[embedded] Emit weak_odr instead of linkonce_odr symbols under -Xfrontend -mergeable-symbols

lib/IRGen/GenDecl.cpp

@@ -2273,7 +2273,7 @@ getIRLinkage(StringRef name, const UniversalLinkageInfo &info,
     auto linkage = llvm::GlobalValue::ExternalLinkage;
 
     if (info.MergeableSymbols)
-      linkage = llvm::GlobalValue::LinkOnceODRLinkage;
+      linkage = llvm::GlobalValue::WeakODRLinkage;
 
     return {linkage, PublicDefinitionVisibility,
             info.Internalize ? llvm::GlobalValue::DefaultStorageClass
@@ -2291,7 +2291,7 @@ getIRLinkage(StringRef name, const UniversalLinkageInfo &info,
 
   case SILLinkage::Hidden:
     if (info.MergeableSymbols)
-      return RESULT(LinkOnceODR, Hidden, Default);
+      return RESULT(WeakODR, Hidden, Default);
 
     return RESULT(External, Hidden, Default);
 

test/embedded/linkage-custom-entry-point.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-frontend %s -module-name Application -parse-as-library -entry-point-function-name Application_main -mergeable-symbols    -enable-experimental-feature Embedded -emit-ir | %FileCheck %s
+// RUN: %target-swift-frontend %s -module-name Application -parse-as-library -entry-point-function-name Application_main -mergeable-symbols -O -enable-experimental-feature Embedded -emit-ir | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: swift_feature_Embedded
+
+@main
+struct Main {
+  static func main() {
+    print("hello")
+  }
+}
+
+// CHECK: @Application_main

test/embedded/linkage-mergeable-dead-strip.swift

@@ -0,0 +1,26 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -enable-experimental-feature Embedded -enable-experimental-feature SymbolLinkageMarkers -module-name main -mergeable-symbols -O %s -emit-ir | %FileCheck %s --check-prefix=CHECK-IR
+// RUN: %target-swift-frontend -enable-experimental-feature Embedded -enable-experimental-feature SymbolLinkageMarkers -module-name main -mergeable-symbols -O %s -c -o %t/a.o
+// RUN: %target-clang %t/a.o -o %t/a.out -dead_strip
+// RUN: %llvm-nm --defined-only --format=just-symbols --demangle %t/a.out | sort | %FileCheck %s --check-prefix=CHECK-NM
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: executable_test
+// REQUIRES: swift_feature_Embedded
+// REQUIRES: swift_feature_SymbolLinkageMarkers
+
+public func a_this_is_unused() { }
+
+@_used
+public func b_this_is_unused_but_explicitly_retained() { }
+
+// CHECK-IR: define weak_odr {{.*}}@"$e4main16a_this_is_unusedyyF"()
+// CHECK-IR: define weak_odr {{.*}}@"$e4main40b_this_is_unused_but_explicitly_retainedyyF"()
+
+// CHECK-NM-NOT: $e4main14this_is_unusedyyF
+// CHECK-NM: $e4main40b_this_is_unused_but_explicitly_retainedyyF
+
+print("Hello")
+// CHECK: Hello

test/embedded/linkage-linkonce-odr.swift → test/embedded/linkage-mergeable.swift

@@ -8,7 +8,6 @@
 
 // REQUIRES: swift_in_compiler
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=linux-gnu
 // REQUIRES: swift_feature_Embedded
 
 // BEGIN MyModule.swift

test/embedded/linkage-mergeable2.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: %{python} %utils/split_file.py -o %t %s
+
+// RUN: %target-swift-frontend -mergeable-symbols -O -c -emit-module -o %t/MyModule.o %t/MyModule.swift   -enable-experimental-feature Embedded -parse-as-library
+// RUN: %target-swift-frontend -mergeable-symbols -O -c              -o %t/a.o        %t/Main.swift -I %t -enable-experimental-feature Embedded
+// RUN: %target-clang %t/a.o %t/MyModule.o -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: executable_test
+// REQUIRES: swift_feature_Embedded
+
+// BEGIN MyModule.swift
+
+public func module_func() {
+  print("module_func")
+}
+
+public func module_generic_func<T: CustomStringConvertible>(t: T) {
+  print("module_generic_func: \(t)")
+}
+
+// BEGIN Main.swift
+
+import MyModule
+
+func test() {
+  module_func()
+  module_generic_func(t: 42)
+}
+
+test()
+
+// CHECK: module_func
+// CHECK: module_generic_func: 42

test/embedded/linkage-public-exports.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend %s -mergeable-symbols    -enable-experimental-feature Embedded -emit-ir | %FileCheck %s
+// RUN: %target-swift-frontend %s -mergeable-symbols -O -enable-experimental-feature Embedded -emit-ir | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: swift_feature_Embedded
+
+public func foo1() { }
+
+func foo2() { }
+
+// CHECK: foo1
+// CHECK-NOT: foo2