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Doug Gregor
376183f923
When a class conforms to a protocol, the witness thunk might have a covariant Self generic parameter. The presence of this generic parameter causes problems when the witness thunk calls a default implementation, because that default implementation is generic. To avoid this problem, inline the callee into the witness thunk so it becomes non-generic while retaining dynamic dispatch on the actual Self type. This is a longstanding issue with Embedded Swift and classes that conform to protocols. Fixes rdar://177527091.
48 lines
2.0 KiB
Swift
48 lines
2.0 KiB
Swift
// RUN: %target-swift-emit-sil %s -enable-experimental-feature Embedded -wmo -module-name main | %FileCheck %s
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// REQUIRES: swift_feature_Embedded
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// A non-final class that conforms to a protocol via a protocol-extension
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// default implementation gets a witness thunk that is generic over its
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// (class-constrained) conforming type -- the covariant-Self pattern,
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// `<τ : ConcreteClass>`. The default implementation is itself generic over
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// `<Self : Protocol>`, whose signature cannot be emitted in embedded Swift.
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//
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// The mandatory-performance-optimizations pass must inline that default impl
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// into the witness thunk so the thunk no longer references the un-emittable
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// generic callee. This test locks in that inlining (and guards against the
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// inliner failing to fire, or -- for a recursive default impl -- inlining
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// unboundedly and exhausting memory).
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public protocol Greeter {
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func greet() -> Int
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}
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extension Greeter {
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public func greet() -> Int { return 100 }
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}
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// Non-final class: its witness thunk is generic over `<τ : Animal>`.
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public class Animal: Greeter {}
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// A subclass exercises the covariant-Self aspect (the thunk really is generic,
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// not specialized to the exact class).
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public class Dog: Animal {}
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// Use the conformers through an existential so the witness table -- and thus
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// the generic witness thunk -- is live and reaches the optimizer/IRGen.
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@_silgen_name("run")
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public func run(_ g: any Greeter) -> Int {
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return g.greet()
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}
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// The witness thunk for Animal must have the default impl inlined: no
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// `function_ref`/`apply` of the generic default implementation remains, just
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// its folded-in body returning 100.
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// CHECK-LABEL: sil {{.*}}@$e4main6AnimalCAA7GreeterA2aDP5greetSiyFTW : $@convention(witness_method: Greeter) <τ_0_0 where τ_0_0 : Animal>
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// CHECK-NOT: function_ref @$e4main7GreeterPAAE5greetSiyF
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// CHECK-NOT: apply
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// CHECK: integer_literal $Builtin.Int{{[0-9]+}}, 100
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// CHECK: } // end sil function '$e4main6AnimalCAA7GreeterA2aDP5greetSiyFTW'
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