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[SR-9524] Optional flatMap produces differing results between debug and release build in special scenario. #51975

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swift-ci opened this issue Dec 15, 2018 · 1 comment
Open

[SR-9524] Optional flatMap produces differing results between debug and release build in special scenario. #51975

swift-ci opened this issue Dec 15, 2018 · 1 comment
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself optimized only Flag: An issue whose reproduction requires optimized compilation

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@swift-ci
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Previous ID SR-9524
Radar None
Original Reporter derekblr (JIRA User)
Type Bug

Attachment: Download

Environment

Xcode Version 10.1 (10B61)

Swift 4.2

iPhone 8 Simulator (12.1)

OSX 10.13.6 (17G3025)

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

md5: ef7b19558e2ff6cabbb02a9c8210debe

Issue Description:

I've attached a demo project to illustrate the behaviour.

This is what is happening. Consider the following code:

private func foo<T>() -> T? {
    return Optional<Any>.some(Optional<Any>.none as Any) as? T
}


let test: Any? = foo().flatMap { $0 }
if test != nil {
    print("This happens in release")
} else {
    print("This happens in debug")
}

The test variable seems to be nil in debug builds and non-nil in release builds.
@belkadan
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cc @jckarter, @eeckstein. Sounds like the specializer + cast optimizer and the runtime don't agree?

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself optimized only Flag: An issue whose reproduction requires optimized compilation
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@belkadan @swift-ci