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Void-returning @differentiable function crashes compiler #62923

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hamishknight opened this issue Jan 9, 2023 · 3 comments · Fixed by #63080
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Void-returning @differentiable function crashes compiler #62923

hamishknight opened this issue Jan 9, 2023 · 3 comments · Fixed by #63080
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@asl
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AutoDiff bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler itself crash Bug: A crash, i.e., an abnormal termination of software SILGen Area → compiler: The SIL generation stage swift 5.8 type checker Area → compiler: Semantic analysis

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@hamishknight
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The following crashes in SILGen:

import _Differentiation

func foo(_ fn: @differentiable(reverse) (Float) -> Void) {}
@hamishknight hamishknight added bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. AutoDiff labels Jan 9, 2023
@LucianoPAlmeida LucianoPAlmeida added compiler The Swift compiler itself compiler crash SILGen Area → compiler: The SIL generation stage labels Jan 9, 2023
@asl asl self-assigned this Jan 12, 2023
@asl
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asl commented Jan 18, 2023

So, the reason here is Void (aka empty tuple) type is assumed to be differentiable with tangent space being empty tuple as well.

Looks like we'd need to additionally check and disallow void result type if there are no inouts.

Tagging @rxwei @dan-zheng @BradLarson

@rxwei
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rxwei commented Jan 18, 2023

Yeah that sounds about right. @asl

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asl commented Jan 18, 2023

@rxwei Thanks for cross-checking! It tried to imagine other corner cases related to Void but failed to find any so far :)

@asl asl mentioned this issue Jan 18, 2023
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asl added a commit to asl/swift that referenced this issue Jan 18, 2023
@asl
Diagnose differentiable functions returning Void w/o inout arguments.
5c993eb 
Such functions are not differentiable and therefore should be rejected.
Fixes swiftlang#62923
asl added a commit that referenced this issue Jan 18, 2023
@asl
Diagnose differentiable functions returning Void w/o inout arguments. (…
0763e4b 
…#63080)

Such functions are not differentiable and therefore should be rejected.
Fixes #62923,  fixes #58095
@AnthonyLatsis AnthonyLatsis added type checker Area → compiler: Semantic analysis swift 5.8 crash Bug: A crash, i.e., an abnormal termination of software and removed compiler crash labels Apr 17, 2023
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@asl asl

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AutoDiff bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler itself crash Bug: A crash, i.e., an abnormal termination of software SILGen Area → compiler: The SIL generation stage swift 5.8 type checker Area → compiler: Semantic analysis
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Diagnose differentiable functions returning Void w/o inout arguments. asl/swift
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@asl @rxwei @LucianoPAlmeida @hamishknight @AnthonyLatsis