[AutoDiff] Underscore the Differentiable protocol.

include/swift/AST/KnownProtocols.def

@@ -85,14 +85,16 @@ PROTOCOL(KeyPathIterable)
 PROTOCOL(TensorArrayProtocol)
 PROTOCOL(TensorGroup)
 PROTOCOL(VectorProtocol)
-PROTOCOL(Differentiable)
 PROTOCOL(EuclideanDifferentiable)
+PROTOCOL(Expression)
 
 PROTOCOL_(ObjectiveCBridgeable)
 PROTOCOL_(DestructorSafeContainer)
 
 PROTOCOL(StringInterpolationProtocol)
 
+PROTOCOL_(Differentiable)
+
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByArrayLiteral, "Array", false)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByBooleanLiteral, "BooleanLiteralType", true)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByDictionaryLiteral, "Dictionary", false)
@@ -107,9 +109,9 @@ EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByUnicodeScalarLiteral, "UnicodeScala
 EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByColorLiteral, "_ColorLiteralType", true)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByImageLiteral, "_ImageLiteralType", true)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByFileReferenceLiteral, "_FileReferenceLiteralType", true)
+// SWIFT_ENABLE_TENSORFLOW
 // TODO(TF-735): Implement ExpressibleByQuoteLiteral.
 // EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByQuoteLiteral, "_QuoteLiteralType", true)
-PROTOCOL(Expression)
 
 BUILTIN_EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByBuiltinBooleanLiteral)
 BUILTIN_EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByBuiltinExtendedGraphemeClusterLiteral)

lib/AST/Builtins.cpp

@@ -1007,11 +1007,8 @@ static ValueDecl *getAutoDiffApplyAssociatedFunction(
   //       rethrows -> (R, (R.TangentVector) -> ...T.TangentVector)
   unsigned numGenericParams = 1 + arity;
   BuiltinGenericSignatureBuilder builder(Context, numGenericParams);
-  // Look up the Differentiable protocol.
-  SmallVector<ValueDecl *, 1> diffableProtoLookup;
-  Context.lookupInSwiftModule("Differentiable", diffableProtoLookup);
-  assert(diffableProtoLookup.size() == 1);
-  auto *diffableProto = cast<ProtocolDecl>(diffableProtoLookup.front());
+  // Get the `Differentiable` protocol.
+  auto *diffableProto = Context.getProtocol(KnownProtocolKind::Differentiable);
   // Create type parameters and add conformance constraints.
   auto fnResultGen = makeGenericParam(arity);
   builder.addConformanceRequirement(fnResultGen, diffableProto);

lib/IRGen/GenMeta.cpp

@@ -4216,7 +4216,7 @@ SpecialProtocol irgen::getSpecialProtocolID(ProtocolDecl *P) {
   case KnownProtocolKind::Encodable:
   case KnownProtocolKind::Decodable:
   case KnownProtocolKind::StringInterpolationProtocol:
-  case KnownProtocolKind::Expression:
+  case KnownProtocolKind::Differentiable:
   // SWIFT_ENABLE_TENSORFLOW
   case KnownProtocolKind::AdditiveArithmetic:
   case KnownProtocolKind::PointwiseMultiplicative:
@@ -4225,8 +4225,8 @@ SpecialProtocol irgen::getSpecialProtocolID(ProtocolDecl *P) {
   case KnownProtocolKind::TensorArrayProtocol:
   case KnownProtocolKind::TensorGroup:
   case KnownProtocolKind::VectorProtocol:
-  case KnownProtocolKind::Differentiable:
   case KnownProtocolKind::EuclideanDifferentiable:
+  case KnownProtocolKind::Expression:
     return SpecialProtocol::None;
   }
 

stdlib/public/core/CMakeLists.txt

@@ -30,8 +30,6 @@ set(SWIFTLIB_ESSENTIAL
   ASCII.swift
   Assert.swift
   AssertCommon.swift
-  # SWIFT_ENABLE_TENSORFLOW
-  AutoDiff.swift
   BidirectionalCollection.swift
   Bitset.swift
   Bool.swift
@@ -208,6 +206,9 @@ set(SWIFTLIB_SOURCES
   CollectionDifference.swift
   CollectionOfOne.swift
   Diffing.swift
+  Differentiable.swift
+  # SWIFT_ENABLE_TENSORFLOW
+  DifferentiationSupport.swift
   Mirror.swift
   PlaygroundDisplay.swift
   CommandLine.swift

stdlib/public/core/Differentiable.swift

@@ -0,0 +1,66 @@
+//===--- Differentiable.swift ---------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the Differentiable protocol, used by the experimental
+// differentiable programming project. Please see forum discussion for more
+// information:
+// https://forums.swift.org/t/differentiable-programming-mega-proposal/28547
+//
+//===----------------------------------------------------------------------===//
+
+/// A type that mathematically represents a differentiable manifold whose
+/// tangent spaces are finite-dimensional.
+public protocol _Differentiable {
+  /// A type representing a differentiable value's derivatives.
+  ///
+  /// Mathematically, this is equivalent to the tangent bundle of the
+  /// differentiable manifold represented by the differentiable type.
+  associatedtype TangentVector: _Differentiable & AdditiveArithmetic
+    where TangentVector.TangentVector == TangentVector
+
+  /// Moves `self` along the given direction. In Riemannian geometry, this is
+  /// equivalent to exponential map, which moves `self` on the geodesic surface
+  /// along the given tangent vector.
+  mutating func move(along direction: TangentVector)
+
+  // SWIFT_ENABLE_TENSORFLOW
+  /// A tangent vector such that `move(along: zeroTangentVector)` will not
+  /// modify `self`.
+  /// - Note: `zeroTangentVector` can be `TangentVector.zero` in most cases,
+  ///   but types whose tangent vectors depend on instance properties of `self`
+  ///   need to provide a different implementation. For example, the tangent
+  ///   vector of an `Array` depends on the array's `count`.
+  @available(*, deprecated, message: """
+      `zeroTangentVector` derivation has not been implemented; do not use \
+      this property
+      """)
+  var zeroTangentVector: TangentVector { get }
+}
+
+public extension _Differentiable where TangentVector == Self {
+  mutating func move(along direction: TangentVector) {
+    self += direction
+  }
+}
+
+public extension _Differentiable {
+  // This is a temporary solution that allows us to add `zeroTangentVector`
+  // without implementing derived conformances. This property is marked
+  // unavailable because it will produce incorrect results when tangent vectors
+  // depend on instance properties of `self`.
+  // FIXME: Implement derived conformance and remove this default
+  // implementation.
+  var zeroTangentVector: TangentVector { .zero }
+}
+
+// SWIFT_ENABLE_TENSORFLOW
+public typealias Differentiable = _Differentiable

stdlib/public/core/AutoDiff.swift → stdlib/public/core/DifferentiationSupport.swift

@@ -1,8 +1,8 @@
-//===--- AutoDiff.swift ---------------------------------------*- swift -*-===//
+//===--- DifferentiationSupport.swift -------------------------*- swift -*-===//
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -12,7 +12,8 @@
 //
 // SWIFT_ENABLE_TENSORFLOW
 //
-// This file defines support for automatic differentiation.
+// This file defines support for differentiable programming and deep learning
+// APIs.
 //
 //===----------------------------------------------------------------------===//
 
@@ -101,8 +102,9 @@ public extension VectorProtocol {
   }
 }
 
-/* Note: These default-implemented operators will slow down type-checking
-   performance and break existing code.
+/*
+// Note: These default-implemented operators will slow down type-checking
+// performance and break existing code.
 
 public extension VectorProtocol {
   static func + (lhs: Self, rhs: VectorSpaceScalar) -> Self {
@@ -149,50 +151,6 @@ public extension VectorProtocol where VectorSpaceScalar : SignedNumeric {
 }
 */
 
-/// A type that mathematically represents a differentiable manifold whose
-/// tangent spaces are finite-dimensional.
-public protocol Differentiable {
-  /// A type representing a differentiable value’s derivatives.
-  ///
-  /// Mathematically, this is equivalent to the tangent bundle of the
-  /// differentiable manifold represented by the differentiable type.
-  associatedtype TangentVector: Differentiable & AdditiveArithmetic
-    where TangentVector.TangentVector == TangentVector
-
-  /// Moves `self` along the given direction. In Riemannian geometry, this is
-  /// equivalent to exponential map, which moves `self` on the geodesic surface
-  /// along the given tangent vector.
-  mutating func move(along direction: TangentVector)
-
-  /// A tangent vector such that `move(along: zeroTangentVector)` will not
-  /// modify `self`.
-  /// - Note: `zeroTangentVector` can be `TangentVector.zero` in most cases,
-  ///   but types whose tangent vectors depend on instance properties of `self`
-  ///   need to provide a different implementation. For example, the tangent
-  ///   vector of an `Array` depends on the array’s `count`.
-  @available(*, deprecated, message: """
-      `zeroTangentVector` derivation has not been implemented; do not use \
-      this property
-      """)
-  var zeroTangentVector: TangentVector { get }
-}
-
-public extension Differentiable {
-  // This is a temporary solution that allows us to add `zeroTangentVector`
-  // without implementing derived conformances. This property is marked
-  // unavailable because it will produce incorrect results when tangent vectors
-  // depend on instance properties of `self`.
-  // FIXME: Implement derived conformance and remove this default
-  // implementation.
-  var zeroTangentVector: TangentVector { .zero }
-}
-
-public extension Differentiable where TangentVector == Self {
-  mutating func move(along direction: TangentVector) {
-    self += direction
-  }
-}
-
 /// A type that is differentiable in the Euclidean space.
 /// The type may represent a vector space, or consist of a vector space and some
 /// other non-differentiable component.
@@ -1077,8 +1035,9 @@ public extension Array where Element: Differentiable {
 }
 
 //===----------------------------------------------------------------------===//
-// JVP Diagnostics
+// JVP diagnostics
 //===----------------------------------------------------------------------===//
+
 @_silgen_name("_printJVPErrorAndExit")
 public func _printJVPErrorAndExit() -> Never {
     fatalError("""

stdlib/public/core/GroupInfo.json

@@ -171,9 +171,6 @@
       "SIMDVector.swift",
       "SIMDVectorTypes.swift"]}
   ],
-  "AutoDiff": [
-    "AutoDiff.swift",
-  ],
   "Optional": [
     "Optional.swift"
   ],
@@ -231,5 +228,9 @@
   ],
   "Result": [
     "Result.swift"
+  ],
+  "DifferentiableProgramming": [
+    "Differentiable.swift",
+    "DifferentiationSupport.swift"
   ]
 }

test/AutoDiff/derived_differentiable.swift

@@ -44,7 +44,7 @@ struct TestNoDerivative : EuclideanDifferentiable {
 // CHECK-AST:         var w: Float
 // CHECK-AST:         @noDerivative internal var technicallyDifferentiable: Float
 // CHECK-AST:         internal init(w: Float, technicallyDifferentiable: Float)
-// CHECK-AST:         internal struct TangentVector : Differentiable, AdditiveArithmetic, ElementaryFunctions, VectorProtocol
+// CHECK-AST:         internal struct TangentVector : _Differentiable, AdditiveArithmetic, ElementaryFunctions, VectorProtocol
 // CHECK-AST:           internal typealias TangentVector = TestNoDerivative.TangentVector
 // CHECK-AST:         internal var differentiableVectorView: TestNoDerivative.TangentVector { get }
 
@@ -57,7 +57,7 @@ struct TestPointwiseMultiplicative : Differentiable {
 // CHECK-AST:         var w: PointwiseMultiplicativeDummy
 // CHECK-AST:         @noDerivative internal var technicallyDifferentiable: PointwiseMultiplicativeDummy
 // CHECK-AST:         internal init(w: PointwiseMultiplicativeDummy, technicallyDifferentiable: PointwiseMultiplicativeDummy)
-// CHECK-AST:         internal struct TangentVector : Differentiable, AdditiveArithmetic, PointwiseMultiplicative
+// CHECK-AST:         internal struct TangentVector : _Differentiable, AdditiveArithmetic, PointwiseMultiplicative
 // CHECK-AST:           internal typealias TangentVector = TestPointwiseMultiplicative.TangentVector
 
 
@@ -70,14 +70,14 @@ struct TestKeyPathIterable : Differentiable, KeyPathIterable {
 // CHECK-AST:         var w: Float
 // CHECK-AST:         @noDerivative internal var technicallyDifferentiable: Float
 // CHECK-AST:         internal init(w: Float, technicallyDifferentiable: Float)
-// CHECK-AST:         internal struct TangentVector : Differentiable, AdditiveArithmetic, ElementaryFunctions, VectorProtocol, KeyPathIterable
+// CHECK-AST:         internal struct TangentVector : _Differentiable, AdditiveArithmetic, ElementaryFunctions, VectorProtocol, KeyPathIterable
 // CHECK-AST:           internal typealias TangentVector = TestKeyPathIterable.TangentVector
 
 struct GenericTanMember<T : Differentiable> : Differentiable, AdditiveArithmetic {
   var x: T.TangentVector
 }
 
-// CHECK-AST-LABEL: internal struct GenericTanMember<T> : Differentiable, AdditiveArithmetic where T : Differentiable
+// CHECK-AST-LABEL: internal struct GenericTanMember<T> : Differentiable, AdditiveArithmetic where T : _Differentiable
 // CHECK-AST:   internal var x: T.TangentVector
 // CHECK-AST:   internal init(x: T.TangentVector)
 // CHECK-AST:   internal typealias TangentVector = GenericTanMember<T>
@@ -92,7 +92,7 @@ public struct ConditionallyDifferentiable<T> {
 extension ConditionallyDifferentiable : Differentiable where T : Differentiable {}
 
 // CHECK-AST-LABEL: public struct ConditionallyDifferentiable<T> {
-// CHECK-AST:         @differentiable(wrt: self where T : Differentiable)
+// CHECK-AST:         @differentiable(wrt: self where T : _Differentiable)
 // CHECK-AST:         public var x: T
 // CHECK-AST:         internal init(x: T)
 // CHECK-AST:       }
@@ -121,7 +121,7 @@ final class AdditiveArithmeticClass<T : AdditiveArithmetic & Differentiable> : A
   }
 }
 
-// CHECK-AST-LABEL: final internal class AdditiveArithmeticClass<T> : AdditiveArithmetic, Differentiable where T : AdditiveArithmetic, T : Differentiable {
+// CHECK-AST-LABEL: final internal class AdditiveArithmeticClass<T> : AdditiveArithmetic, Differentiable where T : AdditiveArithmetic, T : _Differentiable {
 // CHECK-AST:         final internal var x: T, y: T
-// CHECK-AST:         internal struct TangentVector : Differentiable, AdditiveArithmetic
+// CHECK-AST:         internal struct TangentVector : _Differentiable, AdditiveArithmetic
 // CHECK-AST:       }

test/AutoDiff/differentiable_attr_silgen.swift

@@ -30,7 +30,7 @@ public func foo_indir_ret<T: Differentiable>(_ x: Float, _ y: T) -> T {
   return y
 }
 
-// CHECK-SIL-LABEL: sil [differentiable source 0 wrt 0, 1 vjp @AD__foo_indir_ret__vjp_src_0_wrt_0_1] [ossa] @foo_indir_ret : $@convention(thin) <T where T : Differentiable> (Float, @in_guaranteed T) -> @out T {
+// CHECK-SIL-LABEL: sil [differentiable source 0 wrt 0, 1 vjp @AD__foo_indir_ret__vjp_src_0_wrt_0_1] [ossa] @foo_indir_ret : $@convention(thin) <T where T : _Differentiable> (Float, @in_guaranteed T) -> @out T {
 // CHECK-SIL: bb0(%0 : $*T, %1 : $Float, %2 : $*T):
 
 @_silgen_name("dfoo_indir_ret")
@@ -101,7 +101,7 @@ struct DiffComputedProp : Differentiable & AdditiveArithmetic {
 // Check that `@differentiable` attribute is transferred from computed property
 // storage declaration to getter accessor.
 
-// CHECK-AST: struct DiffComputedProp : AdditiveArithmetic & Differentiable {
+// CHECK-AST: struct DiffComputedProp : _Differentiable & AdditiveArithmetic {
 // CHECK-AST-NEXT:   var computedProp: Float { get }
 // CHECK-AST: }
 

test/AutoDiff/differentiable_attr_type_checking.swift

@@ -765,7 +765,7 @@ struct TF_521<T: FloatingPoint> {
     self.imaginary = imaginary
   }
 }
-// expected-error @+2 {{type 'TF_521<T>' does not conform to protocol 'Differentiable'}}
+// expected-error @+2 {{type 'TF_521<T>' does not conform to protocol '_Differentiable'}}
 // expected-note @+1 {{do you want to add protocol stubs}}
 extension TF_521: Differentiable where T: Differentiable {
   // expected-note @+1 {{possibly intended match 'TF_521<T>.TangentVector' does not conform to 'AdditiveArithmetic'}}

test/AutoDiff/differentiable_func_debuginfo.swift

@@ -23,7 +23,7 @@
 // Conclusion: mangling coverage is important.
 
 // Minimal dummy compiler-known `Differentiable` protocol.
-public protocol Differentiable {
+public protocol _Differentiable {
   associatedtype TangentVector
 }
 

test/AutoDiff/differentiable_func_type_type_checking.swift

@@ -92,7 +92,7 @@ extension Vector: Differentiable where T: Differentiable {}
 func inferredConformancesGeneric<T, U>(_: @differentiable (Vector<T>) -> Vector<U>) {}
 
 func nondiffVectorFunc(x: Vector<Int>) -> Vector<Int> {}
-// expected-error @+1 {{global function 'inferredConformancesGeneric' requires that 'Int' conform to 'Differentiable}}
+// expected-error @+1 {{global function 'inferredConformancesGeneric' requires that 'Int' conform to '_Differentiable}}
 inferredConformancesGeneric(nondiffVectorFunc)
 
 func diffVectorFunc(x: Vector<Float>) -> Vector<Float> {}

test/AutoDiff/differentiable_function_silgen.swift

@@ -84,5 +84,5 @@ func appliesReabstraction(_ f: @escaping @differentiable (Float) -> Float) {
 // CHECK-SILGEN:   [[REABS_VJP:%.*]] = function_ref @$sS4fIegyd_Iegydo_S4fIegnr_Iegnro_TR : $@convention(thin) (@in_guaranteed Float, @guaranteed @callee_guaranteed (Float) -> (Float, @owned @callee_guaranteed (Float) -> Float)) -> (@out Float, @owned @callee_guaranteed (@in_guaranteed Float) -> @out Float)
 // CHECK-SILGEN:   [[NEW_VJP:%.*]] = partial_apply [callee_guaranteed] [[REABS_VJP]]([[VJP_COPY]]) : $@convention(thin) (@in_guaranteed Float, @guaranteed @callee_guaranteed (Float) -> (Float, @owned @callee_guaranteed (Float) -> Float)) -> (@out Float, @owned @callee_guaranteed (@in_guaranteed Float) -> @out Float)
 // CHECK-SILGEN:   [[NEW_DIFF_FUNC:%.*]] = differentiable_function [wrt 0] [order 1] [[NEW_ORIG]] : $@callee_guaranteed (@in_guaranteed Float) -> @out Float with {[[NEW_JVP]] : $@callee_guaranteed (@in_guaranteed Float) -> (@out Float, @owned @callee_guaranteed (@in_guaranteed Float) -> @out Float), [[NEW_VJP]] : $@callee_guaranteed (@in_guaranteed Float) -> (@out Float, @owned @callee_guaranteed (@in_guaranteed Float) -> @out Float)}
-// CHECK-SILGEN:   [[DIFF_API:%.*]] = function_ref @${{.*}}pullback{{.*}}at{{.*}} : $@convention(thin) <τ_0_0, τ_0_1 where τ_0_0 : Differentiable, τ_0_1 : Differentiable> (@in_guaranteed τ_0_0, @guaranteed @differentiable @callee_guaranteed (@in_guaranteed τ_0_0) -> @out τ_0_1) -> @owned @callee_guaranteed (@in_guaranteed τ_0_1.TangentVector) -> @out τ_0_0.TangentVector
-// CHECK-SILGEN:   apply [[DIFF_API]]<Float, Float>({{.*}}, [[NEW_DIFF_FUNC]]) : $@convention(thin) <τ_0_0, τ_0_1 where τ_0_0 : Differentiable, τ_0_1 : Differentiable> (@in_guaranteed τ_0_0, @guaranteed @differentiable @callee_guaranteed (@in_guaranteed τ_0_0) -> @out τ_0_1) -> @owned @callee_guaranteed (@in_guaranteed τ_0_1.TangentVector) -> @out τ_0_0.TangentVector
+// CHECK-SILGEN:   [[DIFF_API:%.*]] = function_ref @${{.*}}pullback{{.*}}at{{.*}} : $@convention(thin) <τ_0_0, τ_0_1 where τ_0_0 : _Differentiable, τ_0_1 : _Differentiable> (@in_guaranteed τ_0_0, @guaranteed @differentiable @callee_guaranteed (@in_guaranteed τ_0_0) -> @out τ_0_1) -> @owned @callee_guaranteed (@in_guaranteed τ_0_1.TangentVector) -> @out τ_0_0.TangentVector
+// CHECK-SILGEN:   apply [[DIFF_API]]<Float, Float>({{.*}}, [[NEW_DIFF_FUNC]]) : $@convention(thin) <τ_0_0, τ_0_1 where τ_0_0 : _Differentiable, τ_0_1 : _Differentiable> (@in_guaranteed τ_0_0, @guaranteed @differentiable @callee_guaranteed (@in_guaranteed τ_0_0) -> @out τ_0_1) -> @owned @callee_guaranteed (@in_guaranteed τ_0_1.TangentVector) -> @out τ_0_0.TangentVector