@_silgen_name("foo")
func foo1<T>(_ x: T) {}

@_silgen_name("foo")
func foo2() {
  foo1(1)
}

$ swiftc crash.swift
Assertion failed: (fn->getLoweredFunctionType() == constantType), function getOrCreateFunction, file swift/lib/SIL/IR/SILFunctionBuilder.cpp, line 141.
Stack dump:
0.  Program arguments: build/Ninja-ReleaseAssert/swift-macosx-x86_64/bin/swift-frontend -frontend -c -primary-file crash.swift -target x86_64-apple-darwin19.4.0 -enable-objc-interop -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -color-diagnostics -target-sdk-version 10.16 -module-name crash -o /var/folders/m_/6f7q8zfs3n9fr0c_4gy8840m00hc_q/T/crash-737263.o
1.  Swift version 5.3-dev (LLVM 03a20a7d045e034, Swift 643aa2d8961c2f8)
2.  While evaluating request ASTLoweringRequest(Lowering AST to SIL for file "crash.swift")
0  swift-frontend           0x0000000107057815 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 37
1  swift-frontend           0x00000001070567e8 llvm::sys::RunSignalHandlers() + 248
2  swift-frontend           0x0000000107057df6 SignalHandler(int) + 262
3  libsystem_platform.dylib 0x00007fff6f73d5fd _sigtramp + 29
4  libsystem_platform.dylib 000000000000000000 _sigtramp + 18446603338646301216
5  libsystem_c.dylib        0x00007fff6f613808 abort + 120
6  libsystem_c.dylib        0x00007fff6f612ac6 err + 0
7  swift-frontend           0x00000001073a8a33 swift::SILFunctionBuilder::getOrCreateFunction(swift::SILLocation, swift::SILDeclRef, swift::ForDefinition_t, llvm::function_ref<swift::SILFunction* (swift::SILLocation, swift::SILDeclRef)>, swift::ProfileCounter) (.cold.4) + 35
8  swift-frontend           0x000000010358ce6c swift::SILFunctionBuilder::getOrCreateFunction(swift::SILLocation, swift::SILDeclRef, swift::ForDefinition_t, llvm::function_ref<swift::SILFunction* (swift::SILLocation, swift::SILDeclRef)>, swift::ProfileCounter) + 1676
9  swift-frontend           0x0000000102eef7bf swift::Lowering::SILGenModule::getFunction(swift::SILDeclRef, swift::ForDefinition_t) + 399