IRGen: Fix IR linkage computation for inlined function references from clang modules imported @_weakLinked.

Part of rdar://98521248

Author: tshortli

lib/IRGen/GenDecl.cpp

@@ -3282,8 +3282,8 @@ llvm::Function *IRGenModule::getAddrOfSILFunction(
         //
         // FIXME: We should be able to set the linkage unconditionally here but
         //        some fixes are needed for Cxx interop.
-        if (auto *DC = f->getDeclContext())
-          if (getSwiftModule()->isImportedAsWeakLinked(DC->getParentModule()))
+        if (auto *parentModule = f->getParentModule())
+          if (getSwiftModule()->isImportedAsWeakLinked(parentModule))
             fn->setLinkage(link.getLinkage());
       }
 

test/IRGen/weaklinked_import_inlining_clang.swift

@@ -0,0 +1,56 @@
+// RUN: %empty-directory(%t)
+// RUN: %build-irgen-test-overlays
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/Inputs -I %t) -emit-module -emit-module-path %t/Intermediate.swiftmodule -parse-as-library %t/Intermediate.swift -enable-library-evolution
+//
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/Inputs -I %t) -primary-file %t/Client.swift -emit-ir | %FileCheck %s
+
+// REQUIRES: objc_interop
+
+//--- Intermediate.swift
+
+import Foundation
+
+public func hasDefaultArgument(_ n: NSNotification = NSNotification()) { }
+
+@_alwaysEmitIntoClient
+public func aeicFuncUsingWeakVar() {
+  _ = weak_variable
+}
+
+@_alwaysEmitIntoClient
+public func aeicFuncUsingStrongVar() {
+  _ = strong_variable
+}
+
+@_alwaysEmitIntoClient
+public func aeicFuncCallingAlwaysAvailableFunc() {
+  always_available_function()
+}
+
+
+//--- Client.swift
+
+import Intermediate
+@_weakLinked import Foundation
+
+// Symbols from `Foundation` should have weak linkage even when the references
+// to them are inlined from `Intermediate`, which imported `Foundation` without
+// `@_weakLinked`.
+
+func testDefaultArguments() {
+  // CHECK-DAG: @"OBJC_CLASS_$_NSNotification" = extern_weak global %objc_class
+  hasDefaultArgument()
+}
+
+func testAlwaysEmitIntoClient() {
+  // CHECK-DAG: @weak_variable = extern_weak global
+  aeicFuncUsingWeakVar()
+  
+  // CHECK-DAG: @strong_variable = extern_weak global
+  aeicFuncUsingStrongVar()
+  
+  // CHECK-DAG: declare extern_weak void @always_available_function()
+  aeicFuncCallingAlwaysAvailableFunc()
+}