IRGen: Weak-link references to swift_getExtendedExistentialTypeMetadata()

Fixes rdar://117530421.

Author: slavapestov

include/swift/Runtime/RuntimeFunctions.def

@@ -1177,7 +1177,8 @@ FUNCTION(GetExistentialMetadata,
 // swift_getExtendedExistentialTypeShape(
 //             const NonUniqueExtendedExistentialTypeShape *nonUnique);
 FUNCTION(GetExtendedExistentialTypeShape,
-         swift_getExtendedExistentialTypeShape, C_CC, AlwaysAvailable,
+         swift_getExtendedExistentialTypeShape, C_CC,
+         ParameterizedExistentialAvailability,
          RETURNS(TypeMetadataPtrTy),
          ARGS(Int8PtrTy, Int8PtrPtrTy),
          ATTRS(NoUnwind, ArgMemOnly, WillReturn),
@@ -1187,7 +1188,8 @@ FUNCTION(GetExtendedExistentialTypeShape,
 //             const NonUniqueExtendedExistentialTypeShape *shape,
 //             const void * const *generalizationArgs);
 FUNCTION(GetExtendedExistentialTypeMetadata,
-         swift_getExtendedExistentialTypeMetadata, C_CC, AlwaysAvailable,
+         swift_getExtendedExistentialTypeMetadata, C_CC,
+         ParameterizedExistentialAvailability,
          RETURNS(TypeMetadataPtrTy),
          ARGS(Int8PtrTy, Int8PtrPtrTy),
          ATTRS(NoUnwind, ArgMemOnly, WillReturn),
@@ -1197,7 +1199,8 @@ FUNCTION(GetExtendedExistentialTypeMetadata,
 //             const ExtendedExistentialTypeShape *shape,
 //             const void * const *generalizationArgs);
 FUNCTION(GetExtendedExistentialTypeMetadataUnique,
-         swift_getExtendedExistentialTypeMetadata_unique, C_CC, AlwaysAvailable,
+         swift_getExtendedExistentialTypeMetadata_unique, C_CC,
+         ParameterizedExistentialAvailability,
          RETURNS(TypeMetadataPtrTy),
          ARGS(Int8PtrTy, Int8PtrPtrTy),
          ATTRS(NoUnwind, ArgMemOnly, WillReturn),

lib/IRGen/IRGenModule.cpp

@@ -924,6 +924,14 @@ namespace RuntimeConstants {
     return RuntimeAvailability::ConditionallyAvailable;
   }
 
+  RuntimeAvailability ParameterizedExistentialAvailability(ASTContext &Context) {
+    auto featureAvailability = Context.getParameterizedExistentialRuntimeAvailability();
+    if (!isDeploymentAvailabilityContainedIn(Context, featureAvailability)) {
+      return RuntimeAvailability::ConditionallyAvailable;
+    }
+    return RuntimeAvailability::AlwaysAvailable;
+  }
+
 } // namespace RuntimeConstants
 
 // We don't use enough attributes to justify generalizing the

test/IRGen/extended_existential_metadata_weak.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -emit-ir %s -target %target-swift-abi-5.5-triple | %FileCheck %s
+// REQUIRES: VENDOR=apple
+
+public protocol P<A> {
+  associatedtype A
+}
+
+public func f<T>(_: T.Type) {}
+
+@available(SwiftStdlib 5.7, *)
+public func g<T>(_: T.Type) { f((any P<T>).self) }
+
+// CHECK-LABEL: declare extern_weak {{.*}} @swift_getExtendedExistentialTypeMetadata(