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[SR-6478] [SE-0143] IRGen Crash with conditional conformance of generic struct #49028

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DougGregor opened this issue Nov 27, 2017 · 7 comments
Open

[SR-6478] [SE-0143] IRGen Crash with conditional conformance of generic struct #49028

DougGregor opened this issue Nov 27, 2017 · 7 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself crash Bug: A crash, i.e., an abnormal termination of software

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@DougGregor
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Previous ID SR-6478
Radar None
Original Reporter @DougGregor
Type Bug

Attachment: Download

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, CompilerCrash
Assignee None
Priority Medium

md5: f3eea6684af9f3a682ffbda319003a4d

Issue Description:

The following crashes in IR generation when emitting the witness table for the conditional conformance `MySlice: BidirectionalCollection`:

Assertion failed: (result && "get() on unmapped entry?"), function get, file /Users/dgregor/Projects/swift/swift/lib/IRGen/LocalTypeData.h, line 231.
0  swift                    0x00000001104e9408 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
1  swift                    0x00000001104e8356 llvm::sys::RunSignalHandlers() + 86
2  swift                    0x00000001104e99ce SignalHandler(int) + 366
3  libsystem_platform.dylib 0x00007fff61cf5f5a _sigtramp + 26
4  libsystem_platform.dylib 0x0000000000000001 _sigtramp + 2653987009
5  libsystem_c.dylib        0x00007fff61b2130a abort + 127
6  libsystem_c.dylib        0x00007fff61ae9360 basename_r + 0
7  swift                    0x000000010d239152 swift::irgen::IRGenFunction::getLocalTypeData(swift::CanType, swift::irgen::LocalTypeDataKind) + 114
8  swift                    0x000000010d0dc5d5 swift::irgen::emitArchetypeWitnessTableRef(swift::irgen::IRGenFunction&, swift::CanTypeWrapper<swift::ArchetypeType>, swift::ProtocolDecl*) + 725
9  swift                    0x000000010d0dc291 swift::irgen::emitAssociatedTypeMetadataRef(swift::irgen::IRGenFunction&, swift::CanTypeWrapper<swift::ArchetypeType>, swift::AssociatedType) + 97
10 swift                    0x000000010d0dc178 swift::irgen::emitArchetypeTypeMetadataRef(swift::irgen::IRGenFunction&, swift::CanTypeWrapper<swift::ArchetypeType>) + 104
11 swift                    0x000000010d1ae6c1 swift::SILWitnessVisitor<(anonymous namespace)::WitnessTableBuilder>::visitProtocolDecl(swift::ProtocolDecl*)::'lambda'()::operator()() const + 1089
12 swift                    0x000000010d1ad173 swift::SILWitnessVisitor<(anonymous namespace)::WitnessTableBuilder>::visitProtocolDecl(swift::ProtocolDecl*) + 835
13 swift                    0x000000010d1a5877 swift::irgen::IRGenModule::emitSILWitnessTable(swift::SILWitnessTable*) + 839
@DougGregor
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@slavapestov or @rjmccall, I may ask for your help in understanding how IRGen is supposed to work for these.

@DougGregor
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Significantly reduced so we no longer need the standard library:

protocol P {
  associatedtype A: P 
}

protocol Q: P where A: Q {
}

struct Wrapper<T: P>: P {
  typealias A = Wrapper<T>
}

extension Wrapper: Q where T: Q { }

@DougGregor
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The attached hack-patch works around a substitution issue where we don't have the contextual types we need. It get us to an assertion where, in the process of emitting the witness table `Wrapper<T>: Q`, we emit the witness table access function for `Self.A: Q`, which in this case is also `Wrapper<T>: Q`. We fail in `emitConditionalConformancesBuffer()`, because we're trying to fill in the (abstract) conformance of `T: Q`... which isn't a known fulfillment.

@rjmccall
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The extra thing that's done for conditional conformances in EmitPolymorphicParameters::bindExtraSources also needs to be done in the conformance's access functions.

@rjmccall
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We should also do the obvious optimization of adding the self conformance as unscoped local type data; if you do that, you'll need to change the test case to make A a slightly different type that still requires T: Q.

Make sure you do this in the type-metadata access function, too, for which the test case would be an associated type with an unconditional conformance requirement.

@DougGregor
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#13089

@DougGregor
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Merged that PR to get us further, but I'm deeply troubled by the first commit in there. I'm going to hold this bug open until I find a more palatable solution.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@AnthonyLatsis AnthonyLatsis added the crash Bug: A crash, i.e., an abnormal termination of software label Dec 12, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself crash Bug: A crash, i.e., an abnormal termination of software
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@rjmccall @DougGregor @AnthonyLatsis