[Runtime] Use the Swift calling convention for swift_getAssociatedTypeWitness.

Runtime functions need to use the Swift calling convention for any function
returning MetadataResponse, so that we get the two values returned in separate
registers.

Fixes rdar://problem/45042971 and rdar://problem/45851050.

Author: DougGregor

include/swift/ABI/Metadata.h

@@ -167,8 +167,9 @@ using Metadata = TargetMetadata<InProcess>;
 /// The result of requesting type metadata.  Generally the return value of
 /// a function.
 ///
-/// For performance, functions returning this type should use SWIFT_CC so
-/// that the components are returned as separate values.
+/// For performance and ABI matching across Swift/C++, functions returning
+/// this type must use SWIFT_CC so that the components are returned as separate
+/// values.
 struct MetadataResponse {
   /// The requested metadata.
   const Metadata *Value;

include/swift/Runtime/Metadata.h

@@ -418,7 +418,7 @@ swift_instantiateWitnessTable(ProtocolConformanceDescriptor *conformance,
 /// \param assocType Associated type descriptor.
 ///
 /// \returns metadata for the associated type witness.
-SWIFT_RUNTIME_EXPORT
+SWIFT_RUNTIME_EXPORT SWIFT_CC(swift)
 MetadataResponse swift_getAssociatedTypeWitness(
                                           MetadataRequest request,
                                           WitnessTable *wtable,

include/swift/Runtime/RuntimeFunctions.def

@@ -651,7 +651,7 @@ FUNCTION(InstantiateWitnessTable, swift_instantiateWitnessTable, C_CC,
 //                                            const Metadata *conformingType,
 //                                            ProtocolRequirement *reqBase,
 //                                            ProtocolRequirement *assocType);
-FUNCTION(GetAssociatedTypeWitness, swift_getAssociatedTypeWitness, C_CC,
+FUNCTION(GetAssociatedTypeWitness, swift_getAssociatedTypeWitness, SwiftCC,
          RETURNS(TypeMetadataResponseTy),
          ARGS(SizeTy,
               WitnessTablePtrTy,

test/IRGen/associated_types.swift

@@ -75,7 +75,7 @@ func testFastRuncible<T: Runcible, U: FastRuncible>(_ t: T, u: U)
 //   1. Get the type metadata for U.RuncerType.Runcee.
 //     1a. Get the type metadata for U.RuncerType.
 //         Note that we actually look things up in T, which is going to prove unfortunate.
-// CHECK: [[T2:%.*]] = call %swift.metadata_response @swift_getAssociatedTypeWitness([[INT]] 0, i8** %T.Runcible, %swift.type* %T, %swift.protocol_requirement* getelementptr{{.*}}i32 12), i32 -1), %swift.protocol_requirement* getelementptr inbounds (<{{.*}}>, <{{.*}}>* @"$s16associated_types8RuncibleMp", i32 0, i32 14)) [[NOUNWIND_READNONE:#.*]]
+// CHECK: [[T2:%.*]] = call swiftcc %swift.metadata_response @swift_getAssociatedTypeWitness([[INT]] 0, i8** %T.Runcible, %swift.type* %T, %swift.protocol_requirement* getelementptr{{.*}}i32 12), i32 -1), %swift.protocol_requirement* getelementptr inbounds (<{{.*}}>, <{{.*}}>* @"$s16associated_types8RuncibleMp", i32 0, i32 14)) [[NOUNWIND_READNONE:#.*]]
 // CHECK-NEXT: %T.RuncerType = extractvalue %swift.metadata_response [[T2]], 0
 // CHECK-NEXT: store %swift.type*
 //   2. Get the witness table for U.RuncerType.Runcee : Speedy
@@ -85,7 +85,7 @@ func testFastRuncible<T: Runcible, U: FastRuncible>(_ t: T, u: U)
 // CHECK-NEXT: [[T2:%.*]] = bitcast i8* [[T1]] to i8** (%swift.type*, %swift.type*, i8**)*
 // CHECK-NEXT: %T.RuncerType.FastRuncer = call swiftcc i8** [[T2]](%swift.type* %T.RuncerType, %swift.type* %U, i8** %U.FastRuncible)
 //     1c. Get the type metadata for U.RuncerType.Runcee.
-// CHECK-NEXT: [[T2:%.*]] = call %swift.metadata_response @swift_getAssociatedTypeWitness([[INT]] 0, i8** %T.RuncerType.FastRuncer, %swift.type* %T.RuncerType, {{.*}}, %swift.protocol_requirement* getelementptr inbounds (<{{.*}}>, <{{.*}}>* @"$s16associated_types10FastRuncerMp", i32 0, i32 10))
+// CHECK-NEXT: [[T2:%.*]] = call swiftcc %swift.metadata_response @swift_getAssociatedTypeWitness([[INT]] 0, i8** %T.RuncerType.FastRuncer, %swift.type* %T.RuncerType, {{.*}}, %swift.protocol_requirement* getelementptr inbounds (<{{.*}}>, <{{.*}}>* @"$s16associated_types10FastRuncerMp", i32 0, i32 10))
 // CHECK-NEXT: %T.RuncerType.Runcee = extractvalue %swift.metadata_response [[T2]], 0
 // CHECK-NEXT: store %swift.type*
 //     2b. Get the witness table for U.RuncerType.Runcee : Speedy.

test/IRGen/generic_structs.sil

@@ -256,7 +256,7 @@ struct GenericLayoutWithAssocType<T: ParentHasAssociatedType> {
 // CHECK: [[T0_GEP:%.*]] = getelementptr inbounds i8*, i8** %T.ParentHasAssociatedType, i32 1
 // CHECK: [[T0:%.*]] = load i8*, i8** [[T0_GEP]]
 // CHECK: [[T1:%.*]] = bitcast i8* [[T0]] to i8**
-// CHECK: [[T4:%.*]] = call %swift.metadata_response @swift_getAssociatedTypeWitness(i64 0, i8** %T.HasAssociatedType, %swift.type* %T, %swift.protocol_requirement* @"$s15generic_structs17HasAssociatedTypeTL", %swift.protocol_requirement* @"$s5Assoc15generic_structs17HasAssociatedTypePTl")
+// CHECK: [[T4:%.*]] = call swiftcc %swift.metadata_response @swift_getAssociatedTypeWitness(i64 0, i8** %T.HasAssociatedType, %swift.type* %T, %swift.protocol_requirement* @"$s15generic_structs17HasAssociatedTypeTL", %swift.protocol_requirement* @"$s5Assoc15generic_structs17HasAssociatedTypePTl")
 
 // CHECK: %T.Assoc = extractvalue %swift.metadata_response [[T4]], 0
 
@@ -265,5 +265,5 @@ struct GenericLayoutWithAssocType<T: ParentHasAssociatedType> {
 // CHECK:   [[T2:%.*]] = bitcast i8* [[T1]] to i8** (%swift.type*, %swift.type*, i8**)*
 // CHECK:   %T.Assoc.HasAssociatedType = call swiftcc i8** [[T2]](%swift.type* %T.Assoc, %swift.type* %T, i8** %T.ParentHasAssociatedType)
 
-// CHECK:   [[T2:%.*]] = call %swift.metadata_response @swift_getAssociatedTypeWitness(i64 0, i8** %T.Assoc.HasAssociatedType, %swift.type* %T.Assoc, %swift.protocol_requirement* @"$s15generic_structs17HasAssociatedTypeTL", %swift.protocol_requirement* @"$s5Assoc15generic_structs17HasAssociatedTypePTl")
+// CHECK:   [[T2:%.*]] = call swiftcc %swift.metadata_response @swift_getAssociatedTypeWitness(i64 0, i8** %T.Assoc.HasAssociatedType, %swift.type* %T.Assoc, %swift.protocol_requirement* @"$s15generic_structs17HasAssociatedTypeTL", %swift.protocol_requirement* @"$s5Assoc15generic_structs17HasAssociatedTypePTl")
 // CHECK:   %T.Assoc.Assoc = extractvalue %swift.metadata_response [[T2]], 0

test/IRGen/protocol_resilience_descriptors.swift

@@ -82,7 +82,7 @@ where Element: ProtocolWithRequirements, Element.T == Y {
 
 // CHECK-USAGE: define{{( dllexport)?}}{{( protected)?}} swiftcc %swift.type* @"$s31protocol_resilience_descriptors17assocTypeMetadatay1TQzmxm010resilient_A024ProtocolWithRequirementsRzlF"(%swift.type*, %swift.type* [[PWD:%.*]], i8** [[WTABLE:%.*]])
 public func assocTypeMetadata<PWR: ProtocolWithRequirements>(_: PWR.Type) -> PWR.T.Type {
-  // CHECK-USAGE: call %swift.metadata_response @swift_getAssociatedTypeWitness([[INT]] 0, i8** %PWR.ProtocolWithRequirements, %swift.type* %PWR, %swift.protocol_requirement* @"$s18resilient_protocol24ProtocolWithRequirementsTL", %swift.protocol_requirement* @"$s1T18resilient_protocol24ProtocolWithRequirementsPTl")
+  // CHECK-USAGE: call swiftcc %swift.metadata_response @swift_getAssociatedTypeWitness([[INT]] 0, i8** %PWR.ProtocolWithRequirements, %swift.type* %PWR, %swift.protocol_requirement* @"$s18resilient_protocol24ProtocolWithRequirementsTL", %swift.protocol_requirement* @"$s1T18resilient_protocol24ProtocolWithRequirementsPTl")
   return PWR.T.self
 }