarson/Library/Developer/Xcode/DerivedData/VarDeclCrasher-ahvubcfxipupclheemrxtzypaszf/Index/DataStore -index-system-modules
1.  Apple Swift version 5.6-dev (LLVM 45a3cc180a9a385, Swift 8a7ca32cf0f903f)
2.  Compiling with the current language version
3.  While evaluating request ExecuteSILPipelineRequest(Run pipelines { Mandatory Diagnostic Passes + Enabling Optimization Passes } on SIL for VarDeclCrasher)
4.  While running pass #&#8203;142 SILModuleTransform "Differentiation".
5.  While processing // differentiability witness for Test.init(v1:)
sil_differentiability_witness [serialized] [reverse] [parameters 0] [results 0] @$s14VarDeclCrasher4TestV2v1ACSaySaySfGG_tcfC : $@convention(method) (@owned Array<Array<Float>>, @thin Test.Type) -> @owned Test {
}

 on SIL function "@$s14VarDeclCrasher4TestV2v1ACSaySaySfGG_tcfC".
 for 'init(v1:)' (at /Users/bradlarson/Development/DifferentiableSwift/CompilerBugs/VarDeclCrasher/VarDeclCrasher/main.swift:7:12)
6.  While generating VJP for SIL function "@$s14VarDeclCrasher4TestV2v1ACSaySaySfGG_tcfC".
 for 'init(v1:)' (at /Users/bradlarson/Development/DifferentiableSwift/CompilerBugs/VarDeclCrasher/VarDeclCrasher/main.swift:7:12)
7.  While generating pullback for SIL function "@$s14VarDeclCrasher4TestV2v1ACSaySaySfGG_tcfC".
 for 'init(v1:)' (at /Users/bradlarson/Development/DifferentiableSwift/CompilerBugs/VarDeclCrasher/VarDeclCrasher/main.swift:7:12)
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           0x000000010b058967 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 39
1  swift-frontend           0x000000010b057b85 llvm::sys::RunSignalHandlers() + 85
2  swift-frontend           0x000000010b058fa0 SignalHandler(int) + 288
3  libsystem_platform.dylib 0x00007fff20367d7d _sigtramp + 29
4  libsystem_platform.dylib 0x0000000000000089 _sigtramp + 18446603339975721769
5  libsystem_c.dylib        0x00007fff20277406 abort + 125
6  libsystem_c.dylib        0x00007fff202767d8 err + 0
7  swift-frontend           0x000000010b0bb493 swift::SILBuilder::createAllocStack(swift::SILLocation, swift::SILType, llvm::Optional<swift::SILDebugVariable>, bool, bool) (.cold.2) + 35
8  swift-frontend           0x000000010647c2c1 swift::SILBuilder::createAllocStack(swift::SILLocation, swift::SILType, llvm::Optional<swift::SILDebugVariable>, bool, bool) + 673
9  swift-frontend           0x0000000106aabe04 swift::autodiff::TangentBuilder::emitAdd(swift::SILLocation, swift::SILValue, swift::SILValue) + 468
10 swift-frontend           0x0000000106aa03f6 swift::autodiff::PullbackCloner::Implementation::accumulateAdjointsDirect(swift::autodiff::AdjointValue, swift::autodiff::AdjointValue, swift::SILLocation) + 438
11 swift-frontend           0x0000000106a99216 swift::autodiff::PullbackCloner::Implementation::addAdjointValue(swift::SILBasicBlock*, swift::SILValue, swift::autodiff::AdjointValue, swift::SILLocation) + 1286
12 swift-frontend           0x0000000106a9d607 swift::autodiff::PullbackCloner::Implementation::visit(swift::SILInstruction*) + 167
13 swift-frontend           0x0000000106a996bb swift::autodiff::PullbackCloner::Implementation::visitSILBasicBlock(swift::SILBasicBlock*) + 811
14 swift-frontend           0x0000000106a96aa7 swift::autodiff::PullbackCloner::Implementation::run() + 6967
15 swift-frontend           0x0000000106a94f42 swift::autodiff::PullbackCloner::run() + 18
16 swift-frontend           0x0000000106ab6308 swift::autodiff::VJPCloner::Implementation::run() + 1528
17 swift-frontend           0x0000000106ab69c2 swift::autodiff::VJPCloner::run() + 18
18 swift-frontend           0x0000000106bdc2b2 (anonymous namespace)::DifferentiationTransformer::canonicalizeDifferentiabilityWitness(swift::SILDifferentiabilityWitness*, swift::autodiff::DifferentiationInvoker, swift::IsSerialized_t) + 6882
19 swift-frontend           0x0000000106bd9dc8 (anonymous namespace)::Differentiation::run() + 1432
20 swift-frontend           0x0000000106c35581 swift::SILPassManager::runModulePass(unsigned int) + 689
21 swift-frontend           0x0000000106c3a57a swift::SILPassManager::execute() + 634
22 swift-frontend           0x0000000106c32168 swift::SILPassManager::executePassPipelinePlan(swift::SILPassPipelinePlan const&) + 72
23 swift-frontend           0x0000000106c320f1 swift::ExecuteSILPipelineRequest::evaluate(swift::Evaluator&, swift::SILPipelineExecutionDescriptor) const + 65
24 swift-frontend           0x0000000106c52c7d swift::SimpleRequest<swift::ExecuteSILPipelineRequest, std::__1::tuple<> (swift::SILPipelineExecutionDescriptor), (swift::RequestFlags)1>::evaluateRequest(swift::ExecuteSILPipelineRequest const&, swift::Evaluator&) + 29
25 swift-frontend           0x0000000106c3d121 llvm::Expected<swift::ExecuteSILPipelineRequest::OutputType> swift::Evaluator::getResultUncached<swift::ExecuteSILPipelineRequest>(swift::ExecuteSILPipelineRequest const&) + 241
26 swift-frontend           0x0000000106c323a2 swift::executePassPipelinePlan(swift::SILModule*, swift::SILPassPipelinePlan const&, bool, swift::irgen::IRGenModule*) + 82
27 swift-frontend           0x0000000106c401b7 swift::runSILDiagnosticPasses(swift::SILModule&) + 87
28 swift-frontend           0x00000001063f731c swift::CompilerInstance::performSILProcessing(swift::SILModule*) + 60
29 swift-frontend           0x00000001062955f1 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*) + 625
30 swift-frontend           0x0000000106294c15 performCompileStepsPostSema(swift::CompilerInstance&, int&, swift::FrontendObserver*) + 693
31 swift-frontend           0x000000010628a265 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3845
32 swift-frontend           0x000000010623c0a9 swift::mainEntry(int, char const**) + 553
33 libdyld.dylib            0x00007fff2033df3d start + 1
34 libdyld.dylib            0x0000000000000047 start + 18446603339975893259
error: Abort trap: 6 (in target 'VarDeclCrasher' from project 'VarDeclCrasher')

[rxwei]

Accidental fix #40503

[astrotuna201]

Unfortunately it seems this bug cropped up again in recent release (5.6, 2022-03-08) for the same tests as above:

% xcrun /Library/Developer/Toolchains/swift-5.6-RELEASE.xctoolchain/usr/bin/swift --version                

Apple Swift version 5.6 (swift-5.6-RELEASE)

Target: arm64-apple-macosx12.0

% xcrun /Library/Developer/Toolchains/swift-5.6-RELEASE.xctoolchain/usr/bin/swiftc crasher.swift -o crasher

error: compile command failed due to signal 6 (use -v to see invocation)

Assertion failed: ((!dyn_cast_or_null<VarDecl>(Loc.getAsASTNode<Decl>()) || Var) && "location is a VarDecl, but SILDebugVariable is empty"), function createAllocStack, file SILBuilder.h, line 389.

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-5.6-RELEASE.xctoolchain/usr/bin/swift-frontend -frontend -c -primary-file crasher.swift -target arm64-apple-macosx12.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -color-diagnostics -new-driver-path /Library/Developer/Toolchains/swift-5.6-RELEASE.xctoolchain/usr/bin/swift-driver -resource-dir /Library/Developer/Toolchains/swift-5.6-RELEASE.xctoolchain/usr/lib/swift -module-name crasher -target-sdk-version 12.3 -o /var/folders/hq/bm2zh17n5gq1xbhtvm30rj7r0000gn/T/TemporaryDirectory.XXxuRK/crasher-1.o

1. Apple Swift version 5.6 (swift-5.6-RELEASE)

2. Compiling with the current language version

3. While evaluating request ExecuteSILPipelineRequest(Run pipelines \{ Mandatory Diagnostic Passes + Enabling Optimization Passes } on SIL for crasher)

4. While running pass #&#8203;142 SILModuleTransform "Differentiation".

5. While processing // differentiability witness for Test.init(v1:)

sil_differentiability_witness [serialized] [reverse] [parameters 0] [results 0] @$s7crasher4TestV2v1ACSaySaySfGG_tcfC : $@convention(method) (@owned Array<Array<Float>>, @thin Test.Type) -> @owned Test {

}

 

 on SIL function "@$s7crasher4TestV2v1ACSaySaySfGG_tcfC".

 for 'init(v1:)' (at crasher.swift:7:12)

6. While generating VJP for SIL function "@$s7crasher4TestV2v1ACSaySaySfGG_tcfC".

 for 'init(v1:)' (at crasher.swift:7:12)

7. While generating pullback for SIL function "@$s7crasher4TestV2v1ACSaySaySfGG_tcfC".

 for 'init(v1:)' (at crasher.swift:7:12)

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           0x0000000106b3c9a4 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56

1  swift-frontend           0x0000000106b3bc04 llvm::sys::RunSignalHandlers() + 128

2  swift-frontend           0x0000000106b3d008 SignalHandler(int) + 304

3  libsystem_platform.dylib 0x000000019d5bd4c4 _sigtramp + 56

4  libsystem_pthread.dylib  0x000000019d5a5ee0 pthread_kill + 288

5  libsystem_c.dylib        0x000000019d4e0340 abort + 168

6  libsystem_c.dylib        0x000000019d4df754 err + 0

7  swift-frontend           0x0000000106b880e8 swift::SILCloner<(anonymous namespace)::TrivialCloner>::getOpType(swift::SILType) (.cold.1) + 0

8  swift-frontend           0x00000001029d8640 swift::SILBuilder::createAllocStack(swift::SILLocation, swift::SILType, llvm::Optional<swift::SILDebugVariable>, bool, bool) + 668

9  swift-frontend           0x0000000102f50ce8 swift::autodiff::TangentBuilder::emitAdd(swift::SILLocation, swift::SILValue, swift::SILValue) + 464

10 swift-frontend           0x0000000102f46cc4 swift::autodiff::PullbackCloner::Implementation::accumulateAdjointsDirect(swift::autodiff::AdjointValue, swift::autodiff::AdjointValue, swift::SILLocation) + 424

11 swift-frontend           0x0000000102f40b98 swift::autodiff::PullbackCloner::Implementation::addAdjointValue(swift::SILBasicBlock*, swift::SILValue, swift::autodiff::AdjointValue, swift::SILLocation) + 1172

12 swift-frontend           0x0000000102f4452c swift::autodiff::PullbackCloner::Implementation::visit(swift::SILInstruction*) + 200

13 swift-frontend           0x0000000102f40fbc swift::autodiff::PullbackCloner::Implementation::visitSILBasicBlock(swift::SILBasicBlock*) + 688

14 swift-frontend           0x0000000102f3e710 swift::autodiff::PullbackCloner::Implementation::run() + 5064

15 swift-frontend           0x0000000102f3d31c swift::autodiff::PullbackCloner::run() + 24

16 swift-frontend           0x0000000102f58ea8 swift::autodiff::VJPCloner::Implementation::run() + 1368

17 swift-frontend           0x0000000102f594c4 swift::autodiff::VJPCloner::run() + 24

18 swift-frontend           0x000000010304eeec (anonymous namespace)::DifferentiationTransformer::canonicalizeDifferentiabilityWitness(swift::SILDifferentiabilityWitness*, swift::autodiff::DifferentiationInvoker, swift::IsSerialized_t) + 5272

19 swift-frontend           0x000000010304d048 (anonymous namespace)::Differentiation::run() + 924

20 swift-frontend           0x00000001030a4eb4 swift::SILPassManager::runModulePass(unsigned int) + 632

21 swift-frontend           0x00000001030aa268 swift::SILPassManager::execute() + 628

22 swift-frontend           0x00000001030a1fe4 swift::SILPassManager::executePassPipelinePlan(swift::SILPassPipelinePlan const&) + 68

23 swift-frontend           0x00000001030a1f6c swift::ExecuteSILPipelineRequest::evaluate(swift::Evaluator&, swift::SILPipelineExecutionDescriptor) const + 68

24 swift-frontend           0x00000001030bfc40 swift::SimpleRequest<swift::ExecuteSILPipelineRequest, std::__1::tuple<> (swift::SILPipelineExecutionDescriptor), (swift::RequestFlags)1>::evaluateRequest(swift::ExecuteSILPipelineRequest const&, swift::Evaluator&) + 28

25 swift-frontend           0x00000001030ac544 llvm::Expected<swift::ExecuteSILPipelineRequest::OutputType> swift::Evaluator::getResultUncached<swift::ExecuteSILPipelineRequest>(swift::ExecuteSILPipelineRequest const&) + 252

26 swift-frontend           0x00000001030a21e0 swift::executePassPipelinePlan(swift::SILModule*, swift::SILPassPipelinePlan const&, bool, swift::irgen::IRGenModule*) + 84

27 swift-frontend           0x00000001030aebb4 swift::runSILDiagnosticPasses(swift::SILModule&) + 92

28 swift-frontend           0x0000000102967d34 swift::CompilerInstance::performSILProcessing(swift::SILModule*) + 68

29 swift-frontend           0x000000010282c608 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*) + 620

30 swift-frontend           0x000000010282be3c bool llvm::function_ref<bool (swift::CompilerInstance&)>::callback_fn<performAction(swift::CompilerInstance&, int&, swift::FrontendObserver*)::$_19>(long, swift::CompilerInstance&) + 572

31 swift-frontend           0x0000000102822a8c swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2960

32 swift-frontend           0x00000001027e1104 swift::mainEntry(int, char const**) + 524

33 dyld                     0x000000010f121088 start + 516