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Ensure we are adding T : Differentiable conformance from protocol conditional conformance #77446

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Ensure we are adding T : Differentiable conformance from protocol conditional conformance #77446

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8 changes: 8 additions & 0 deletions lib/SILGen/SILGenPoly.cpp
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Expand Up @@ -7043,6 +7043,14 @@ void SILGenFunction::emitProtocolWitness(
FullExpr scope(Cleanups, cleanupLoc);
FormalEvaluationScope formalEvalScope(*this);

// The protocol conditional conformance itself might bring some T :
// Differentiable conformances. They are already added to the derivative
// generic signature. Update witness substitution map generic signature to
// have them as well.
if (auto *derivativeId = witness.getDerivativeFunctionIdentifier())
witnessSubs = SubstitutionMap::get(derivativeId->getDerivativeGenericSignature(),
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Should the correct witnessSubs be computed in Sema? See lib/AST/RequirementEnvironment.cpp

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@asl asl Nov 8, 2024 •
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It seems to be calculated correctly there:
<τ_0_0 where τ_0_0 : Differentiable> is a witness generic thunk signature and the corresponding requirement-to-witness substitution map is:

(substitution_map generic_signature=<Self where Self : P>
  (substitution Self ->
    (bound_generic_struct_type decl="main.(file)[email protected]:3:8"
      (generic_type_param_type depth=0 index=0 param_kind=type)))
  (conformance type="Self"
    (normal_conformance type="Wrapper<T>" protocol="P"
      (assoc_type req="T" type="T")
      (assoc_conformance type="Self" proto="Copyable"
        (builtin_conformance type="Wrapper<T>" protocol="Copyable"))
      (assoc_conformance type="Self" proto="Escapable"
        (builtin_conformance type="Wrapper<T>" protocol="Escapable"))
      (assoc_conformance type="Self.T" proto="Differentiable"
        (abstract_conformance protocol="Differentiable"))
      (requirement "T" conforms_to "Differentiable"))))

However, witnessSubs here is:

(substitution_map generic_signature=<T where T : Copyable, T : Escapable>
  (substitution T ->
    (primary_archetype_type address=0x15c9d8c18 conforms_to="_Differentiation.(file).Differentiable" name="\xCF\x84_0_0"
      (interface_type=generic_type_param_type depth=0 index=0 param_kind=type)))
  (conformance type="T"
    (abstract_conformance protocol="Copyable"))
  (conformance type="T"
    (abstract_conformance protocol="Escapable")))

So T : Differentiable comes from conditional conformance via substitution and is not part of generic signature.

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@slavapestov So, what do you think about this? Should we change the calculation somehow? For now I just made it conditional for autodiff and only adding T : Differentiable requirement. W/o this we are unable to calculate derivative function type in protocol conformance as we need to have corresponding associated types etc.

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@slavapestov Any further suggestions here?

witnessSubs);

auto thunkTy = F.getLoweredFunctionType();

SmallVector<ManagedValue, 8> origParams;
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26 changes: 26 additions & 0 deletions lib/Sema/TypeCheckProtocol.cpp
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Expand Up @@ -294,6 +294,29 @@ static ValueDecl *getStandinForAccessor(AbstractStorageDecl *witness,
return witness;
}

static GenericSignature maybeAddDifferentiableFromContext(DeclContext *dc,
GenericSignature derivativeGenSig) {
auto conformanceGenSig = dc->getGenericSignatureOfContext();
if (!conformanceGenSig)
return derivativeGenSig;

// The protocol conditional conformance itself might bring some T :
// Differentiable conformances. Add them the the derivative generic signature.
SmallVector<Requirement, 4> diffRequirements;
llvm::copy_if(conformanceGenSig.getRequirements(),
std::back_inserter(diffRequirements),
[](const Requirement &requirement) {
if (requirement.getKind() != RequirementKind::Conformance)
return false;

auto protoKind = requirement.getProtocolDecl()->getKnownProtocolKind();
return protoKind && *protoKind == KnownProtocolKind::Differentiable;
});

return buildGenericSignature(dc->getASTContext(), derivativeGenSig,
{}, std::move(diffRequirements), /*allowInverses=*/true);
}

/// Given a witness, a requirement, and an existing `RequirementMatch` result,
/// check if the requirement's `@differentiable` attributes are met by the
/// witness.
Expand Down Expand Up @@ -425,6 +448,9 @@ matchWitnessDifferentiableAttr(DeclContext *dc, ValueDecl *req,
auto derivativeGenSig = witnessAFD->getGenericSignature();
if (supersetConfig)
derivativeGenSig = supersetConfig->derivativeGenericSignature;

derivativeGenSig = maybeAddDifferentiableFromContext(dc, derivativeGenSig);

// Use source location of the witness declaration as the source location
// of the implicit `@differentiable` attribute.
auto *newAttr = DifferentiableAttr::create(
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22 changes: 22 additions & 0 deletions ...AutoDiff/compiler_crashers_fixed/issue-75711-conditional-differentiable-conformance.swift
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@@ -0,0 +1,22 @@
// RUN: %target-swift-frontend -emit-sil -verify %s

// https://github.com/swiftlang/swift/issues/75711

// Ensure we propagate T : Differentiable conditional conformance

import _Differentiation

struct Wrapper<T> {
func read(_ t: T) -> T {
return t
}
}

protocol P {
associatedtype T: Differentiable

@differentiable(reverse)
func read(_: T) -> T
}

extension Wrapper: P where T: Differentiable {}