Merge pull request #24259 from bob-wilson/rdar50110036-51-0424

References to _swift_FORCE_LOAD* symbols should be weak

Author: bob-wilson

include/swift/IRGen/Linking.h

@@ -1075,6 +1075,7 @@ struct IRLinkage {
   static const IRLinkage Internal;
 
   static const IRLinkage ExternalImport;
+  static const IRLinkage ExternalWeakImport;
   static const IRLinkage ExternalExport;
 };
 

lib/IRGen/IRGenModule.cpp

@@ -981,8 +981,12 @@ void IRGenModule::addLinkLibrary(const LinkLibrary &linkLib) {
     encodeForceLoadSymbolName(buf, linkLib.getName());
     auto ForceImportThunk =
         Module.getOrInsertFunction(buf, llvm::FunctionType::get(VoidTy, false));
-    ApplyIRLinkage(IRLinkage::ExternalImport)
-        .to(cast<llvm::GlobalValue>(ForceImportThunk));
+
+    const IRLinkage IRL =
+        llvm::Triple(Module.getTargetTriple()).isOSBinFormatCOFF()
+            ? IRLinkage::ExternalImport
+            : IRLinkage::ExternalWeakImport;
+    ApplyIRLinkage(IRL).to(cast<llvm::GlobalValue>(ForceImportThunk));
 
     buf += "_$";
     appendEncodedName(buf, IRGen.Opts.ModuleName);

lib/IRGen/Linking.cpp

@@ -57,6 +57,12 @@ const IRLinkage IRLinkage::ExternalImport = {
   llvm::GlobalValue::DLLImportStorageClass,
 };
 
+const IRLinkage IRLinkage::ExternalWeakImport = {
+  llvm::GlobalValue::ExternalWeakLinkage,
+  llvm::GlobalValue::DefaultVisibility,
+  llvm::GlobalValue::DLLImportStorageClass,
+};
+
 const IRLinkage IRLinkage::ExternalExport = {
   llvm::GlobalValue::ExternalLinkage,
   llvm::GlobalValue::DefaultVisibility,

test/Serialization/autolinking.swift

@@ -13,7 +13,7 @@
 // RUN: %target-swift-frontend -emit-module -parse-stdlib -o %t -module-name someModule -module-link-name module %S/../Inputs/empty.swift -autolink-force-load
 // RUN: %target-swift-frontend -emit-ir -lmagic %s -I %t > %t/force-load.txt
 // RUN: %FileCheck %s < %t/force-load.txt
-// RUN: %FileCheck -check-prefix=FORCE-LOAD-CLIENT %s < %t/force-load.txt
+// RUN: %FileCheck -check-prefix FORCE-LOAD-CLIENT -check-prefix FORCE-LOAD-CLIENT-%target-object-format %s < %t/force-load.txt
 
 // RUN: %target-swift-frontend -emit-ir -parse-stdlib -module-name someModule -module-link-name module %S/../Inputs/empty.swift | %FileCheck --check-prefix=NO-FORCE-LOAD %s
 // RUN: %target-swift-frontend -emit-ir -parse-stdlib -module-name someModule -module-link-name module %S/../Inputs/empty.swift -autolink-force-load | %FileCheck --check-prefix=FORCE-LOAD %s
@@ -49,5 +49,6 @@ import someModule
 // FORCE-LOAD-CLIENT: @llvm.used = appending global [{{[0-9]+}} x i8*] [
 // FORCE-LOAD-CLIENT: i8* bitcast (void ()** @"_swift_FORCE_LOAD_$_module_$_autolinking" to i8*)
 // FORCE-LOAD-CLIENT: ], section "llvm.metadata"
-// FORCE-LOAD-CLIENT: declare {{(dllimport )?}}void @"_swift_FORCE_LOAD_$_module"()
+// FORCE-LOAD-CLIENT-MACHO: declare extern_weak {{(dllimport )?}}void @"_swift_FORCE_LOAD_$_module"()
+// FORCE-LOAD-CLIENT-COFF: declare extern {{(dllimport )?}}void @"_swift_FORCE_LOAD_$_module"()