[SR-11450] Compiler crashes with 'Illegal instruction: 4' when running MergeSwiftModule

[swift-ci]

Previous ID	SR-11450
Radar	rdar://problem/55263077
Original Reporter	anlaital (JIRA User)
Type	Bug

Attachment: Download

Environment

Xcode 11 GM

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, 5.1Regression, CompilerCrash
Assignee	None
Priority	Medium

md5: 3eb76226bda89877306cdf3aee38468a

Issue Description:

This is a regression issue in Xcode 11 and caused by the compiler going into an infinite loop.

You can find the minimalistic repro case as an attachment. Compiling it will result in a crash with Xcode 11 GM.

[belkadan]

Thank you!

@swift-ci create

[typesanitizer]

Confirming that I'm able to reproduce the issue, including on master 656fe89 (Mon Sep 9). (Note to anyone else trying: use the .xcworkspace, not the .xcodeproj, so that the Pods.xcodeproj also gets compiled.)

[belkadan]

Looks like this is due to the circular dependency between these two types:

class FormPushCell: Cell<FormPushRow.FormPushRowObject>, CellType { }
final class FormPushRow: Row<FormPushCell>, RowType { … }

That code should be legal in Swift, but the serialization logic is trying to make sure that all of the types each class depends on can be deserialized before deserializing the class itself.

anlaital (JIRA User), you can work around this by moving FormPushRow.FormPushRowObject out to being a top-level struct with a typealias inside FormPushRow.