public func takes_p1(_: T.Type) {} public protocol P1 { associatedtype AT1 func normal() func generic(_: T) } public protocol P2 { associatedtype AT2: P3 } public protocol P3 { associatedtype AT3 } public struct Nothing {} public struct IsP2: P2 { public typealias AT2 = IsP3 } public struct IsP3: P3 { public typealias AT3 = Nothing } public struct IsAlsoP2: P2 { public typealias AT2 = IsBoth } public struct IsBoth: P2, P3 { public typealias AT2 = HoldsP3 public typealias AT3 = Nothing } public struct HoldsP3: P3 { public typealias AT3 = IsP3 } public struct Double {} extension Double: P1 where B.AT2: P2, C: P3, B.AT2.AT2.AT3: P3 { public typealias AT1 = C public func normal() {} public func generic(_: T) {} } // witness method for Double.normal // CHECK-LABEL: define linkonce_odr hidden swiftcc void @"$s34conditional_conformance_with_assoc6DoubleVyxq_GAA2P1A2A2P3R_AA2P23AT2RpzAafH_AhaGP3AT3RPzrlAaEP6normalyyFTW"(%T34conditional_conformance_with_assoc6DoubleV* noalias nocapture swiftself %0, %swift.type* %Self, i8** %SelfWitnessTable) // CHECK-NEXT: entry: // CHECK-NEXT: [[C_P3_PTR:%.*]] = getelementptr inbounds i8*, i8** %SelfWitnessTable, i32 -1 // CHECK-NEXT: [[C_P3:%.*]] = load i8*, i8** [[C_P3_PTR]], align 8 // CHECK-NEXT: %"\CF\84_0_1.P3" = bitcast i8* [[C_P3]] to i8** // CHECK-NEXT: [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8*, i8** %SelfWitnessTable, i32 -2 // CHECK-NEXT: [[B_AT2_P2:%.*]] = load i8*, i8** [[B_AT2_P2_PTR]], align 8 // CHECK-NEXT: %"\CF\84_0_0.AT2.P2" = bitcast i8* [[B_AT2_P2]] to i8** // CHECK-NEXT: [[B_AT2_AT2_AT3_P3_PTR:%.*]] = getelementptr inbounds i8*, i8** %SelfWitnessTable, i32 -3 // CHECK-NEXT: [[B_AT2_AT2_AT3_P3:%.*]] = load i8*, i8** [[B_AT2_AT2_AT3_P3_PTR]], align 8 // CHECK-NEXT: %"\CF\84_0_0.AT2.AT2.AT3.P3" = bitcast i8* [[B_AT2_AT2_AT3_P3]] to i8** // CHECK-NEXT: [[SELF_AS_TYPE_ARRAY:%.*]] = bitcast %swift.type* %Self to %swift.type** // CHECK-NEXT: [[B_PTR:%.*]] = getelementptr inbounds %swift.type*, %swift.type** [[SELF_AS_TYPE_ARRAY]], i64 2 // CHECK-NEXT: [[B:%.*]] = load %swift.type*, %swift.type** [[B_PTR]], align 8 // CHECK-NEXT: [[SELF_AS_TYPE_ARRAY_2:%.*]] = bitcast %swift.type* %Self to %swift.type** // CHECK-NEXT: [[C_PTR:%.*]] = getelementptr inbounds %swift.type*, %swift.type** [[SELF_AS_TYPE_ARRAY_2]], i64 3 // CHECK-NEXT: [[C:%.*]] = load %swift.type*, %swift.type** [[C_PTR]], align 8 // CHECK-NEXT: [[SELF_AS_WT_ARRAY:%.*]] = bitcast %swift.type* %Self to i8*** // CHECK-NEXT: [[B_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[SELF_AS_WT_ARRAY]], i64 4 // CHECK-NEXT: %"\CF\84_0_0.P2" = load i8**, i8*** [[B_P2_PTR]], align 8 // CHECK-NEXT: call swiftcc void @"$s34conditional_conformance_with_assoc6DoubleVA2A2P3R_AA2P23AT2RpzAadF_AfaEP3AT3RPzrlE6normalyyF"(%swift.type* %"\CF\84_0_0", %swift.type* %"\CF\84_0_1", i8** %"\CF\84_0_0.P2", i8** %"\CF\84_0_1.P3", i8** %"\CF\84_0_0.AT2.P2", i8** %"\CF\84_0_0.AT2.AT2.AT3.P3") // CHECK-NEXT: ret void // CHECK-NEXT: } // witness method for Double.generic // CHECK-LABEL: define linkonce_odr hidden swiftcc void @"$s34conditional_conformance_with_assoc6DoubleVyxq_GAA2P1A2A2P3R_AA2P23AT2RpzAafH_AhaGP3AT3RPzrlAaEP7genericyyqd__AaFRd__lFTW"(%swift.opaque* noalias nocapture %0, %swift.type* %"\CF\84_1_0", i8** %"\CF\84_1_0.P3", %T34conditional_conformance_with_assoc6DoubleV* noalias nocapture swiftself %1, %swift.type* %Self, i8** %SelfWitnessTable) // CHECK-NEXT: entry: // CHECK-NEXT: [[C_P3_PTR:%.*]] = getelementptr inbounds i8*, i8** %SelfWitnessTable, i32 -1 // CHECK-NEXT: [[C_P3:%.*]] = load i8*, i8** [[C_P3_PTR]], align 8 // CHECK-NEXT: %"\CF\84_0_1.P3" = bitcast i8* [[C_P3]] to i8** // CHECK-NEXT: [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8*, i8** %SelfWitnessTable, i32 -2 // CHECK-NEXT: [[B_AT2_P2:%.*]] = load i8*, i8** [[B_AT2_P2_PTR]], align 8 // CHECK-NEXT: %"\CF\84_0_0.AT2.P2" = bitcast i8* [[B_AT2_P2]] to i8** // CHECK-NEXT: [[B_AT2_AT2_AT3_P3_PTR:%.*]] = getelementptr inbounds i8*, i8** %SelfWitnessTable, i32 -3 // CHECK-NEXT: [[B_AT2_AT2_AT3_P3:%.*]] = load i8*, i8** [[B_AT2_AT2_AT3_P3_PTR]], align 8 // CHECK-NEXT: %"\CF\84_0_0.AT2.AT2.AT3.P3" = bitcast i8* [[B_AT2_AT2_AT3_P3]] to i8** // CHECK-NEXT: [[SELF_AS_TYPE_ARRAY:%.*]] = bitcast %swift.type* %Self to %swift.type** // CHECK-NEXT: [[B_PTR:%.*]] = getelementptr inbounds %swift.type*, %swift.type** [[SELF_AS_TYPE_ARRAY]], i64 2 // CHECK-NEXT: [[B:%.*]] = load %swift.type*, %swift.type** [[B_PTR]], align 8 // CHECK-NEXT: [[SELF_AS_TYPE_ARRAY_2:%.*]] = bitcast %swift.type* %Self to %swift.type** // CHECK-NEXT: [[C_PTR:%.*]] = getelementptr inbounds %swift.type*, %swift.type** [[SELF_AS_TYPE_ARRAY_2]], i64 3 // CHECK-NEXT: [[C:%.*]] = load %swift.type*, %swift.type** [[C_PTR]], align 8 // CHECK-NEXT: [[SELF_AS_WT_ARRAY:%.*]] = bitcast %swift.type* %Self to i8*** // CHECK-NEXT: [[B_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[SELF_AS_WT_ARRAY]], i64 4 // CHECK-NEXT: %"\CF\84_0_0.P2" = load i8**, i8*** [[B_P2_PTR]], align 8 // CHECK-NEXT: call swiftcc void @"$s34conditional_conformance_with_assoc6DoubleVA2A2P3R_AA2P23AT2RpzAadF_AfaEP3AT3RPzrlE7genericyyqd__AaDRd__lF"(%swift.opaque* noalias nocapture %0, %swift.type* %"\CF\84_0_0", %swift.type* %"\CF\84_0_1", %swift.type* %"\CF\84_1_0", i8** %"\CF\84_0_0.P2", i8** %"\CF\84_0_1.P3", i8** %"\CF\84_1_0.P3", i8** %"\CF\84_0_0.AT2.P2", i8** %"\CF\84_0_0.AT2.AT2.AT3.P3") // CHECK-NEXT: ret void // CHECK-NEXT: } public func generic_generic(_: T.Type, _: U.Type) where T.AT2: P2, U: P3, T.AT2.AT2.AT3: P3 { takes_p1(Double.self) } // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc void @"$s34conditional_conformance_with_assoc08generic_E0yyxm_q_mtAA2P2RzAA2P3R_AaC3AT2RpzAadE_AeaCP3AT3RPzr0_lF"(%swift.type* %0, %swift.type* %1, %swift.type* %T, %swift.type* %U, i8** %T.P2, i8** %U.P3, i8** %T.AT2.P2, i8** %T.AT2.AT2.AT3.P3) // CHECK-NEXT: entry: // CHECK: %conditional.requirement.buffer = alloca [3 x i8**], align 8 // CHECK: [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s34conditional_conformance_with_assoc6DoubleVMa"(i64 0, %swift.type* %T, %swift.type* %U, i8** %T.P2) // CHECK-NEXT: [[Double_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0 // CHECK-NEXT: [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [3 x i8**], [3 x i8**]* %conditional.requirement.buffer, i32 0, i32 0 // CHECK-NEXT: [[C_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0 // CHECK-NEXT: store i8** %U.P3, i8*** [[C_P3_PTR]], align 8 // CHECK-NEXT: [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 1 // CHECK-NEXT: store i8** %T.AT2.P2, i8*** [[B_AT2_P2_PTR]], align 8 // CHECK-NEXT: [[B_AT2_AT2_AT3_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 2 // CHECK-NEXT: store i8** %T.AT2.AT2.AT3.P3, i8*** [[B_AT2_AT2_AT3_P3_PTR]], align 8 // CHECK-NEXT: [[Double_P1:%.*]] = call i8** @swift_getWitnessTable // CHECK-NEXT: call swiftcc void @"$s34conditional_conformance_with_assoc8takes_p1yyxmAA2P1RzlF"(%swift.type* [[Double_TYPE]], %swift.type* [[Double_TYPE]], i8** [[Double_P1]]) // CHECK-NEXT: ret void // CHECK-NEXT: } public func generic_concrete(_: T.Type) where T.AT2: P2, T.AT2.AT2.AT3: P3 { takes_p1(Double.self) } // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc void @"$s34conditional_conformance_with_assoc16generic_concreteyyxmAA2P2RzAaC3AT2RpzAA2P3AD_AdaCP3AT3RPzlF"(%swift.type* %0, %swift.type* %T, i8** %T.P2, i8** %T.AT2.P2, i8** %T.AT2.AT2.AT3.P3) // CHECK-NEXT: entry: // CHECK: %conditional.requirement.buffer = alloca [3 x i8**], align 8 // CHECK: [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s34conditional_conformance_with_assoc6DoubleVMa"( // CHECK-SAME: i64 0, // CHECK-SAME: %swift.type* // CHECK-SAME: %T, // CHECK-SAME: %swift.type* bitcast ( // CHECK-SAME: i64* getelementptr inbounds ( // CHECK-SAME: <{ // CHECK-SAME: i8**, // CHECK-SAME: i64, // CHECK-SAME: <{ {{[^}]*}} }>* // CHECK-SAME: }>, // CHECK-SAME: <{ {{.*}} }>* @"$s34conditional_conformance_with_assoc4IsP3VMf", // CHECK-SAME: i32 0, // CHECK-SAME: i32 1 // CHECK-SAME: ) to %swift.type* // CHECK-SAME: ), // CHECK-SAME: i8** %T.P2 // CHECK-SAME: ) // CHECK-NEXT: [[Double_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0 // CHECK-NEXT: [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [3 x i8**], [3 x i8**]* %conditional.requirement.buffer, i32 0, i32 0 // CHECK-NEXT: [[C_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0 // CHECK-NEXT: store i8** getelementptr inbounds ([2 x i8*], [2 x i8*]* @"$s34conditional_conformance_with_assoc4IsP3VAA0F0AAWP", i32 0, i32 0), i8*** [[C_P3_PTR]], align 8 // CHECK-NEXT: [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 1 // CHECK-NEXT: store i8** %T.AT2.P2, i8*** [[B_AT2_P2_PTR]], align 8 // CHECK-NEXT: [[B_AT2_AT2_AT3_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 2 // CHECK-NEXT: store i8** %T.AT2.AT2.AT3.P3, i8*** [[B_AT2_AT2_AT3_P3_PTR]], align 8 // CHECK-NEXT: [[Double_P1:%.*]] = call i8** @swift_getWitnessTable // CHECK-NEXT: call swiftcc void @"$s34conditional_conformance_with_assoc8takes_p1yyxmAA2P1RzlF"(%swift.type* [[Double_TYPE]], %swift.type* [[Double_TYPE]], i8** [[Double_P1]]) // CHECK-NEXT: ret void // CHECK-NEXT: } public func concrete_generic(_: U.Type) where U: P3 { takes_p1(Double.self) } // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc void @"$s34conditional_conformance_with_assoc16concrete_genericyyxmAA2P3RzlF"(%swift.type* %0, %swift.type* %U, i8** %U.P3) // CHECK-NEXT: entry: // CHECK: %conditional.requirement.buffer = alloca [3 x i8**], align 8 // CHECK: [[T0:%.*]] = call swiftcc %swift.metadata_response @"$s34conditional_conformance_with_assoc6DoubleVMa"(i64 0, %swift.type* bitcast (i64* getelementptr inbounds (<{ {{.*}} }>, <{ {{.*}} }>* @"$s34conditional_conformance_with_assoc8IsAlsoP2VMf", i32 0, i32 1) to %swift.type*), %swift.type* %U, i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @"$s34conditional_conformance_with_assoc8IsAlsoP2VAA0G0AAWP", i32 0, i32 0)) // CHECK-NEXT: [[Double_TYPE:%.*]] = extractvalue %swift.metadata_response [[T0]], 0 // CHECK-NEXT: [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [3 x i8**], [3 x i8**]* %conditional.requirement.buffer, i32 0, i32 0 // CHECK-NEXT: [[C_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0 // CHECK-NEXT: store i8** %U.P3, i8*** [[C_P3_PTR]], align 8 // CHECK-NEXT: [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 1 // CHECK-NEXT: store i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @"$s34conditional_conformance_with_assoc6IsBothVAA2P2AAWP", i32 0, i32 0), i8*** [[B_AT2_P2_PTR]], align 8 // CHECK-NEXT: [[B_AT2_AT2_AT3_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 2 // CHECK-NEXT: store i8** getelementptr inbounds ([2 x i8*], [2 x i8*]* @"$s34conditional_conformance_with_assoc4IsP3VAA0F0AAWP", i32 0, i32 0), i8*** [[B_AT2_AT2_AT3_P3_PTR]], align 8 // CHECK-NEXT: [[Double_P1:%.*]] = call i8** @swift_getWitnessTable // CHECK-NEXT: call swiftcc void @"$s34conditional_conformance_with_assoc8takes_p1yyxmAA2P1RzlF"(%swift.type* [[Double_TYPE]], %swift.type* [[Double_TYPE]], i8** [[Double_P1]]) // CHECK-NEXT: ret void // CHECK-NEXT:} public func concrete_concrete() { takes_p1(Double.self) } // CHECK-LABEL: define{{( dllexport)?}}{{( protected)?}} swiftcc void @"$s34conditional_conformance_with_assoc09concrete_E0yyF"() // CHECK-NEXT: entry: // CHECK-NEXT: [[Z:%.*]] = call i8** @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGACyxq_GAA2P1A2A0I0R_AA0H03AT2RpzAakM_AmaLP3AT3RPzrlWl"() // CHECK-NEXT: call swiftcc void @"$s34conditional_conformance_with_assoc8takes_p1yyxmAA2P1RzlF"( // CHECK-SAME: %swift.type* getelementptr inbounds ( // CHECK-SAME: %swift.full_type, // CHECK-SAME: %swift.full_type* bitcast ( // CHECK-SAME: <{ // CHECK-SAME: i8**, // CHECK-SAME: [[INT]], // CHECK-SAME: %swift.type_descriptor*, // CHECK-SAME: %swift.type*, // CHECK-SAME: %swift.type*, // CHECK-SAME: i8**, // CHECK-SAME: i64 // CHECK-SAME: }>* @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGMf" // CHECK-SAME: to %swift.full_type* // CHECK-SAME: ), // CHECK-SAME: i32 0, // CHECK-SAME: i32 1 // CHECK-SAME: ), // CHECK-SAME: %swift.type* getelementptr inbounds ( // CHECK-SAME: %swift.full_type, // CHECK-SAME: %swift.full_type* bitcast ( // CHECK-SAME: <{ // CHECK-SAME: i8**, // CHECK-SAME: [[INT]], // CHECK-SAME: %swift.type_descriptor*, // CHECK-SAME: %swift.type*, // CHECK-SAME: %swift.type*, // CHECK-SAME: i8**, // CHECK-SAME: i64 // CHECK-SAME: }>* @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGMf" // CHECK-SAME: to %swift.full_type* // CHECK-SAME: ), // CHECK-SAME: i32 0, // CHECK-SAME: i32 1 // CHECK-SAME: ) // CHECK-SAME: ) // CHECK-NEXT: ret void // CHECK-NEXT: } // Lazy witness table accessor for the concrete Double : P1. // CHECK-LABEL: define linkonce_odr hidden i8** @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGACyxq_GAA2P1A2A0I0R_AA0H03AT2RpzAakM_AmaLP3AT3RPzrlWl"() // CHECK-NEXT: entry: // CHECK-NEXT: %conditional.requirement.buffer = alloca [3 x i8**], align 8 // CHECK-NEXT: [[CACHE:%.*]] = load i8**, i8*** @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGACyxq_GAA2P1A2A0I0R_AA0H03AT2RpzAakM_AmaLP3AT3RPzrlWL", align 8 // CHECK-NEXT: [[IS_NULL:%.*]] = icmp eq i8** [[CACHE]], null // CHECK-NEXT: br i1 [[IS_NULL]], label %cacheIsNull, label %cont // CHECK: cacheIsNull: // CHECK-NEXT: [[CONDITIONAL_REQUIREMENTS:%.*]] = getelementptr inbounds [3 x i8**], [3 x i8**]* %conditional.requirement.buffer, i32 0, i32 0 // CHECK-NEXT: [[C_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 0 // CHECK-NEXT: store i8** getelementptr inbounds ([2 x i8*], [2 x i8*]* @"$s34conditional_conformance_with_assoc4IsP3VAA0F0AAWP", i32 0, i32 0), i8*** [[C_P3_PTR]], align 8 // CHECK-NEXT: [[B_AT2_P2_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 1 // CHECK-NEXT: store i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @"$s34conditional_conformance_with_assoc6IsBothVAA2P2AAWP", i32 0, i32 0), i8*** [[B_AT2_P2_PTR]], align 8 // CHECK-NEXT: [[B_AT2_AT2_AT3_P3_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[CONDITIONAL_REQUIREMENTS]], i32 2 // CHECK-NEXT: store i8** getelementptr inbounds ([2 x i8*], [2 x i8*]* @"$s34conditional_conformance_with_assoc4IsP3VAA0F0AAWP", i32 0, i32 0), i8*** [[B_AT2_AT2_AT3_P3_PTR]], align 8 // CHECK-NEXT: [[Double_P1:%.*]] = call i8** @swift_getWitnessTable( // CHECK-SAME: %swift.protocol_conformance_descriptor* bitcast ( // CHECK-SAME: { i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i16, i16, i32, i32 }* // CHECK-SAME: @"$s34conditional_conformance_with_assoc6DoubleVyxq_GAA2P1A2A2P3R_AA2P23AT2RpzAafH_AhaGP3AT3RPzrlMc" // CHECK-SAME: to %swift.protocol_conformance_descriptor* // CHECK-SAME: ), // CHECK-SAME: %swift.type* getelementptr inbounds ( // CHECK-SAME: %swift.full_type, // CHECK-SAME: %swift.full_type* bitcast ( // CHECK-SAME: <{ // CHECK-SAME: i8**, // CHECK-SAME: [[INT]], // CHECK-SAME: %swift.type_descriptor*, // CHECK-SAME: %swift.type*, // CHECK-SAME: %swift.type*, // CHECK-SAME: i8**, // CHECK-SAME: i64 // CHECK-SAME: }>* @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGMf" // CHECK-SAME: to %swift.full_type* // CHECK-SAME: ), // CHECK-SAME: i32 0, // CHECK-SAME: i32 1 // CHECK-SAME: ), // CHECK-SAME: i8*** [[CONDITIONAL_REQUIREMENTS]] // CHECK-SAME: ) // CHECK-NEXT: store atomic i8** [[Double_P1]], i8*** @"$s34conditional_conformance_with_assoc6DoubleVyAA8IsAlsoP2VAA0F2P3VGACyxq_GAA2P1A2A0I0R_AA0H03AT2RpzAakM_AmaLP3AT3RPzrlWL" release, align 8 // CHECK-NEXT: br label %cont // CHECK: cont: // CHECK-NEXT: [[T0:%.*]] = phi i8** [ [[CACHE]], %entry ], [ [[Double_P1]], %cacheIsNull ] // CHECK-NEXT: ret i8** [[T0]] // CHECK-NEXT: } protocol Base { } protocol Sub : Base { associatedtype S : Base } struct X { } extension X: Base where T: Base { } extension X: Sub where T: Sub, T.S == T { typealias S = X }