[SR-12589] Segmentation Fault when compiling instance method call from protocol

[swift-ci]

Previous ID	SR-12589
Radar	None
Original Reporter	ben-z (JIRA User)
Type	Bug
Status	Resolved
Resolution	Duplicate

Attachment: Download

Environment

> swift --version
Apple Swift version 5.2 (swiftlang-1103.0.32.1 clang-1103.0.32.29)
Target: x86_64-apple-darwin19.4.0

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: bee9a80b85986a4d2ed9df54dfaf1571

duplicates:

• SR-75 Referencing a protocol function crashes the compiler

Issue Description:

I'm getting a segmentation fault when I try to compile code that includes an instance call using protocol methods (not sure how to properly word this). Consider this example:
{{
import Foundation

protocol SomeProtocol {
func someMethod()
}

class SomeClass: SomeProtocol {
func someMethod() {
print("hello")
}
}

let a = SomeClass()
SomeProtocol.someMethod(a)()
}}

Compiling this results in a segfault:

```
0. Program arguments: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -interpret test.swift -enable-objc-interop -stack-check -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -color-diagnostics -module-name test

1. Apple Swift version 5.2 (swiftlang-1103.0.32.1 clang-1103.0.32.29)
   0 swift 0x000000010f6e54ea PrintStackTraceSignalHandler(void*) + 42
   1 swift 0x000000010f6e4cc0 SignalHandler(int) + 352
   2 libsystem_platform.dylib 0x00007fff6ba155fd _sigtramp + 29
   3 libsystem_platform.dylib 0x0000000000800000 _sigtramp + 2497620512
   4 swift 0x000000010b8cea8a swift::Lowering::SILGenFunction::emitOpenExistentialExprImpl(swift::OpenExistentialExpr*, llvm::function_ref<void (swift::Expr*)>) + 666
   5 swift 0x000000010b8bfc2a swift::ASTVisitor<(anonymous namespace)::RValueEmitter, swift::Lowering::RValue, void, void, void, void, void, swift::Lowering::SGFContext>::visit(swift::Expr*, swift::Lowering::SGFContext) + 38938
   6 swift 0x000000010b86df63 (anonymous namespace)::SILGenApply::visitExpr(swift::Expr*) + 51
   7 swift 0x000000010b863304 swift::Lowering::SILGenFunction::emitApplyExpr(swift::ApplyExpr*, swift::Lowering::SGFContext) + 196
   8 swift 0x000000010b8d0297 swift::Lowering::SILGenFunction::emitIgnoredExpr(swift::Expr*) + 823
   9 swift 0x000000010b856a5b swift::ASTVisitor<swift::Lowering::SILGenModule, void, void, void, void, void, void>::visit(swift::Decl*) + 1227
   10 swift 0x000000010b8557ac swift::Lowering::SILGenModule::emitSourceFile(swift::SourceFile*) + 1356
   11 swift 0x000000010b85788a swift::SILModule::constructSIL(swift::ModuleDecl*, swift::Lowering::TypeConverter&, swift::SILOptions&, swift::FileUnit*) + 1530
   12 swift 0x000000010b4393cb swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 55595
   13 swift 0x000000010b3af4d3 main + 1283
   14 libdyld.dylib 0x00007fff6b81ccc9 start + 1
   15 libdyld.dylib 0x000000000000000b start + 2491298627
   [1] 13168 segmentation fault swift test.swift
   ```

[swift-ci]

Comment by Ben Zhang (JIRA)

Just realized that the segfault happens even without the call:

```
import Foundation

protocol SomeProtocol {
func someMethod()
}

let _ = SomeProtocol.someMethod
```

Is this intended (unsupported) behaviour?

[hamishknight]

This has been fixed on master by #28698 please verify using the latest development snapshot from https://swift.org/download/#snapshots.